Investigations into the nutritional requirements of juvenile dusky kob, Argyrosomus japonicus (Pisces sciaendae), under ambient culture conditions
- Authors: Daniel, Simon James
- Date: 2004
- Subjects: Argyrosomus -- Nutrition -- Requirements , Sciaenidae -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Fishes -- Nutrition -- Requirements
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5197 , http://hdl.handle.net/10962/d1002602 , Argyrosomus -- Nutrition -- Requirements , Sciaenidae -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Fishes -- Nutrition -- Requirements
- Description: The effect of dietary protein, protein and energy ratios, fish meal replacement by Soya bean meal and feeding frequency was investigated on the growth, feed efficiency and body composition, of juvenile dusky kob, Argyrosomus japonicus. The effect of dietary protein levels was investigated by comparing isocaloric diets containing 35, 40, 45 and 55% protein. Dietary protein inclusion level significantly affected specific growth rates, feed efficiency and body composition (in terms of fat deposition) and results show that a minimum of 45% and maximum of 52.3% dietary protein is optimal. The protein and energy requirements were investigated by comparing three protein levels (35,40 and 45%) with three lipid levels (6, 9 and 12%) in a 3x3 factorial design. A diet 45% protein and 9% lipid, with a P: E ratio of29 mglkJ and DE of 15.5 kJ/g resulted in an optimal specific growth rate (1.6± 0.2), feed efficiency (FCR= 1.7±0.44; PER= 1.36) and body composition for A. japonicus. To investigate the effect of partial fish meal replacement by Soya bean meal (SBM) in the diet, 20-50% of the protein from fish meal was substituted by protein from SBM, and were compared with a control diet containing only fish meal. No significant differences in the specific growth rates, feed efficiencies and the body composition were recorded for the fish fed the control diet and for fish fed the 20 and 30% SBM treatments. Results show that up to 30% of the protein from fish meal can be replaced with protein from SBM in the diet of this species. The effect of feeding frequency and gut evacuation time was investigated by comparing four feeding frequencies. Fish were fed to satiation either once, twice, three or four times a day. Feed intake was significantly affected by feeding frequency and fish fed 2, 3 and 4 meals a day ate significantly more food (p< 0.05) than the fish fed one meal a day. No significant differences (p> 0.05) in the specific growth rates, feed efficiencies and body composition were recorded for fish fed 2, 3 and 4 times a day. Feed intake was used to calculate an optimal daily ration and feeding two meals a day resulted in an optimal daily ration of 4% BW/day. A gut evacuation time of 7.25 hours indicates that fish fed twice a day probably had sufficient time to digest their food and evacuate their guts, resulting in the same daily feed intake as fish given 3 and 4 meals a day. Results conclude that under the present experimental conditions, a minimum daily ration of 4% BW/day, fed twice a day (in the morning and evening) is required for optimal growth (SGR= 1.33± 0.1), feed efficiency (FCR= 1.96± 0.4; PER= 1.44± 0.2) and body composition in juvenile dusky kob.
- Full Text:
- Date Issued: 2004
- Authors: Daniel, Simon James
- Date: 2004
- Subjects: Argyrosomus -- Nutrition -- Requirements , Sciaenidae -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Fishes -- Nutrition -- Requirements
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5197 , http://hdl.handle.net/10962/d1002602 , Argyrosomus -- Nutrition -- Requirements , Sciaenidae -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Fishes -- Nutrition -- Requirements
- Description: The effect of dietary protein, protein and energy ratios, fish meal replacement by Soya bean meal and feeding frequency was investigated on the growth, feed efficiency and body composition, of juvenile dusky kob, Argyrosomus japonicus. The effect of dietary protein levels was investigated by comparing isocaloric diets containing 35, 40, 45 and 55% protein. Dietary protein inclusion level significantly affected specific growth rates, feed efficiency and body composition (in terms of fat deposition) and results show that a minimum of 45% and maximum of 52.3% dietary protein is optimal. The protein and energy requirements were investigated by comparing three protein levels (35,40 and 45%) with three lipid levels (6, 9 and 12%) in a 3x3 factorial design. A diet 45% protein and 9% lipid, with a P: E ratio of29 mglkJ and DE of 15.5 kJ/g resulted in an optimal specific growth rate (1.6± 0.2), feed efficiency (FCR= 1.7±0.44; PER= 1.36) and body composition for A. japonicus. To investigate the effect of partial fish meal replacement by Soya bean meal (SBM) in the diet, 20-50% of the protein from fish meal was substituted by protein from SBM, and were compared with a control diet containing only fish meal. No significant differences in the specific growth rates, feed efficiencies and the body composition were recorded for the fish fed the control diet and for fish fed the 20 and 30% SBM treatments. Results show that up to 30% of the protein from fish meal can be replaced with protein from SBM in the diet of this species. The effect of feeding frequency and gut evacuation time was investigated by comparing four feeding frequencies. Fish were fed to satiation either once, twice, three or four times a day. Feed intake was significantly affected by feeding frequency and fish fed 2, 3 and 4 meals a day ate significantly more food (p< 0.05) than the fish fed one meal a day. No significant differences (p> 0.05) in the specific growth rates, feed efficiencies and body composition were recorded for fish fed 2, 3 and 4 times a day. Feed intake was used to calculate an optimal daily ration and feeding two meals a day resulted in an optimal daily ration of 4% BW/day. A gut evacuation time of 7.25 hours indicates that fish fed twice a day probably had sufficient time to digest their food and evacuate their guts, resulting in the same daily feed intake as fish given 3 and 4 meals a day. Results conclude that under the present experimental conditions, a minimum daily ration of 4% BW/day, fed twice a day (in the morning and evening) is required for optimal growth (SGR= 1.33± 0.1), feed efficiency (FCR= 1.96± 0.4; PER= 1.44± 0.2) and body composition in juvenile dusky kob.
- Full Text:
- Date Issued: 2004
Screening of the white margined sole, Synaptura marginata (Soleidae), as a candidate for aquaculture in South Africa
- Authors: Thompson, Ernst Frederick
- Date: 2004
- Subjects: Flatfishes -- South Africa , Aquaculture -- South Africa , Soleidae -- South Africa , Soleidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5207 , http://hdl.handle.net/10962/d1004523 , Flatfishes -- South Africa , Aquaculture -- South Africa , Soleidae -- South Africa , Soleidae
- Description: The white margined sole Synaptura marginata (Soleidae) was isolated as the most likely candidate for flatfish aquaculture in South Africa. The aim of the study was to screen the sole as a candidate aquaculture species by way of a comprehensive study of its biology and life history strategy and to identify possible "bottlenecks". The study was undertaken on the assumption that the biological data would provide valuable information for developing specific technologies that might be required for the farming of this species. Specimens were collected monthly by spearing along the Eastern Cape coast of South Africa between December 2000 and March 2002. Length-at-age data required for modeling the growth of S. marginata was obtained from sectioned otoliths. A Von Bertalanffy growth model with an absolute error structure best describes the growth for this species. The model parameters were: L∞ = 429.5 mm TL, K = 0.24 and t₀ = -1 .79 years. Analysis of gut contents showed that S. marginata feed exclusively on polychaete worms, mainly of the genus Morphysa. S. marginata shows a protracted summer spawning season of six months, from October to April. This was determined by the calculation of a monthly gonadosomatic index and a macroscopic maturity scale. Histological examination of the ovaries revealed five ovarian developmental stages. Size at 50% and 100% sexual maturity for females was calculated to be 235 mm TL and 300 mm TL (ca. 1.5 - 2.5 years of age) and all males> 154 mm TL were mature. S. marginata is a batch spawner, releasing a minimum of 3 batches of eggs per year. Relative fecundity is high (34000 eggs per year I kg) and this coupled with the protracted spawning season would make it possible to obtain adequate numbers of juveniles (for farming) for approximately five to six months of the year. Comparative analysis of the biological characteristics in relation to other soles farmed elsewhere in the world suggests that S. marginata is a suitable candidate for marine fish culture in South Africa.
- Full Text:
- Date Issued: 2004
- Authors: Thompson, Ernst Frederick
- Date: 2004
- Subjects: Flatfishes -- South Africa , Aquaculture -- South Africa , Soleidae -- South Africa , Soleidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5207 , http://hdl.handle.net/10962/d1004523 , Flatfishes -- South Africa , Aquaculture -- South Africa , Soleidae -- South Africa , Soleidae
- Description: The white margined sole Synaptura marginata (Soleidae) was isolated as the most likely candidate for flatfish aquaculture in South Africa. The aim of the study was to screen the sole as a candidate aquaculture species by way of a comprehensive study of its biology and life history strategy and to identify possible "bottlenecks". The study was undertaken on the assumption that the biological data would provide valuable information for developing specific technologies that might be required for the farming of this species. Specimens were collected monthly by spearing along the Eastern Cape coast of South Africa between December 2000 and March 2002. Length-at-age data required for modeling the growth of S. marginata was obtained from sectioned otoliths. A Von Bertalanffy growth model with an absolute error structure best describes the growth for this species. The model parameters were: L∞ = 429.5 mm TL, K = 0.24 and t₀ = -1 .79 years. Analysis of gut contents showed that S. marginata feed exclusively on polychaete worms, mainly of the genus Morphysa. S. marginata shows a protracted summer spawning season of six months, from October to April. This was determined by the calculation of a monthly gonadosomatic index and a macroscopic maturity scale. Histological examination of the ovaries revealed five ovarian developmental stages. Size at 50% and 100% sexual maturity for females was calculated to be 235 mm TL and 300 mm TL (ca. 1.5 - 2.5 years of age) and all males> 154 mm TL were mature. S. marginata is a batch spawner, releasing a minimum of 3 batches of eggs per year. Relative fecundity is high (34000 eggs per year I kg) and this coupled with the protracted spawning season would make it possible to obtain adequate numbers of juveniles (for farming) for approximately five to six months of the year. Comparative analysis of the biological characteristics in relation to other soles farmed elsewhere in the world suggests that S. marginata is a suitable candidate for marine fish culture in South Africa.
- Full Text:
- Date Issued: 2004
The development of a geographic information system (GIS) as a mariculture sector planning tool in South Africa
- Authors: Shiran-Klotz, Imran
- Date: 2004
- Subjects: Geographic information systems -- South Africa , Fishery management -- Geographic information systems -- South Africa , Mariculture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5337 , http://hdl.handle.net/10962/d1005870 , Geographic information systems -- South Africa , Fishery management -- Geographic information systems -- South Africa , Mariculture -- South Africa
- Description: The South African coastline has a high potential for mariculture development, particularly in land-based systems, due to excellent water quality, good infrastructure, and relatively cheap land in certain areas. Development of mariculture however, has been slow primarily due to the absence of a national sector development plan to coordinate contribution to development by government, industry and academia. Recent mariculture development plans however, supported by government commitment to stimulate coastal development, offers new opportunity for the sector's growth. These new sector development plans require a multi-disciplinary intensive information base with a strong regional and national spatial component. Geographic Information System (GIS) is a spatial analytical tool, which is capable of handling such large coastal databases and analysing them. Nevertheless, many mariculture GIS planning applications, often developed in isolation and with limited practical use for decision makers, highlighted the need to develop GIS in relation to the mariculture sector development plan. Hence, the aim of this study was to develop and evaluate a GIS for the national and regional mariculture sector planning process in South Africa, in order to identify potentially suitable areas along the South African coastline for mariculture operations. The GIS development in this study was based on the mariculture planning approach developed by PAP/RAe (1996), which recognizes the variations of scales in mariculture planning. Three case studies, representing the diversity of the South African sector plan, were selected to develop the GIS. They included: a national suitability analysis for all land-based culture systems, a specific national analysis on abalone ranching, and a detailed regional analysis of land-based culture and abalone ranching along the Namaqualand coastline. The GIS was developed separately for each case study based on a strategy consisting of six main phases, including: identification of project requirements, developing analytical framework, selection and location of data sources, organization and manipulation of data, analysing data and verifying and evaluation of the outputs. Biophysical, coastal use, and infrastructure criteria were collected, sorted and analysed to identify development constraints. Based on a set of conditions, and Boolean logic and arithmetic operations, unsuitable areas were identified and eliminated. Main constraints for national land-based development included competition over space along KwaZuluNatal Province coastline and restricted access to the coast along the south region of the Northern Cape Province, Wild Coast along the Eastern Cape Province, and Maputaland along KwaZulu-Natal Province. Ten areas along the country coastline were therefore identified as potentially suitable for land-based mariculture. Furthermore, South African abalone ranching potential was found to be limited mostly along the Western and Northern Cape Province's coastline due to the high risk of Paralytic Shellfish Poison (PSP) occurrences, alternative resource use and activities such as commercial fishery, poaching, and conservation. Hence, a total of nine areas along the Northern Cape, Western Cape, and Eastern Cape coastlines were identified as premier areas for abalone ranching. The regional study along the Namaqualand coastline revealed potential conflict between mining activity and mariculture development due to security issues and restricted access to the coast. Land-based mariculture development was confined to the four main coastal urban areas. The highest potential for land-based mariculture was along Port Nolloth and Kleinsee coastlines, whereas marine-based (i.e. abalone ranching) potential was poor along the north part of the coast due to intense marine mining activities, restricted access to the coast, and low kelp bed density. High potential abalone ranching areas were identified south to Kleinsee, and around Port Nolloth. Potential conflict with marine mining activity was minimal since it was localised and not related to kelp bed locations. It was concluded that GIS is a relevant and compatible tool for South African mariculture sector planning. However, future development of GIS as integrated planning tool in mariculture and coastal planning, requires updated spatial data (e.g. recreational activity), and continued interaction among project planners, mariculture specialists and GIS analysts.
- Full Text:
- Date Issued: 2004
- Authors: Shiran-Klotz, Imran
- Date: 2004
- Subjects: Geographic information systems -- South Africa , Fishery management -- Geographic information systems -- South Africa , Mariculture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5337 , http://hdl.handle.net/10962/d1005870 , Geographic information systems -- South Africa , Fishery management -- Geographic information systems -- South Africa , Mariculture -- South Africa
- Description: The South African coastline has a high potential for mariculture development, particularly in land-based systems, due to excellent water quality, good infrastructure, and relatively cheap land in certain areas. Development of mariculture however, has been slow primarily due to the absence of a national sector development plan to coordinate contribution to development by government, industry and academia. Recent mariculture development plans however, supported by government commitment to stimulate coastal development, offers new opportunity for the sector's growth. These new sector development plans require a multi-disciplinary intensive information base with a strong regional and national spatial component. Geographic Information System (GIS) is a spatial analytical tool, which is capable of handling such large coastal databases and analysing them. Nevertheless, many mariculture GIS planning applications, often developed in isolation and with limited practical use for decision makers, highlighted the need to develop GIS in relation to the mariculture sector development plan. Hence, the aim of this study was to develop and evaluate a GIS for the national and regional mariculture sector planning process in South Africa, in order to identify potentially suitable areas along the South African coastline for mariculture operations. The GIS development in this study was based on the mariculture planning approach developed by PAP/RAe (1996), which recognizes the variations of scales in mariculture planning. Three case studies, representing the diversity of the South African sector plan, were selected to develop the GIS. They included: a national suitability analysis for all land-based culture systems, a specific national analysis on abalone ranching, and a detailed regional analysis of land-based culture and abalone ranching along the Namaqualand coastline. The GIS was developed separately for each case study based on a strategy consisting of six main phases, including: identification of project requirements, developing analytical framework, selection and location of data sources, organization and manipulation of data, analysing data and verifying and evaluation of the outputs. Biophysical, coastal use, and infrastructure criteria were collected, sorted and analysed to identify development constraints. Based on a set of conditions, and Boolean logic and arithmetic operations, unsuitable areas were identified and eliminated. Main constraints for national land-based development included competition over space along KwaZuluNatal Province coastline and restricted access to the coast along the south region of the Northern Cape Province, Wild Coast along the Eastern Cape Province, and Maputaland along KwaZulu-Natal Province. Ten areas along the country coastline were therefore identified as potentially suitable for land-based mariculture. Furthermore, South African abalone ranching potential was found to be limited mostly along the Western and Northern Cape Province's coastline due to the high risk of Paralytic Shellfish Poison (PSP) occurrences, alternative resource use and activities such as commercial fishery, poaching, and conservation. Hence, a total of nine areas along the Northern Cape, Western Cape, and Eastern Cape coastlines were identified as premier areas for abalone ranching. The regional study along the Namaqualand coastline revealed potential conflict between mining activity and mariculture development due to security issues and restricted access to the coast. Land-based mariculture development was confined to the four main coastal urban areas. The highest potential for land-based mariculture was along Port Nolloth and Kleinsee coastlines, whereas marine-based (i.e. abalone ranching) potential was poor along the north part of the coast due to intense marine mining activities, restricted access to the coast, and low kelp bed density. High potential abalone ranching areas were identified south to Kleinsee, and around Port Nolloth. Potential conflict with marine mining activity was minimal since it was localised and not related to kelp bed locations. It was concluded that GIS is a relevant and compatible tool for South African mariculture sector planning. However, future development of GIS as integrated planning tool in mariculture and coastal planning, requires updated spatial data (e.g. recreational activity), and continued interaction among project planners, mariculture specialists and GIS analysts.
- Full Text:
- Date Issued: 2004
The effect of diet type and feeding rate on growth, morphological development and behaviour of larval and juvenile goldfish Carassius auratus (L.)
- Authors: Paulet, Timothy Guy
- Date: 2004
- Subjects: Goldfish -- Growth , Goldfish -- Nutrition , Goldfish -- Development , Goldfish -- Larvae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5271 , http://hdl.handle.net/10962/d1005115 , Goldfish -- Growth , Goldfish -- Nutrition , Goldfish -- Development , Goldfish -- Larvae
- Description: Intensive grow-out of goldfish, Carassius auratus (L.), larvae and juveniles in closed recirculating systems requires the control of environmental conditions and feeding. This study investigated the effect of different diets, environmental condition and feeding level on growth, development and survival of goldfish larvae and juveniles. Prey preference for Artemia nauplii or decapsulated Artemia cysts as well as agonistic behaviour was recorded. The micrometer device used to measure mouth-gape was shown to produce accurate measurements which could be used to estimate the maximal particle size that can be ingested by goldfish larvae of a particular age. Goldfish completed metamorphosis earlier with an increased feeding level of Artemia cysts and by making the cysts more accessible to the fish using up-welling water movement. Morphometric plasticity in goldfish larvae was exhibited within two weeks of growth and it may be possible to induce changes in morphology by manipulating diet and rearing environment. Fish that fed on moving prey items had a significantly larger mouth-gape than those that browsed cysts from the tank bottom or dry food items. The development of mouth-gape was not affected by the feeding level of cysts. Condition factor increased with an increase in the number of cysts fed per fish per day. Goldfish larvae and juveniles grew faster and had a higher survival when fed on decapsulated Artemia cysts than on instar I Artemia nauplii or a mixed live/dry diet of Artemia nauplii and dry food. Feeding at least 155 cysts per fish per day, in tanks with upwelling water movement, gave the best growth and survival and the smallest size variation. In addition, cysts remained available to the fish for longer periods, and were easier to prepare and feed. Goldfish larvae preferred decapsulated Artemia cysts to nauplii and rejected fewer prey items as they grew older. The frequency of agonistic behaviour increased as fish grew but no cannibalism was recorded for cyst-fed fish. This study showed that decapsulated Artemia cysts are a good alternative to Artemia nauplii as a diet for larval goldfish. Good growth and high survival was achieved for cyst-fed goldfish larvae and juveniles at 23 ± 1.5°C and at an initial stocking density of 12 fish per litre. This research also contributes to an understanding of feeding behaviour and attempts to minimise under- or over-feeding of Artemia cysts in order to reduce grow-out costs due to the high value of the feed type.
- Full Text:
- Date Issued: 2004
- Authors: Paulet, Timothy Guy
- Date: 2004
- Subjects: Goldfish -- Growth , Goldfish -- Nutrition , Goldfish -- Development , Goldfish -- Larvae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5271 , http://hdl.handle.net/10962/d1005115 , Goldfish -- Growth , Goldfish -- Nutrition , Goldfish -- Development , Goldfish -- Larvae
- Description: Intensive grow-out of goldfish, Carassius auratus (L.), larvae and juveniles in closed recirculating systems requires the control of environmental conditions and feeding. This study investigated the effect of different diets, environmental condition and feeding level on growth, development and survival of goldfish larvae and juveniles. Prey preference for Artemia nauplii or decapsulated Artemia cysts as well as agonistic behaviour was recorded. The micrometer device used to measure mouth-gape was shown to produce accurate measurements which could be used to estimate the maximal particle size that can be ingested by goldfish larvae of a particular age. Goldfish completed metamorphosis earlier with an increased feeding level of Artemia cysts and by making the cysts more accessible to the fish using up-welling water movement. Morphometric plasticity in goldfish larvae was exhibited within two weeks of growth and it may be possible to induce changes in morphology by manipulating diet and rearing environment. Fish that fed on moving prey items had a significantly larger mouth-gape than those that browsed cysts from the tank bottom or dry food items. The development of mouth-gape was not affected by the feeding level of cysts. Condition factor increased with an increase in the number of cysts fed per fish per day. Goldfish larvae and juveniles grew faster and had a higher survival when fed on decapsulated Artemia cysts than on instar I Artemia nauplii or a mixed live/dry diet of Artemia nauplii and dry food. Feeding at least 155 cysts per fish per day, in tanks with upwelling water movement, gave the best growth and survival and the smallest size variation. In addition, cysts remained available to the fish for longer periods, and were easier to prepare and feed. Goldfish larvae preferred decapsulated Artemia cysts to nauplii and rejected fewer prey items as they grew older. The frequency of agonistic behaviour increased as fish grew but no cannibalism was recorded for cyst-fed fish. This study showed that decapsulated Artemia cysts are a good alternative to Artemia nauplii as a diet for larval goldfish. Good growth and high survival was achieved for cyst-fed goldfish larvae and juveniles at 23 ± 1.5°C and at an initial stocking density of 12 fish per litre. This research also contributes to an understanding of feeding behaviour and attempts to minimise under- or over-feeding of Artemia cysts in order to reduce grow-out costs due to the high value of the feed type.
- Full Text:
- Date Issued: 2004
The reproductive biology and artificial breeding of ningu Labeo victorianus (Pisces: Cyprinidae)
- Authors: Rutaisire, Justus
- Date: 2004
- Subjects: Fishes -- Victoria, Lake , Cyprinidae -- Reproduction , Labeo -- Reproduction , Labeo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5317 , http://hdl.handle.net/10962/d1005162
- Description: Lake Victoria, the largest tropical lake, has faced an unprecedented assault on its ecosystem through a variety of anthropomorphic causes that include the introduction of Nile perch Lates niloticus and over-fishing. As a result there have been species extinctions and declining fish population trends. This thesis explores options for reversing these declining population trends and the restoration of collapsed fisheries based on indigenous non-cichlid species. A candidate species was chosen - the cyprinid fish Labeo victorianus. This thesis studied various aspects of L. victorianus' reproductive biology in two geographically distant populations. These included general reproductive patterns in relation to proximate environmental conditions, gonadal development and recrudescence, sex development, characterisation of genetic and morphological diversity, and induced spawning. Fish from both populations were found to be potamodrometic, and highly fecund, iteroparous spawners. L. victorianus was also shown to be an undifferentiated gonochorist, where all individuals pass through an intersexual juvenile stage prior to differentiation, and maturation to either sex. Sexual maturity was attained at a significantly larger size within the Kagera River than that of Sio River fish – possibly as a response to genotypic and/or phenotypic differences. Spawning seemed to be synchronised with rainfall in Kagera River - a pattern that was not strictly adhered to with the Sio River. Thorough microscopic investigation of recrudescence patterns indicated there was uninterrupted spawning in fish from the Kagera River followed by Type I oocyte atresia. In contrast, there was a 90% spawning failure, as characterised by Type II oocyte atresia, within the Sio River population. Aspects of spermatogenesis and sperm ultrastructure using light- and ultramicrotomic methods are described. Although the populations had varying reproductive biology parameters and were morphologically distinct, they remained undifferentiated at the mitochondrial level. Both populations were characterised by low nucleotide diversity – a feature attributed to a bottleneck event. The option of captive breeding was explored by conducting induced spawning experiments. Success was only achieved with a decapeptide Gonadotropic Releasing Hormone ([D-Arg⁶, Pro⁹-NEt])-sGnRH) in combination with a water-soluble dopamine receptor antagonist metoclopramide. This thesis stresses the importance of a research-oriented approach in the conservation of Lake Victoria's indigenous fish resources. It was concluded that information needed for the development of management policies can be generated within a reasonably short time period, of approximately three years, with modest levels of funding support.
- Full Text:
- Date Issued: 2004
- Authors: Rutaisire, Justus
- Date: 2004
- Subjects: Fishes -- Victoria, Lake , Cyprinidae -- Reproduction , Labeo -- Reproduction , Labeo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5317 , http://hdl.handle.net/10962/d1005162
- Description: Lake Victoria, the largest tropical lake, has faced an unprecedented assault on its ecosystem through a variety of anthropomorphic causes that include the introduction of Nile perch Lates niloticus and over-fishing. As a result there have been species extinctions and declining fish population trends. This thesis explores options for reversing these declining population trends and the restoration of collapsed fisheries based on indigenous non-cichlid species. A candidate species was chosen - the cyprinid fish Labeo victorianus. This thesis studied various aspects of L. victorianus' reproductive biology in two geographically distant populations. These included general reproductive patterns in relation to proximate environmental conditions, gonadal development and recrudescence, sex development, characterisation of genetic and morphological diversity, and induced spawning. Fish from both populations were found to be potamodrometic, and highly fecund, iteroparous spawners. L. victorianus was also shown to be an undifferentiated gonochorist, where all individuals pass through an intersexual juvenile stage prior to differentiation, and maturation to either sex. Sexual maturity was attained at a significantly larger size within the Kagera River than that of Sio River fish – possibly as a response to genotypic and/or phenotypic differences. Spawning seemed to be synchronised with rainfall in Kagera River - a pattern that was not strictly adhered to with the Sio River. Thorough microscopic investigation of recrudescence patterns indicated there was uninterrupted spawning in fish from the Kagera River followed by Type I oocyte atresia. In contrast, there was a 90% spawning failure, as characterised by Type II oocyte atresia, within the Sio River population. Aspects of spermatogenesis and sperm ultrastructure using light- and ultramicrotomic methods are described. Although the populations had varying reproductive biology parameters and were morphologically distinct, they remained undifferentiated at the mitochondrial level. Both populations were characterised by low nucleotide diversity – a feature attributed to a bottleneck event. The option of captive breeding was explored by conducting induced spawning experiments. Success was only achieved with a decapeptide Gonadotropic Releasing Hormone ([D-Arg⁶, Pro⁹-NEt])-sGnRH) in combination with a water-soluble dopamine receptor antagonist metoclopramide. This thesis stresses the importance of a research-oriented approach in the conservation of Lake Victoria's indigenous fish resources. It was concluded that information needed for the development of management policies can be generated within a reasonably short time period, of approximately three years, with modest levels of funding support.
- Full Text:
- Date Issued: 2004
Towards the development of species-specific fish production models for small reservoirs in Southern Africa
- Authors: Potts, Warren M
- Date: 2004
- Subjects: Freshwater fishes -- Africa, Southern Fish populations -- Africa, Southern Fisheries -- Africa, Southern Sustainable fisheries -- Africa, Southern Labeo -- Reproduction Cyprinidae -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5330 , http://hdl.handle.net/10962/d1005176
- Description: The fish populations in small southern African reservoirs are largely unexploited and there is potential for fisheries development. However, the development of sustainable fisheries requires reliable estimates of potential yield or production. Empirical models that have been developed to predict fish production only apply to large water bodies and only predict total fish production, not the production of individual species. Small reservoirs generally have few commercially important species and therefore species-specific fish production models are an alternative approach. The small reservoirs of the Eastern Cape are dominated by the moggel (Labeo umbratus). The principal objectives of this thesis were to gain an understanding of the ecology of small reservoirs and the function of moggel in these systems. This information was used to design a research approach to rapidly develop species-specific models for small reservoirs in southern Africa. The limnology of two small reservoirs was compared. During the study period the reservoirs were turbid and showed a warm, monomictic pattern of thermal stratification. Anthropogenic pressure in the reservoir catchments appeared to be the overriding factor increasing the nutrient input to the reservoirs and consequently, influencing the biomass of algae in the reservoirs. The feeding biology of moggel in Katriver and Laing reservoirs was examined. Moggel are detrivorous and successfully digested diatoms. The slower growth rate of moggel in Katriver reservoir was attributed to the poorer nutritional value of the diet as a consequence of the lower concentration of diatoms in the detrital aggregate. The reproductive characteristics of moggel were examined in four reservoirs. Moggel were able to reproduce successfully in the reservoirs. This could be attributed to their r-selected reproductive strategy, with a high fecundity and an extended spawning season and their ability to spawn in a floodplain environment. Differences in recruitment success between years were found to be a consequence of the timing and duration of seasonal rains. The number of mature females in a population and the availability of suitable spawning habitat influenced recruitment success. The life history of the moggel in five reservoirs was compared. Growth appeared to be related to food availability, while mortality was lower in the populations where food was abundant and there were less predatory species. Size and age at maturity were not affected by environmental factors, but were dependent on growth and mortality. Three contrasting methods were used to estimate moggel gillnet selectivity. The Sechin, direct fyke net method and length-structured model all yielded similar results and correction factors obtained from the selectivity study were applied to the gillnet data to estimate the fish population size and structure in each reservoir. Using information from the life history and selectivity studies, the biomass and production of five moggel populations was estimated and related to abiotic and biotic factors in the reservoirs and their catchments. Moggel biomass and production was dependent on the biomass of algae, which was dependent on morphoedaphic characteristics of the reservoirs. Small, shallow reservoirs with a reasonable amount of human habitation in their catchments would sustain the highest algal biomass and provided they had adequate spawning habitat would also have the highest moggel biomass and production. The future research requirements for small reservoir fisheries are outlined and include a three-year program to develop a species-specific production model for any of the dominant species.
- Full Text:
- Date Issued: 2004
- Authors: Potts, Warren M
- Date: 2004
- Subjects: Freshwater fishes -- Africa, Southern Fish populations -- Africa, Southern Fisheries -- Africa, Southern Sustainable fisheries -- Africa, Southern Labeo -- Reproduction Cyprinidae -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5330 , http://hdl.handle.net/10962/d1005176
- Description: The fish populations in small southern African reservoirs are largely unexploited and there is potential for fisheries development. However, the development of sustainable fisheries requires reliable estimates of potential yield or production. Empirical models that have been developed to predict fish production only apply to large water bodies and only predict total fish production, not the production of individual species. Small reservoirs generally have few commercially important species and therefore species-specific fish production models are an alternative approach. The small reservoirs of the Eastern Cape are dominated by the moggel (Labeo umbratus). The principal objectives of this thesis were to gain an understanding of the ecology of small reservoirs and the function of moggel in these systems. This information was used to design a research approach to rapidly develop species-specific models for small reservoirs in southern Africa. The limnology of two small reservoirs was compared. During the study period the reservoirs were turbid and showed a warm, monomictic pattern of thermal stratification. Anthropogenic pressure in the reservoir catchments appeared to be the overriding factor increasing the nutrient input to the reservoirs and consequently, influencing the biomass of algae in the reservoirs. The feeding biology of moggel in Katriver and Laing reservoirs was examined. Moggel are detrivorous and successfully digested diatoms. The slower growth rate of moggel in Katriver reservoir was attributed to the poorer nutritional value of the diet as a consequence of the lower concentration of diatoms in the detrital aggregate. The reproductive characteristics of moggel were examined in four reservoirs. Moggel were able to reproduce successfully in the reservoirs. This could be attributed to their r-selected reproductive strategy, with a high fecundity and an extended spawning season and their ability to spawn in a floodplain environment. Differences in recruitment success between years were found to be a consequence of the timing and duration of seasonal rains. The number of mature females in a population and the availability of suitable spawning habitat influenced recruitment success. The life history of the moggel in five reservoirs was compared. Growth appeared to be related to food availability, while mortality was lower in the populations where food was abundant and there were less predatory species. Size and age at maturity were not affected by environmental factors, but were dependent on growth and mortality. Three contrasting methods were used to estimate moggel gillnet selectivity. The Sechin, direct fyke net method and length-structured model all yielded similar results and correction factors obtained from the selectivity study were applied to the gillnet data to estimate the fish population size and structure in each reservoir. Using information from the life history and selectivity studies, the biomass and production of five moggel populations was estimated and related to abiotic and biotic factors in the reservoirs and their catchments. Moggel biomass and production was dependent on the biomass of algae, which was dependent on morphoedaphic characteristics of the reservoirs. Small, shallow reservoirs with a reasonable amount of human habitation in their catchments would sustain the highest algal biomass and provided they had adequate spawning habitat would also have the highest moggel biomass and production. The future research requirements for small reservoir fisheries are outlined and include a three-year program to develop a species-specific production model for any of the dominant species.
- Full Text:
- Date Issued: 2004
An investigation into the feeding biology and factors influencing the population dynamics of Terebrasabella heterouncinata (Polychaeta: Sabellidae), a problematic tube-dwelling polychaete in farmed abalone in South Africa
- Authors: Chalmers, Russell
- Date: 2003
- Subjects: Polychaeta -- South Africa , Sabellidae -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5291 , http://hdl.handle.net/10962/d1005136 , Polychaeta -- South Africa , Sabellidae -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Description: Since the discovery of a new species of sabellid worm in 1993, the Californian and South African abalone industries have experienced increasing shell breakage and reduced growth rates of abalone, resulting in reduced market value of product. This polychaete worm can reach very high infestation levels. It was described as Terebrasabella heterouncinata in 1999, having originated from the South African coastline where it had been observed on several wild mollusc species. Although not a shell borer, it occupies tubes on the growing edge which are formed by deposition of nacreous shell over sabellid larvae by the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. Past research methods have not been successful in establishing effective means of eradication or control, partly due to the lack of knowledge of basic biological information on this species. This study forms the first part of an ongoing research project into the biology of terebrasabella heterouncinata. Abalone farms in South African utilise two main diets in abalone culture. An artificial formulated feed, Abfeed, is produced in South Africa and is used by the majority of farms as it increases abalone growth rate. Kelp, a natural diet of abalone, is harvested and also used as a feed. Farmers have observed higher sabellid infestation levels on Abfeed-fed abalone and suspect that diet may be an important factor influencing sabellid infestation. Abalone stocking density has also been identified as a potential factor influencing sabellid population growth on commercial farms. In order to better understand sabellid nutrition, the feeding behaviour of the sabellid in response to suspended solids of various particle size classes from both abalone diets were investigated. Both the effect of abalone diet and stocking density and their effects on sabellid morphometrics were quantified. The proximate composition and particle size distribution of suspended-solids present within kelp and Abfeed abalone raceways were also quantified. Results indicate that sabellid feeding follows no structured behavioural pattern for both abalone diets. The quantity of suspended solids in kelp raceways was greater than in Abfeed raceways (p<0.02) while there was no difference in particulate level between three abalone stocking densities (p>0.05). Protein (p<0.0001) and energy (p<0.0.1) levels of suspended solids were significantly greater in raceways dedicated to feeding Abfeed. The infestation level (number of tubes/centimetre on the grwoing edge) was significantly higher (p<0.001) in Abfeed-fed abalone. The morphometrics of the sabellids indicated that sabellids from Abfeed-fed abalone were larger in various body measurements: length (p<0.00001); neck width (p<0.001); base width (p<0.001); and surface area (p<0.001). This study suggests that abalone diet has an important influence on the infestation level and size of sabellids and that this is likely to be due to the fragmentation and leaching of nutrients from the artificially enriched commercial abalone diet.
- Full Text:
- Date Issued: 2003
- Authors: Chalmers, Russell
- Date: 2003
- Subjects: Polychaeta -- South Africa , Sabellidae -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5291 , http://hdl.handle.net/10962/d1005136 , Polychaeta -- South Africa , Sabellidae -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Description: Since the discovery of a new species of sabellid worm in 1993, the Californian and South African abalone industries have experienced increasing shell breakage and reduced growth rates of abalone, resulting in reduced market value of product. This polychaete worm can reach very high infestation levels. It was described as Terebrasabella heterouncinata in 1999, having originated from the South African coastline where it had been observed on several wild mollusc species. Although not a shell borer, it occupies tubes on the growing edge which are formed by deposition of nacreous shell over sabellid larvae by the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. Past research methods have not been successful in establishing effective means of eradication or control, partly due to the lack of knowledge of basic biological information on this species. This study forms the first part of an ongoing research project into the biology of terebrasabella heterouncinata. Abalone farms in South African utilise two main diets in abalone culture. An artificial formulated feed, Abfeed, is produced in South Africa and is used by the majority of farms as it increases abalone growth rate. Kelp, a natural diet of abalone, is harvested and also used as a feed. Farmers have observed higher sabellid infestation levels on Abfeed-fed abalone and suspect that diet may be an important factor influencing sabellid infestation. Abalone stocking density has also been identified as a potential factor influencing sabellid population growth on commercial farms. In order to better understand sabellid nutrition, the feeding behaviour of the sabellid in response to suspended solids of various particle size classes from both abalone diets were investigated. Both the effect of abalone diet and stocking density and their effects on sabellid morphometrics were quantified. The proximate composition and particle size distribution of suspended-solids present within kelp and Abfeed abalone raceways were also quantified. Results indicate that sabellid feeding follows no structured behavioural pattern for both abalone diets. The quantity of suspended solids in kelp raceways was greater than in Abfeed raceways (p<0.02) while there was no difference in particulate level between three abalone stocking densities (p>0.05). Protein (p<0.0001) and energy (p<0.0.1) levels of suspended solids were significantly greater in raceways dedicated to feeding Abfeed. The infestation level (number of tubes/centimetre on the grwoing edge) was significantly higher (p<0.001) in Abfeed-fed abalone. The morphometrics of the sabellids indicated that sabellids from Abfeed-fed abalone were larger in various body measurements: length (p<0.00001); neck width (p<0.001); base width (p<0.001); and surface area (p<0.001). This study suggests that abalone diet has an important influence on the infestation level and size of sabellids and that this is likely to be due to the fragmentation and leaching of nutrients from the artificially enriched commercial abalone diet.
- Full Text:
- Date Issued: 2003
Bioaccumulation and histopathology of copper in Oreochromis mossambicus
- Authors: Naigaga, Irene
- Date: 2003
- Subjects: Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5234 , http://hdl.handle.net/10962/d1005077 , Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
- Description: Cu is one of the most toxic elements that affect fish populations when the fish are exposed to concentrations exceeding their tolerance. To investigate the effects of elementary Cu on aspects of bioconcentration, histology and behaviour, O. mossambicus were exposed to 0 and 0.75 ± 0.20 mg/l of Cu for 96 hours (short-term study), and 0, 0.11 ± 0.02, 0.29 ± 0.02, and 0.47 ± 0.04 mg/l of Cu for 64 days (longterm study) under controlled conditions in the laboratory. For the long-term study fish were sampled for gills, liver, and kidney Cu accumulation analysis after 1, 32 and 64 days of exposure and after 1, 2, 4, 16, 32, and 64 days for gills, liver and spleen histology analysis. Cu accumulation was concentration-duration dependent with the highest accumulation capacity in the liver. A multifactor linear model was developed for the relationship between exposure dose, exposure duration and Cu accumulation in the organs with the liver model: Log L = 3.35 + 0.85W + 0.31T (r² = 0.892) giving a better fit than the gills: G = −35.09 + 10.58W + 17.58T (r² = 0.632). Where L = Cu accumulation values in the liver, G = Cu accumulation values in the gills (both in μg/g dry mass); W = exposure dose in water (mg/l); and T = exposure time (days). Using this model Cu accumulation in organs can be estimated when exposure concentration and duration is known. This model should be tested under different conditions to determine the potential of the model in monitoring Cu toxicity in the environment. Lesions were observed in the liver, gills and spleen in all Cu treatments at all exposure concentration and exposure durations. However, the incidence and the degree of alteration was related to the concentration of Cu and duration of exposure. The sequential appearance of lesions in the order of, hepatic vacuolar degeneration, fatty degeneration and necrosis indicated a gradual increase in liver damage with larger duration of exposure time and increasing Cu concentration. The initial lesions in the gills were manifested as hypertrophy and hyperplasia of the gill epithelium causing increase in the thickness of the secondary lamellae, mucous cell hypertrophy and proliferation, mucous hypersecretion, proliferation of eosinophilic granule cells and hyperplasia of interlamellar cells. With increase in exposure time, necrosis of the eosinophilic granule cells, lamellar oedema, epithelial desquamation and increase in severity of lamellar hyperplasia were observed. These lesions indicated an initial defence mechanism of the fish against Cu toxicity followed by advanced histological changes that were related to Cu concentration and duration of exposure. Changes in the spleen were haemosiderosis, increase in the white pulp and macrophage centres, reduction in the red pulp, and necrosis suggesting that fish exposed to environmentally relevant levels of Cu may be histopathologically altered leading to anaemia and immunosuppression. Regression analysis was used to quantify the relationship between the total activity of the fish, and duration of exposure. There was a gradual decline in fish activity related to Cu concentration and duration of exposure before introducing food into the tanks. There was a constant activity after introducing food in the tanks at the control and 0.11 ± 0.02 mg/l Cu exposure levels irrespective of exposure time. Analysis of covariance (ANCOVA) was used to test for the difference in slopes between treatments. There was no significant difference (p > 0.05) between slopes of the control and 0.11 ± 0.02 mg/l Cu, and between 0.29 ± 0.02 and 47 ± 0.04 mg/l Cu before and after introducing food in the tanks. The slopes of both the control and 0.11 ± 0.02 mg/l Cu were significantly different from those of 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu (p < 0.05). There were significant differences in the mean opercular movements per minute between treatments (p < 0.05). There was hyperventilation at 0.11 ± 0.02 mg/l Cu i.e. 87 ± 18 opercular movements per minute (mean ± standard deviation) and hypoventilation at 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu i.e. 37 ± 34 and 13 ± 6 opercular movements per minute compared to the control. Hypo- and hyperventilation were related to the lesser and greater gill damage, respectively. In conclusion Cu accumulation and effects on histology of the liver, gills and were related to the concentration of Cu in the water and duration of exposure showing a gradual increase in incidence and intensity with larger duration of exposure time and increasing Cu concentration. The fish were initially able to homeostatically regulate and detoxify Cu. However, as the exposure continued, the homeostatic mechanism appears to have failed to cope with the increasing metal burden causing advanced histological changes.
- Full Text:
- Date Issued: 2003
- Authors: Naigaga, Irene
- Date: 2003
- Subjects: Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5234 , http://hdl.handle.net/10962/d1005077 , Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
- Description: Cu is one of the most toxic elements that affect fish populations when the fish are exposed to concentrations exceeding their tolerance. To investigate the effects of elementary Cu on aspects of bioconcentration, histology and behaviour, O. mossambicus were exposed to 0 and 0.75 ± 0.20 mg/l of Cu for 96 hours (short-term study), and 0, 0.11 ± 0.02, 0.29 ± 0.02, and 0.47 ± 0.04 mg/l of Cu for 64 days (longterm study) under controlled conditions in the laboratory. For the long-term study fish were sampled for gills, liver, and kidney Cu accumulation analysis after 1, 32 and 64 days of exposure and after 1, 2, 4, 16, 32, and 64 days for gills, liver and spleen histology analysis. Cu accumulation was concentration-duration dependent with the highest accumulation capacity in the liver. A multifactor linear model was developed for the relationship between exposure dose, exposure duration and Cu accumulation in the organs with the liver model: Log L = 3.35 + 0.85W + 0.31T (r² = 0.892) giving a better fit than the gills: G = −35.09 + 10.58W + 17.58T (r² = 0.632). Where L = Cu accumulation values in the liver, G = Cu accumulation values in the gills (both in μg/g dry mass); W = exposure dose in water (mg/l); and T = exposure time (days). Using this model Cu accumulation in organs can be estimated when exposure concentration and duration is known. This model should be tested under different conditions to determine the potential of the model in monitoring Cu toxicity in the environment. Lesions were observed in the liver, gills and spleen in all Cu treatments at all exposure concentration and exposure durations. However, the incidence and the degree of alteration was related to the concentration of Cu and duration of exposure. The sequential appearance of lesions in the order of, hepatic vacuolar degeneration, fatty degeneration and necrosis indicated a gradual increase in liver damage with larger duration of exposure time and increasing Cu concentration. The initial lesions in the gills were manifested as hypertrophy and hyperplasia of the gill epithelium causing increase in the thickness of the secondary lamellae, mucous cell hypertrophy and proliferation, mucous hypersecretion, proliferation of eosinophilic granule cells and hyperplasia of interlamellar cells. With increase in exposure time, necrosis of the eosinophilic granule cells, lamellar oedema, epithelial desquamation and increase in severity of lamellar hyperplasia were observed. These lesions indicated an initial defence mechanism of the fish against Cu toxicity followed by advanced histological changes that were related to Cu concentration and duration of exposure. Changes in the spleen were haemosiderosis, increase in the white pulp and macrophage centres, reduction in the red pulp, and necrosis suggesting that fish exposed to environmentally relevant levels of Cu may be histopathologically altered leading to anaemia and immunosuppression. Regression analysis was used to quantify the relationship between the total activity of the fish, and duration of exposure. There was a gradual decline in fish activity related to Cu concentration and duration of exposure before introducing food into the tanks. There was a constant activity after introducing food in the tanks at the control and 0.11 ± 0.02 mg/l Cu exposure levels irrespective of exposure time. Analysis of covariance (ANCOVA) was used to test for the difference in slopes between treatments. There was no significant difference (p > 0.05) between slopes of the control and 0.11 ± 0.02 mg/l Cu, and between 0.29 ± 0.02 and 47 ± 0.04 mg/l Cu before and after introducing food in the tanks. The slopes of both the control and 0.11 ± 0.02 mg/l Cu were significantly different from those of 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu (p < 0.05). There were significant differences in the mean opercular movements per minute between treatments (p < 0.05). There was hyperventilation at 0.11 ± 0.02 mg/l Cu i.e. 87 ± 18 opercular movements per minute (mean ± standard deviation) and hypoventilation at 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu i.e. 37 ± 34 and 13 ± 6 opercular movements per minute compared to the control. Hypo- and hyperventilation were related to the lesser and greater gill damage, respectively. In conclusion Cu accumulation and effects on histology of the liver, gills and were related to the concentration of Cu in the water and duration of exposure showing a gradual increase in incidence and intensity with larger duration of exposure time and increasing Cu concentration. The fish were initially able to homeostatically regulate and detoxify Cu. However, as the exposure continued, the homeostatic mechanism appears to have failed to cope with the increasing metal burden causing advanced histological changes.
- Full Text:
- Date Issued: 2003
Biogeography and community structure of fishes in South African estuaries
- Authors: Harrison, Trevor D
- Date: 2003
- Subjects: Estuarine ecology -- South Africa Estuarine fishes -- South Africa Fish communities -- South Africa Biogeography -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5235 , http://hdl.handle.net/10962/d1005078
- Description: The biogeography and community structure of the fishes of South African estuaries was investigated. In all, 109 systems were examined representing two broad types: temporarily closed and permanently open estuaries. Multivariate analyses of the fish communities identified three biogeographic regions. A cool-temperate region extended along the west and southwest coasts; a warmtemperate zone stretched along the south, southeast and east coasts and a subtropical region occurred along the east coast. The boundaries of these biogeographic regions were also delineated. The general physico-chemical characteristics of the estuaries within the three biogeographic regions also reflected regional differences in climate, rainfall and ocean conditions. Estuarine temperatures followed the trend for marine coastal waters, decreasing from subtropical estuaries toward cool-temperate systems. The low rainfall and runoff in the warm-temperate region together with high evaporation rates and strong seawater input resulted in higher salinities in these estuaries. These factors also accounted for the predominantly clearer waters in warm-temperate estuaries. The estuaries in the three biogeographic regions were also shown to contain somewhat distinctive fish assemblages. Temperature and salinity appeared to be the two main factors affecting the distribution and abundance of fishes in South African estuaries. Subtropical systems were characterised by fishes mostly of tropical origin as well as certain south coast endemic species. Warm-temperate estuaries were dominated by endemic taxa with some tropical species also present. The fish fauna of cooltemperate estuaries mostly comprised south coast endemic species with cosmopolitan and temperate taxa also present. Certain functional components of the ichthyofauna also exhibited slight differences between regions. Freshwater fishes were a major component of closed subtropical estuaries while estuarine resident species were more abundant in warm-temperate estuaries. Overall, estuarine-dependent marine species dominated the fish fauna of the estuaries in all biogeographic regions, signifying that South African estuaries perform a vital nursery function for this group of fishes. Slight differences were also apparent in the trophic structure of the fishes; these were related to environmental differences between regions. Zooplanktivores and fishes that feed on aquatic macrophytes/invertebrates assumed a relatively higher importance in warm-temperate systems. Overall, detritivores dominated the estuarine fish fauna in all regions, indicating that detritus forms the main energy source in South African estuaries.
- Full Text:
- Date Issued: 2003
- Authors: Harrison, Trevor D
- Date: 2003
- Subjects: Estuarine ecology -- South Africa Estuarine fishes -- South Africa Fish communities -- South Africa Biogeography -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5235 , http://hdl.handle.net/10962/d1005078
- Description: The biogeography and community structure of the fishes of South African estuaries was investigated. In all, 109 systems were examined representing two broad types: temporarily closed and permanently open estuaries. Multivariate analyses of the fish communities identified three biogeographic regions. A cool-temperate region extended along the west and southwest coasts; a warmtemperate zone stretched along the south, southeast and east coasts and a subtropical region occurred along the east coast. The boundaries of these biogeographic regions were also delineated. The general physico-chemical characteristics of the estuaries within the three biogeographic regions also reflected regional differences in climate, rainfall and ocean conditions. Estuarine temperatures followed the trend for marine coastal waters, decreasing from subtropical estuaries toward cool-temperate systems. The low rainfall and runoff in the warm-temperate region together with high evaporation rates and strong seawater input resulted in higher salinities in these estuaries. These factors also accounted for the predominantly clearer waters in warm-temperate estuaries. The estuaries in the three biogeographic regions were also shown to contain somewhat distinctive fish assemblages. Temperature and salinity appeared to be the two main factors affecting the distribution and abundance of fishes in South African estuaries. Subtropical systems were characterised by fishes mostly of tropical origin as well as certain south coast endemic species. Warm-temperate estuaries were dominated by endemic taxa with some tropical species also present. The fish fauna of cooltemperate estuaries mostly comprised south coast endemic species with cosmopolitan and temperate taxa also present. Certain functional components of the ichthyofauna also exhibited slight differences between regions. Freshwater fishes were a major component of closed subtropical estuaries while estuarine resident species were more abundant in warm-temperate estuaries. Overall, estuarine-dependent marine species dominated the fish fauna of the estuaries in all biogeographic regions, signifying that South African estuaries perform a vital nursery function for this group of fishes. Slight differences were also apparent in the trophic structure of the fishes; these were related to environmental differences between regions. Zooplanktivores and fishes that feed on aquatic macrophytes/invertebrates assumed a relatively higher importance in warm-temperate systems. Overall, detritivores dominated the estuarine fish fauna in all regions, indicating that detritus forms the main energy source in South African estuaries.
- Full Text:
- Date Issued: 2003
Biology and demography of the spotted grunter Pomadasys commersonnii (Haemulidae) in South African waters
- Authors: Webb, Garth Anthony
- Date: 2003
- Subjects: Grunts (Fishes) -- South Africa , Grunts (Fishes) -- South Africa -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5201 , http://hdl.handle.net/10962/d1003727 , Grunts (Fishes) -- South Africa , Grunts (Fishes) -- South Africa -- Ecology
- Description: The spotted grunter, Pomadasys commersonnii (Haemulidae), is an Indian Ocean coastal species, extending from India to False Bay but is absent from the central Indian Ocean islands. Its taste and texture has made it one of the most important line fish species and is caught by recreational and subsistence fisherman along the entire east coast of South Africa. Because of its inshore distribution, reduced catch rates and estuarine dependence the species was de-commercialised in 1992. Since then it has been investigated as a candidate species for mariculture. All previous work on the biology of the species was undertaken on fish collected in KwaZulu-Natal in the mid 1970's. All other information has been incidental and formed part of other ecological studies. All management plans for this species have been based on these data. To develop a more comprehensive management plan that incorporates the entire population of spotted grunter, it was deemed necessary to reassess the biology (including feeding biology, age and growth and reproductive biology) as well as the demography of the population throughout its distributional range in South African waters. Analysis of the diet of spotted grunter, collected in estuaries, indicates that crustaceans form the bulk of the prey selected. Amphipods, mysids and estuarine brachyura predominate the diet of fish < 300 mm TL. At 200 mm TL fish start to prey on anomurans, which are extracted from their burrows using the 'blowing' feeding mechanism. Anomurans, in particular Upogebia africana and Callianassa krausii, become the preferred prey of fish larger than 300 mm TL. The high degree of diet flexibility that spotted grunter exhibit means that the composition and abundance of the macrobenthos of a particular environment will dictate the diet of the species. Otolith growth zones were found to be deposited annually with the opaque zones being deposited during the austral summer (November - February). The optical definition of annual otolith growth rings differed significantly between geographic regions (namely: Western Cape, South Eastern Cape and KwaZulu-Natal). Growth (sex combined) offish in the Western Cape were best described by the specialised 3 parameter Von Bertalanffy with a relative error structure in the form : Lt = 753(1- e⁻°·¹⁵⁴ ⁽t +¹·⁶¹⁵⁾) while growth in the South Eastern Cape was best described by using the Schnute model with an absolute error structure in the form: Lt=177°·⁴¹⁶ + (676.2⁻¹·²⁶⁶ - 169.2⁻¹²⁶⁶)[1-e°·⁴¹⁶⁽t-t₁⁾ / 1-e°·⁴¹⁶⁽t₂-t₁⁾]¹/¹·²⁶⁶ whereas growth was best described in KwaZulu-Natal using the specialised 3 parameter Von Bertalanffy with a relative error structure in the form: Lt = 839(1-e°·¹⁷⁽t⁺°·⁴⁹⁾) In the South Eastern Cape, length at 50% maturity was found to be 305 mm TL for males. Since females with ripe & running or spent gonads were not found in the South Eastern Cape and since histological evidence suggests that females in the South Eastern Cape have spawned, it appears that spawning does not occur in the South Eastern Cape. These results suggest that adults are resident in the estuaries of the Western and South Eastern Cape and undertake the spring/summer, northward spawning migration to KwaZulu-Natal. After joining the resident spawner stock in KwaZulu-Natal and spawning in the offshore environment of KwaZulu-Natal, adults soon return to the southern regions of their distributional range. Juveniles recruit into KwaZulu-Natal estuaries at a length of 25 - 35 mm TL. A proportion of the eggs and larvae are transported southwards along the periphery of the western boundary Agulhas Current where juveniles (25 - 30 mm TL) recruit into the estuaries as far south as the Swartvlei estuary in the Western Cape. There is evidence to suggest that the fish, which occur in the Western Cape estuaries, have migrated there once they have attained sexual maturity further east.
- Full Text:
- Date Issued: 2003
- Authors: Webb, Garth Anthony
- Date: 2003
- Subjects: Grunts (Fishes) -- South Africa , Grunts (Fishes) -- South Africa -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5201 , http://hdl.handle.net/10962/d1003727 , Grunts (Fishes) -- South Africa , Grunts (Fishes) -- South Africa -- Ecology
- Description: The spotted grunter, Pomadasys commersonnii (Haemulidae), is an Indian Ocean coastal species, extending from India to False Bay but is absent from the central Indian Ocean islands. Its taste and texture has made it one of the most important line fish species and is caught by recreational and subsistence fisherman along the entire east coast of South Africa. Because of its inshore distribution, reduced catch rates and estuarine dependence the species was de-commercialised in 1992. Since then it has been investigated as a candidate species for mariculture. All previous work on the biology of the species was undertaken on fish collected in KwaZulu-Natal in the mid 1970's. All other information has been incidental and formed part of other ecological studies. All management plans for this species have been based on these data. To develop a more comprehensive management plan that incorporates the entire population of spotted grunter, it was deemed necessary to reassess the biology (including feeding biology, age and growth and reproductive biology) as well as the demography of the population throughout its distributional range in South African waters. Analysis of the diet of spotted grunter, collected in estuaries, indicates that crustaceans form the bulk of the prey selected. Amphipods, mysids and estuarine brachyura predominate the diet of fish < 300 mm TL. At 200 mm TL fish start to prey on anomurans, which are extracted from their burrows using the 'blowing' feeding mechanism. Anomurans, in particular Upogebia africana and Callianassa krausii, become the preferred prey of fish larger than 300 mm TL. The high degree of diet flexibility that spotted grunter exhibit means that the composition and abundance of the macrobenthos of a particular environment will dictate the diet of the species. Otolith growth zones were found to be deposited annually with the opaque zones being deposited during the austral summer (November - February). The optical definition of annual otolith growth rings differed significantly between geographic regions (namely: Western Cape, South Eastern Cape and KwaZulu-Natal). Growth (sex combined) offish in the Western Cape were best described by the specialised 3 parameter Von Bertalanffy with a relative error structure in the form : Lt = 753(1- e⁻°·¹⁵⁴ ⁽t +¹·⁶¹⁵⁾) while growth in the South Eastern Cape was best described by using the Schnute model with an absolute error structure in the form: Lt=177°·⁴¹⁶ + (676.2⁻¹·²⁶⁶ - 169.2⁻¹²⁶⁶)[1-e°·⁴¹⁶⁽t-t₁⁾ / 1-e°·⁴¹⁶⁽t₂-t₁⁾]¹/¹·²⁶⁶ whereas growth was best described in KwaZulu-Natal using the specialised 3 parameter Von Bertalanffy with a relative error structure in the form: Lt = 839(1-e°·¹⁷⁽t⁺°·⁴⁹⁾) In the South Eastern Cape, length at 50% maturity was found to be 305 mm TL for males. Since females with ripe & running or spent gonads were not found in the South Eastern Cape and since histological evidence suggests that females in the South Eastern Cape have spawned, it appears that spawning does not occur in the South Eastern Cape. These results suggest that adults are resident in the estuaries of the Western and South Eastern Cape and undertake the spring/summer, northward spawning migration to KwaZulu-Natal. After joining the resident spawner stock in KwaZulu-Natal and spawning in the offshore environment of KwaZulu-Natal, adults soon return to the southern regions of their distributional range. Juveniles recruit into KwaZulu-Natal estuaries at a length of 25 - 35 mm TL. A proportion of the eggs and larvae are transported southwards along the periphery of the western boundary Agulhas Current where juveniles (25 - 30 mm TL) recruit into the estuaries as far south as the Swartvlei estuary in the Western Cape. There is evidence to suggest that the fish, which occur in the Western Cape estuaries, have migrated there once they have attained sexual maturity further east.
- Full Text:
- Date Issued: 2003
Intercohort cannibalism and parturition-associated behaviour of captive-bred swordtail, Xiphophorus helleri (Pisces: Poeciliidae)
- Jones, Clifford Louis Wilshire
- Authors: Jones, Clifford Louis Wilshire
- Date: 2003
- Subjects: Poeciliidae -- Behavior Xiphophorus helleri Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5351 , http://hdl.handle.net/10962/d1007812
- Description: Adult fish that belong to the family Poeciliidae cannibalise juveniles, both in the wild and under captive conditions, but this behaviour has only been partly investigated in the Poeciliidae in some of the commercially valuable species. The objective of the research is to develop an understanding of intercohort cannibalism and parturition-associated behaviour in captive-bred swordtail (Xiphophorus helleri), with applications to industry and future research of other poeciliids. Experiments investigating the effect of adult stocking density and sex ratio on the production of juveniles were used to determine if cannibalism occurs under culture conditions. The average rate of intercohort cannibalism ranged from (5.5 to 53.9%), and was positively density dependent and independent of sex ratio, indicating that males and females were probably equally cannibalistic. The highest number of juveniles (1725.7±141.4) produced per tank over 70 days was obtained from two males and eight females. To develop a better understanding of adult and juvenile behaviour during parturition, fish were observed under controlled laboratory conditions using video and behaviours such as attack (burst of speed by an adult in the direction of a juvenile), escape (avoidance of cannibalism after attack) and cannibalism (predation of a live juvenile by an adult), for example, were identified. Under laboratory conditions most young escaped in downward direction after attack (49%) and most utilised the refuge made that was made available. Furthermore, most attacks (62-65%) and cannibalism (57-84%) occurred at the bottom. Since the presence of refuge significantly increased the rate of juvenile survival under culture conditions, it was hypothesised that the rate of cannibalism could be reduced under farming conditions if juveniles were protected when they escaped downwards. This hypothesis was accepted as it was found that refuge at the bottom of the water column or the inclusion of a false-bottom reduced the rate of cannibalism by 49% and 72%, respectively. Similarly, the hypothesise that the rate of cannibalism could be reduced if juveniles where given protection when escaping sideways (32% of juveniles escaped sideways in the laboratory) was also accepted when tested under farm-scale conditions because a false-side reduced the rate of cannibalism by an average of 45%. Since males and females were equally responsible for cannibalising juveniles in the laboratory, it was hypothesised that the rate of cannibalism would decrease proportionately with the removal of males (Le. 20% of the cannibals) from the population; the removal of males under farming conditions resulted in a 19.5% reduction in the rate of cannibalism. Since older juveniles were better able to escape cannibalism than neonates and since adults habituate to stimuli that previously resulted in attack behaviour, it was hypothesised that the rate of cannibalism would remain unaffected by the length of time that juveniles were exposed to adults in the breeding tanks. This hypothesis was also accepted when tested under farm conditions. However, some hypotheses based on laboratory observations were not accepted. For example, a constant low light intensity did not appear to decrease the rate of cannibalism under farm conditions; also, the occurrence of dead and deformed juveniles went unnoticed in the laboratory, and under farm conditions, where adults did not have access to the bottom of the tank, 10% of the harvest consisted of dead and deformed juveniles. It is concluded that technologies, such as bottom-refuge or a false-side, that increase the size of the liveharvest and allow for the removal of potentially less viable offspring are recommended for the commercial production of poeciliids. The overall similarity of X. helleri behaviour between the laboratory experiments and the farm-scale trials suggests that the post-partum behaviour of X. helleri remains consistent under these different conditions; thus, behaviour under one set of conditions may be used to predict behaviour under other conditions. The application and significance of extrapolations to industry and future research of X. helleri and possibly other poeciliids were discussed and the most applicable laboratory observations with the highest extrapolation capacity were proposed. Furthermore, techniques were developed to aid industry and future researchers in making predictions relating to behaviour of X. helleri under different conditions based on laboratory observations. The results were used to develop a model indicating that selection pressures against cannibalism are not likely to exist at the rate of cannibalism observed here since the potential genetic gain through kin survival and inclusive fitness was shown to be greater than any potential genetiC loss experienced by a victim of cannibalism. The model was successfully tested under a range of social conditions. Other possible explanations for cannibalism in poeciliids, such as parental manipulation, nutritional advantages, opportunistic predation and the recovery of energy are discussed. It is suggested that the most likely proximate cause of cannibalism under captive conditions is opportunistic predation. The theory that cannibalism ensures that only viable genes of the victim are expressed, through inclusive fitness, is a possible ultimate cause of cannibalism, which may have been inherited from feral ancestors of captive-bred X. helleri.
- Full Text:
- Date Issued: 2003
- Authors: Jones, Clifford Louis Wilshire
- Date: 2003
- Subjects: Poeciliidae -- Behavior Xiphophorus helleri Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5351 , http://hdl.handle.net/10962/d1007812
- Description: Adult fish that belong to the family Poeciliidae cannibalise juveniles, both in the wild and under captive conditions, but this behaviour has only been partly investigated in the Poeciliidae in some of the commercially valuable species. The objective of the research is to develop an understanding of intercohort cannibalism and parturition-associated behaviour in captive-bred swordtail (Xiphophorus helleri), with applications to industry and future research of other poeciliids. Experiments investigating the effect of adult stocking density and sex ratio on the production of juveniles were used to determine if cannibalism occurs under culture conditions. The average rate of intercohort cannibalism ranged from (5.5 to 53.9%), and was positively density dependent and independent of sex ratio, indicating that males and females were probably equally cannibalistic. The highest number of juveniles (1725.7±141.4) produced per tank over 70 days was obtained from two males and eight females. To develop a better understanding of adult and juvenile behaviour during parturition, fish were observed under controlled laboratory conditions using video and behaviours such as attack (burst of speed by an adult in the direction of a juvenile), escape (avoidance of cannibalism after attack) and cannibalism (predation of a live juvenile by an adult), for example, were identified. Under laboratory conditions most young escaped in downward direction after attack (49%) and most utilised the refuge made that was made available. Furthermore, most attacks (62-65%) and cannibalism (57-84%) occurred at the bottom. Since the presence of refuge significantly increased the rate of juvenile survival under culture conditions, it was hypothesised that the rate of cannibalism could be reduced under farming conditions if juveniles were protected when they escaped downwards. This hypothesis was accepted as it was found that refuge at the bottom of the water column or the inclusion of a false-bottom reduced the rate of cannibalism by 49% and 72%, respectively. Similarly, the hypothesise that the rate of cannibalism could be reduced if juveniles where given protection when escaping sideways (32% of juveniles escaped sideways in the laboratory) was also accepted when tested under farm-scale conditions because a false-side reduced the rate of cannibalism by an average of 45%. Since males and females were equally responsible for cannibalising juveniles in the laboratory, it was hypothesised that the rate of cannibalism would decrease proportionately with the removal of males (Le. 20% of the cannibals) from the population; the removal of males under farming conditions resulted in a 19.5% reduction in the rate of cannibalism. Since older juveniles were better able to escape cannibalism than neonates and since adults habituate to stimuli that previously resulted in attack behaviour, it was hypothesised that the rate of cannibalism would remain unaffected by the length of time that juveniles were exposed to adults in the breeding tanks. This hypothesis was also accepted when tested under farm conditions. However, some hypotheses based on laboratory observations were not accepted. For example, a constant low light intensity did not appear to decrease the rate of cannibalism under farm conditions; also, the occurrence of dead and deformed juveniles went unnoticed in the laboratory, and under farm conditions, where adults did not have access to the bottom of the tank, 10% of the harvest consisted of dead and deformed juveniles. It is concluded that technologies, such as bottom-refuge or a false-side, that increase the size of the liveharvest and allow for the removal of potentially less viable offspring are recommended for the commercial production of poeciliids. The overall similarity of X. helleri behaviour between the laboratory experiments and the farm-scale trials suggests that the post-partum behaviour of X. helleri remains consistent under these different conditions; thus, behaviour under one set of conditions may be used to predict behaviour under other conditions. The application and significance of extrapolations to industry and future research of X. helleri and possibly other poeciliids were discussed and the most applicable laboratory observations with the highest extrapolation capacity were proposed. Furthermore, techniques were developed to aid industry and future researchers in making predictions relating to behaviour of X. helleri under different conditions based on laboratory observations. The results were used to develop a model indicating that selection pressures against cannibalism are not likely to exist at the rate of cannibalism observed here since the potential genetic gain through kin survival and inclusive fitness was shown to be greater than any potential genetiC loss experienced by a victim of cannibalism. The model was successfully tested under a range of social conditions. Other possible explanations for cannibalism in poeciliids, such as parental manipulation, nutritional advantages, opportunistic predation and the recovery of energy are discussed. It is suggested that the most likely proximate cause of cannibalism under captive conditions is opportunistic predation. The theory that cannibalism ensures that only viable genes of the victim are expressed, through inclusive fitness, is a possible ultimate cause of cannibalism, which may have been inherited from feral ancestors of captive-bred X. helleri.
- Full Text:
- Date Issued: 2003
Morphometrics and reproduction of Terebrasabella heterouncinata (Polychaeta:Sabellidae), infesting abalone (Haliotis midae) from different culture environments
- Authors: Gray, Michael
- Date: 2003
- Subjects: Polychaeta , Sabellidae , Abalones -- Physiology , Abalones -- Nutrition , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5384 , http://hdl.handle.net/10962/d1018231
- Description: In the late 1980's abalone culturalists noticed reduced growth rate and shell deformities in some abalone stocks. These problems were the result of infestations by a shell boring polychaete, Terebrasabella heterouncinata. Under intensive abalone culture conditions the level of infestation can reach epidemic proportions and there are often severe consequences for the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. This study formed part of an ongoing project that is aimed at investigating the basic biology of Terebrasabella heterouncinata. The majority of abalone farmers in South Africa feed their abalone either naturally occurring kelp (Ecklonia maxima) or the formulated abalone feed, Abfeed. Farmers have suggested that the use of Abfeed is associated with higher sabellid infestation levels and changing the abalone diet from Abfeed to kelp helps reduce sabellid infestation. Speculation has arisen indicating that older, slower growing abalone are more susceptible to sabellid infestation. The effect of host abalone diet history and their growth on sabellid settlement success, morphometries and reproduction was quantified. To better understand the plasticity of the expression of life history traits the variability of morphometric and reproductive characteristics was compared between different farm environments. And more...
- Full Text:
- Date Issued: 2003
- Authors: Gray, Michael
- Date: 2003
- Subjects: Polychaeta , Sabellidae , Abalones -- Physiology , Abalones -- Nutrition , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5384 , http://hdl.handle.net/10962/d1018231
- Description: In the late 1980's abalone culturalists noticed reduced growth rate and shell deformities in some abalone stocks. These problems were the result of infestations by a shell boring polychaete, Terebrasabella heterouncinata. Under intensive abalone culture conditions the level of infestation can reach epidemic proportions and there are often severe consequences for the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. This study formed part of an ongoing project that is aimed at investigating the basic biology of Terebrasabella heterouncinata. The majority of abalone farmers in South Africa feed their abalone either naturally occurring kelp (Ecklonia maxima) or the formulated abalone feed, Abfeed. Farmers have suggested that the use of Abfeed is associated with higher sabellid infestation levels and changing the abalone diet from Abfeed to kelp helps reduce sabellid infestation. Speculation has arisen indicating that older, slower growing abalone are more susceptible to sabellid infestation. The effect of host abalone diet history and their growth on sabellid settlement success, morphometries and reproduction was quantified. To better understand the plasticity of the expression of life history traits the variability of morphometric and reproductive characteristics was compared between different farm environments. And more...
- Full Text:
- Date Issued: 2003
On the use of metabolic rate measurements to assess the stress response in juvenile spotted grunter, Pomadasys commersonnii (Haemulidae, Pisces)
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
The potential of abalone stock enhancement in the Eastern Cape Province of South Africa
- Authors: Godfrey, Brian Peter
- Date: 2003
- Subjects: Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5312 , http://hdl.handle.net/10962/d1005157 , Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Description: The largest abalone in South Africa, the perlemoen, Haliotis midae, occurs along approximately two-thirds of the country's coastline, but has only been the target of an extensive commercial fishery in the south-western part of South Africa. Large-scale illegal fishing has however proliferated throughout its entire range over the last 10–15 years, which has had serious effects on stock abundance and once productive populations are facing economic collapse. Abalone stock enhancement has been put forward as an addition or alternative to traditional fisheries management practices, which can potentially rehabilitate overfished abalone populations and enhance natural production. The aim of this project was to investigate the potential of abalone stock enhancement for managing an area in the Eastern Cape Province, which was being subjected to intense illegal fishing pressure. A research approach was adopted to investigate the scale and effects of this poaching and to investigate the survival of artificially cultured abalone seed in the natural environment. A model of a commercial-scale ranching operation was investigated to assess the economic feasibility of such a scheme. Analysis of poaching cases and research samples from Cape Recife indicated high levels of fishing effort that appeared to be causing the observed declines in emergent abalone abundance and average size. Poaching cases from Cape Recife contributed 32% of the total number of cases of known origin in the Eastern Cape Province from 1998–2002, with the majority of the cases (82%) originating from within the Port Elizabeth metropole. There was an exponential increase in the number of poaching cases in the Eastern Cape Province (r²=0.967) and Port Elizabeth over this period but actual annual total catch stabilized, particularly at Cape Recife, where estimates of CPUE declined significantly from 2000–2002 (p<0.001). The annual proportion of emergent abalone under the MLS from Cape Recife was always >85% in confiscations and research collections, and did not change significantly over the period of examination. Comparison of illegal catches with an adjacent site indicated that the emergent abalone population at Cape Recife had a significantly higher proportion of undersized emergent animals (p<0.001) and they were significantly smaller than the abalone from the closest site, Noordhoek, and other areas in Port Elizabeth from 2000–2002 (p<0.001). The apparent declines in emergent abalone abundance indicated by the poaching data were corroborated by sampling of emergent abalone abundance at Cape Recife. Numbers of abalone declined significantly from 125.6 to 53.8 per 20min count (p<0.001), from April 1998–October 2001 and density declined from 1.3 to 0.8m⁻² over a similar period (p<0.001). Juvenile density did not change over this period, although there were significant differences in density observed between two different habitats (p<0.001). Initial releases of cultured juvenile abalone showed that they could be distinguished from their wild counterparts for at least a year after release, by their different shell colouration. Short-term, small-scale trials (7–10 days) using animals between 17 and 30mm SL had mean survival rates of 64–82% (mean 70.4%) and the effect of size on survival was not significant in most cases, although the power to detect differences was low. Attempts to measure the effect of habitat on survival were not conclusive, although refuges under sea urchins appeared to be favoured by both seed and wild abalone, although urchins were not an absolute requirement for survival. Similar medium-term trials (31–74 days) in sheltered sites yielded mean returns of 53.1% using 25mm SL animals and similar trials in a more exposed area had more variable survival rates of between 18.4 and 73.6%, after 25–27 days. A comparison between careful hand-seeding and surface-scattering seed release methods in the open-ocean habitat showed no significant differences in survival rate after 41 days. Larger seed survived significantly better than the smaller seed when scattered on the surface (p<0.0001) and the smaller seed survived significantly better when seeded carefully by hand onto the substrate (p<0.028). Further medium-term releases of large numbers of seed abalone, released using the surface-scattering method in open-ocean habitat, gave mean survival rates of 32.8% over periods of 83–114 days. Assessment of a seeding trial using release modules to seed juvenile animals in the open-ocean was hampered by poor sea conditions and difficult to search substrates, and a mean recovery rate of 3.1% was obtained for the sites that were sampled. Movement of seed was low in the more sheltered sites, and also appeared to be affected by the amount of available habitat. Growth of seed was measured using changes in shell colouration and there were significant differences between areas. An average growth of 1.6mm.month⁻¹ shell length was calculated for all areas. The potential for commercial scale abalone ranching to be used to enhance a territorial user right fishery was investigated using a model of economic feasibility. Internal rates of return of 30.3 and 36.9% were obtained from two harvest regimes using different harvest sizes. There was a high degree of risk associated with these figures owing to a lack of consistent seed survival rate estimates, and the input parameters, which are subject to variation, showed a significant effect on profitability. The operation of this type of ranching scheme is probably not economically feasible as a stand-alone operation but could probably be operated effectively in conjunction with an existing abalone farm. By adding a small wild catch component the profitability of a ranching scheme could be significantly improved. The results of the present study indicate that high levels of poaching at Cape Recife have led to declines in emergent abalone abundance, which will probably lead to stock collapse in the near future. This implies that fisheries managers have failed to fulfil the provisions of fisheries policy in South Africa. The present results from seeding trials show that cultured juveniles can survive and make a contribution to overall stock abundance. Furthermore, while there are obstacles to economic feasibility, commercial ranching has the potential to be a valuable addition to current abalone management strategy.
- Full Text:
- Date Issued: 2003
- Authors: Godfrey, Brian Peter
- Date: 2003
- Subjects: Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5312 , http://hdl.handle.net/10962/d1005157 , Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Description: The largest abalone in South Africa, the perlemoen, Haliotis midae, occurs along approximately two-thirds of the country's coastline, but has only been the target of an extensive commercial fishery in the south-western part of South Africa. Large-scale illegal fishing has however proliferated throughout its entire range over the last 10–15 years, which has had serious effects on stock abundance and once productive populations are facing economic collapse. Abalone stock enhancement has been put forward as an addition or alternative to traditional fisheries management practices, which can potentially rehabilitate overfished abalone populations and enhance natural production. The aim of this project was to investigate the potential of abalone stock enhancement for managing an area in the Eastern Cape Province, which was being subjected to intense illegal fishing pressure. A research approach was adopted to investigate the scale and effects of this poaching and to investigate the survival of artificially cultured abalone seed in the natural environment. A model of a commercial-scale ranching operation was investigated to assess the economic feasibility of such a scheme. Analysis of poaching cases and research samples from Cape Recife indicated high levels of fishing effort that appeared to be causing the observed declines in emergent abalone abundance and average size. Poaching cases from Cape Recife contributed 32% of the total number of cases of known origin in the Eastern Cape Province from 1998–2002, with the majority of the cases (82%) originating from within the Port Elizabeth metropole. There was an exponential increase in the number of poaching cases in the Eastern Cape Province (r²=0.967) and Port Elizabeth over this period but actual annual total catch stabilized, particularly at Cape Recife, where estimates of CPUE declined significantly from 2000–2002 (p<0.001). The annual proportion of emergent abalone under the MLS from Cape Recife was always >85% in confiscations and research collections, and did not change significantly over the period of examination. Comparison of illegal catches with an adjacent site indicated that the emergent abalone population at Cape Recife had a significantly higher proportion of undersized emergent animals (p<0.001) and they were significantly smaller than the abalone from the closest site, Noordhoek, and other areas in Port Elizabeth from 2000–2002 (p<0.001). The apparent declines in emergent abalone abundance indicated by the poaching data were corroborated by sampling of emergent abalone abundance at Cape Recife. Numbers of abalone declined significantly from 125.6 to 53.8 per 20min count (p<0.001), from April 1998–October 2001 and density declined from 1.3 to 0.8m⁻² over a similar period (p<0.001). Juvenile density did not change over this period, although there were significant differences in density observed between two different habitats (p<0.001). Initial releases of cultured juvenile abalone showed that they could be distinguished from their wild counterparts for at least a year after release, by their different shell colouration. Short-term, small-scale trials (7–10 days) using animals between 17 and 30mm SL had mean survival rates of 64–82% (mean 70.4%) and the effect of size on survival was not significant in most cases, although the power to detect differences was low. Attempts to measure the effect of habitat on survival were not conclusive, although refuges under sea urchins appeared to be favoured by both seed and wild abalone, although urchins were not an absolute requirement for survival. Similar medium-term trials (31–74 days) in sheltered sites yielded mean returns of 53.1% using 25mm SL animals and similar trials in a more exposed area had more variable survival rates of between 18.4 and 73.6%, after 25–27 days. A comparison between careful hand-seeding and surface-scattering seed release methods in the open-ocean habitat showed no significant differences in survival rate after 41 days. Larger seed survived significantly better than the smaller seed when scattered on the surface (p<0.0001) and the smaller seed survived significantly better when seeded carefully by hand onto the substrate (p<0.028). Further medium-term releases of large numbers of seed abalone, released using the surface-scattering method in open-ocean habitat, gave mean survival rates of 32.8% over periods of 83–114 days. Assessment of a seeding trial using release modules to seed juvenile animals in the open-ocean was hampered by poor sea conditions and difficult to search substrates, and a mean recovery rate of 3.1% was obtained for the sites that were sampled. Movement of seed was low in the more sheltered sites, and also appeared to be affected by the amount of available habitat. Growth of seed was measured using changes in shell colouration and there were significant differences between areas. An average growth of 1.6mm.month⁻¹ shell length was calculated for all areas. The potential for commercial scale abalone ranching to be used to enhance a territorial user right fishery was investigated using a model of economic feasibility. Internal rates of return of 30.3 and 36.9% were obtained from two harvest regimes using different harvest sizes. There was a high degree of risk associated with these figures owing to a lack of consistent seed survival rate estimates, and the input parameters, which are subject to variation, showed a significant effect on profitability. The operation of this type of ranching scheme is probably not economically feasible as a stand-alone operation but could probably be operated effectively in conjunction with an existing abalone farm. By adding a small wild catch component the profitability of a ranching scheme could be significantly improved. The results of the present study indicate that high levels of poaching at Cape Recife have led to declines in emergent abalone abundance, which will probably lead to stock collapse in the near future. This implies that fisheries managers have failed to fulfil the provisions of fisheries policy in South Africa. The present results from seeding trials show that cultured juveniles can survive and make a contribution to overall stock abundance. Furthermore, while there are obstacles to economic feasibility, commercial ranching has the potential to be a valuable addition to current abalone management strategy.
- Full Text:
- Date Issued: 2003
A description of spatial and temporal aspects of the lifecycle of chokka squid Loligo vulgaris reynaudii on the inshore spawning grounds and Agulhas bank off the South Coast of South Africa
- Authors: Olyott, Leonard James Henry
- Date: 2002
- Subjects: Squids -- South Africa , Loliginidae -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5253 , http://hdl.handle.net/10962/d1005096 , Squids -- South Africa , Loliginidae -- South Africa
- Description: The chokka squid, Loligo vulgaris reynaudii, is a commercially important species supporting a large, high-value export fishery for South Africa. This study reviewed its population dynamics and reproductive biology. Biological information collected on biannual research cruises from September 1986 to April 1999 on the Agulhas Bank as well as information from commercial vessels operating in the inshore environment collected between April 1988 and July 1989 and again between June 1999 and May 2000 were analysed. Size ranges of juveniles, subadults and adults were calculated and used to determine seasonal distribution and abundance patterns. Based on Gonadosomatic Indices (GSI) and percentages of mature squid in each month, two peak reproductive seasons in summer and winter were identified although mature squid were present all year round. Seasonal peaks in sex ratio were also apparent with males outnumbering females by up to 4:1 in the peak-breeding season. The size at which squid matured, demonstrated both spatial and temporal patterns. Squid caught in spring matured at a smaller size than squid caught in autumn and at successively smaller sizes from west to east across the Agulhas Bank. Size at maturity was highly variable especially in males where “sneaker males” were evident in both seasons. Length-to-weight linear regression revealed significant differences between maturity stages and between sexes. Females demonstrated steeper length-to-weight regression slopes than males in the peak-breeding seasons. Aspects of squid biology pertinent to fishery management were highlighted as well as potential areas where research should be directed in order to develop future stock assessment models.
- Full Text:
- Date Issued: 2002
- Authors: Olyott, Leonard James Henry
- Date: 2002
- Subjects: Squids -- South Africa , Loliginidae -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5253 , http://hdl.handle.net/10962/d1005096 , Squids -- South Africa , Loliginidae -- South Africa
- Description: The chokka squid, Loligo vulgaris reynaudii, is a commercially important species supporting a large, high-value export fishery for South Africa. This study reviewed its population dynamics and reproductive biology. Biological information collected on biannual research cruises from September 1986 to April 1999 on the Agulhas Bank as well as information from commercial vessels operating in the inshore environment collected between April 1988 and July 1989 and again between June 1999 and May 2000 were analysed. Size ranges of juveniles, subadults and adults were calculated and used to determine seasonal distribution and abundance patterns. Based on Gonadosomatic Indices (GSI) and percentages of mature squid in each month, two peak reproductive seasons in summer and winter were identified although mature squid were present all year round. Seasonal peaks in sex ratio were also apparent with males outnumbering females by up to 4:1 in the peak-breeding season. The size at which squid matured, demonstrated both spatial and temporal patterns. Squid caught in spring matured at a smaller size than squid caught in autumn and at successively smaller sizes from west to east across the Agulhas Bank. Size at maturity was highly variable especially in males where “sneaker males” were evident in both seasons. Length-to-weight linear regression revealed significant differences between maturity stages and between sexes. Females demonstrated steeper length-to-weight regression slopes than males in the peak-breeding seasons. Aspects of squid biology pertinent to fishery management were highlighted as well as potential areas where research should be directed in order to develop future stock assessment models.
- Full Text:
- Date Issued: 2002
An analysis of the trawl and longline fisheries for Merluccius capensis off the west coast of South Africa
- Authors: Fairweather, Tracey Pamela
- Date: 2002
- Subjects: Fisheries -- South Africa , Merluccius capensis -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5218 , http://hdl.handle.net/10962/d1005061 , Fisheries -- South Africa , Merluccius capensis -- South Africa
- Description: The South African hake resource faces divergent fishing pressures and management issues. Although the resource consists of two species, management was simplified because the resource was only subject to trawl effort and because of the similarity in population parameters, single species assessment models could be adopted. The impact of trawling on the stock is considered to be well understood and the resource has shown recovery since exclusion of foreign vessels. The 1990s were punctuated by major political change and the need for transformation has resulted in an expansion of the number of fishing rights holders. Longlining has been reintroduced and there is no clear understanding of how the combined fishing pressures will affect the population structure of either Merluccius capensis or M. paradoxus. Information is vital to successful management. Fisheries are complex and intricate, and at times appear impossible to control or monitor. An integrated information system provides easily understood graphical explanations of complex issues. This thesis assessed the dynamics of the trawl and longline fisheries between 1994 and 1999 using a geographical information system (GIS). The accessability of a GIS incorporates the needs of scientists, managers and fishing communities. The simple GIS developed in this study revealed shifts in effort, facilitated the calculation of spatially precise catches and biomasses and highlighted the inadequacy of current sampling coverage. Trawlers were shown to fish the same areas consistently during the years investigated, with highest fishing intensity and average CPUE achieved at depths between 300 and 500m. Analysis of the longline sector revealed several similarities to the trawl sector, fishing intensity was highest between 301 and 500m, suggesting that both sectors face a "friction of distance" dilemma. The distribution and abundance of hake, in particular the exploitable proportion of the population, was determined by a combination of depth and substrate type. The selectivity patterns of trawlers and longliners were briefly investigated with the results illustrating that gear selectivity of the M. capensis stock was depth dependent. The deeper fishing occurred, the larger the length-at-selection. As a result, the M. capensis parental stock faces unprecedented fishing pressure. In the absence of reliable species-specific catch data, logistic and linear regression models were developed to split the hake catch into its respective species components. Large discrepancies between the predicted M. capensis catch for the two models were noted. Regression estimates constructed at a finer spatial scale may provide a better fit than the current depth logistic employed by Marine and Coastal Management. A first attempt at assessing the M. capensis resource on the West Coast using an age-structured production model was presented. It was found that a lengthy and accurate M. capensis catch series is required before it is possible to successfully model the dynamics of the stock. It is necessary to incorporate finer spatial detail in the collation of catch data and collection of sampling data. It would be unadvisable to assume that the stock is stable or recovering. The implications of a size/sex relationship must be investigated and properly appraised.
- Full Text:
- Date Issued: 2002
- Authors: Fairweather, Tracey Pamela
- Date: 2002
- Subjects: Fisheries -- South Africa , Merluccius capensis -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5218 , http://hdl.handle.net/10962/d1005061 , Fisheries -- South Africa , Merluccius capensis -- South Africa
- Description: The South African hake resource faces divergent fishing pressures and management issues. Although the resource consists of two species, management was simplified because the resource was only subject to trawl effort and because of the similarity in population parameters, single species assessment models could be adopted. The impact of trawling on the stock is considered to be well understood and the resource has shown recovery since exclusion of foreign vessels. The 1990s were punctuated by major political change and the need for transformation has resulted in an expansion of the number of fishing rights holders. Longlining has been reintroduced and there is no clear understanding of how the combined fishing pressures will affect the population structure of either Merluccius capensis or M. paradoxus. Information is vital to successful management. Fisheries are complex and intricate, and at times appear impossible to control or monitor. An integrated information system provides easily understood graphical explanations of complex issues. This thesis assessed the dynamics of the trawl and longline fisheries between 1994 and 1999 using a geographical information system (GIS). The accessability of a GIS incorporates the needs of scientists, managers and fishing communities. The simple GIS developed in this study revealed shifts in effort, facilitated the calculation of spatially precise catches and biomasses and highlighted the inadequacy of current sampling coverage. Trawlers were shown to fish the same areas consistently during the years investigated, with highest fishing intensity and average CPUE achieved at depths between 300 and 500m. Analysis of the longline sector revealed several similarities to the trawl sector, fishing intensity was highest between 301 and 500m, suggesting that both sectors face a "friction of distance" dilemma. The distribution and abundance of hake, in particular the exploitable proportion of the population, was determined by a combination of depth and substrate type. The selectivity patterns of trawlers and longliners were briefly investigated with the results illustrating that gear selectivity of the M. capensis stock was depth dependent. The deeper fishing occurred, the larger the length-at-selection. As a result, the M. capensis parental stock faces unprecedented fishing pressure. In the absence of reliable species-specific catch data, logistic and linear regression models were developed to split the hake catch into its respective species components. Large discrepancies between the predicted M. capensis catch for the two models were noted. Regression estimates constructed at a finer spatial scale may provide a better fit than the current depth logistic employed by Marine and Coastal Management. A first attempt at assessing the M. capensis resource on the West Coast using an age-structured production model was presented. It was found that a lengthy and accurate M. capensis catch series is required before it is possible to successfully model the dynamics of the stock. It is necessary to incorporate finer spatial detail in the collation of catch data and collection of sampling data. It would be unadvisable to assume that the stock is stable or recovering. The implications of a size/sex relationship must be investigated and properly appraised.
- Full Text:
- Date Issued: 2002
Dynamics of early stage fishes associated with selected warm temperate estuaries in South Africa
- Authors: Strydom, Nadine Amelia
- Date: 2002
- Subjects: Estuarine fishes -- South Africa Fishes -- Infancy -- South Africa Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5262 , http://hdl.handle.net/10962/d1005106
- Description: Early stage fishes, namely larvae and early juveniles, were collected from 12 estuaries and associated habitats in the warm temperate region of South Africa between July 1998 and December 2000. This study served to provide new information and expand on existing knowledge of early stage fish assemblages associated with various types of Eastern Cape estuaries. A total of 65 536 predominantly postflexion fish larvae were collected. Together with early juveniles, taxa comprised 72 species from 25 teleost fish families. Surf zones associated with two intermittently open estuaries showed that estuary-dependent marine species predominated in this zone. Early stage fishes responded positively during natural estuary opening events and concentrated along the estuary outflow plume, suggesting that cueing from estuary and/or river water may be taking place. A habitat study in the Swartkops Estuary, using light traps, showed that newly recruited larval fishes concentrated along the margins of the estuary and unlike their older juvenile counterparts, were poorly represented in eelgrass beds. A multi-estuary comparison, including seven permanently open and five intermittently open estuaries, indicated that early stage fish assemblages were more diverse than indicated by past investigations. Early stage fishes were also shown to concentrate in the mesohaline regions of these estuaries. Studies of estuaries with altered freshwater flow regimes were also included in the research. A regulated release of dam water in the euhaline Kromme Estuary failed to induce a cueing response from estuary-dependent marine fish larvae. This project showed that large amounts of freshwater are required to reverse the negative effects of river impoundments. The release study did show that estuary-resident fishes were sensitive to small natural pulses of freshwater and responded by spawning. However, excessive river supply through an inter-basin water transfer scheme was shown to have a flushing effect on the larvae and early juveniles of the estuary-resident Gilchristella aestuaria in the upper reaches of the Great Fish Estuary. This effect was evident in comparisons with the freshwater starved Kariega Estuary where concentrations of G. aestuaria, a species usually more abundant in freshwater rich estuaries, were considerably higher. This finding suggests that freshwater minima and maxima be considered when assessing and managing estuarine systems.
- Full Text:
- Date Issued: 2002
- Authors: Strydom, Nadine Amelia
- Date: 2002
- Subjects: Estuarine fishes -- South Africa Fishes -- Infancy -- South Africa Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5262 , http://hdl.handle.net/10962/d1005106
- Description: Early stage fishes, namely larvae and early juveniles, were collected from 12 estuaries and associated habitats in the warm temperate region of South Africa between July 1998 and December 2000. This study served to provide new information and expand on existing knowledge of early stage fish assemblages associated with various types of Eastern Cape estuaries. A total of 65 536 predominantly postflexion fish larvae were collected. Together with early juveniles, taxa comprised 72 species from 25 teleost fish families. Surf zones associated with two intermittently open estuaries showed that estuary-dependent marine species predominated in this zone. Early stage fishes responded positively during natural estuary opening events and concentrated along the estuary outflow plume, suggesting that cueing from estuary and/or river water may be taking place. A habitat study in the Swartkops Estuary, using light traps, showed that newly recruited larval fishes concentrated along the margins of the estuary and unlike their older juvenile counterparts, were poorly represented in eelgrass beds. A multi-estuary comparison, including seven permanently open and five intermittently open estuaries, indicated that early stage fish assemblages were more diverse than indicated by past investigations. Early stage fishes were also shown to concentrate in the mesohaline regions of these estuaries. Studies of estuaries with altered freshwater flow regimes were also included in the research. A regulated release of dam water in the euhaline Kromme Estuary failed to induce a cueing response from estuary-dependent marine fish larvae. This project showed that large amounts of freshwater are required to reverse the negative effects of river impoundments. The release study did show that estuary-resident fishes were sensitive to small natural pulses of freshwater and responded by spawning. However, excessive river supply through an inter-basin water transfer scheme was shown to have a flushing effect on the larvae and early juveniles of the estuary-resident Gilchristella aestuaria in the upper reaches of the Great Fish Estuary. This effect was evident in comparisons with the freshwater starved Kariega Estuary where concentrations of G. aestuaria, a species usually more abundant in freshwater rich estuaries, were considerably higher. This finding suggests that freshwater minima and maxima be considered when assessing and managing estuarine systems.
- Full Text:
- Date Issued: 2002
Modelling the distribution and abundance of several demersal fish species on the Agulhas Bank, South Africa
- Authors: Sampson, Mark Robert
- Date: 2002
- Subjects: Fishes -- South Africa -- Geographical distribution , Fishes -- South Africa -- Geographical distribution -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5343 , http://hdl.handle.net/10962/d1006207 , Fishes -- South Africa -- Geographical distribution , Fishes -- South Africa -- Geographical distribution -- Mathematical models
- Description: The Agulhas Bank supports a speciose fish community, many of which are commercially important. Despite substantial research being conducted on aspects of their biology spatial aspects of their distribution and abundance in relation to environment parameters has been ignored. This study, therefore, addressed aspects related to the distribution and abundance of representative species on the Agulhas Bank within a Geographic Information System (GIS). Four candidate species were chosen due to their importance either in numbers or unit mass to the South African demersal trawl fishery. The species also shared morphological and taxonomic similarities. The candidate species chosen were the two Cape hake species, shallow-water hake Meluccius capensis, and deep-water hake Merluccius paradoxus, and the two pleuronectiform species being Agulhas sole Austroglossus pectoralis and redspotted tonguesole Cynoglossus zanzibarensis. The use of a GIS was appropriate and allowed for hidden spatial patterns be exposed and illustrated visually, while also facilitating the quantification of the relationships between distribution/abundance and certain environmental predictors using statistical methods The Department of Marine and Coastal Management, Cape Town, supplied biological data in the form of length frequency and biomass information from spring (AprillMay) and autumn (September/October) cruises conducted between 1986 and 1993 on the R. V. Africana. The Council for National Geoscience, Cape Town, supplied sediment data for the entire southern African coastline. Initial exploratory data analysis highlighted potential relationships between environmental variables and abundance for each specie's life-history stanzas. Variations in spatial distribution were found to be significantly different between each life-history stanzas within species. Fish density as a function of the additive effects of the various environmental parameters, including temperature, depth and sediment type, was assessed using a Poisson Generalized Additive Model (GAM), while distribution was analysed with a logistic GAM. A predictive logistic model was then created, taking into consideration the importance of the predictor variables for each species, allowing for predictive estimates to be made for each species by inputting environmental information within the study area. The importance of certain environmental variables influencing distribution and abundance were noted. General patterns indicated that sediment was the most important to both the distribution and abundance of the two pleuronectiform species and juvenile life-history stanzas, while the adult gadoids' distribution and abundance appeared to be depth dependent.
- Full Text:
- Date Issued: 2002
- Authors: Sampson, Mark Robert
- Date: 2002
- Subjects: Fishes -- South Africa -- Geographical distribution , Fishes -- South Africa -- Geographical distribution -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5343 , http://hdl.handle.net/10962/d1006207 , Fishes -- South Africa -- Geographical distribution , Fishes -- South Africa -- Geographical distribution -- Mathematical models
- Description: The Agulhas Bank supports a speciose fish community, many of which are commercially important. Despite substantial research being conducted on aspects of their biology spatial aspects of their distribution and abundance in relation to environment parameters has been ignored. This study, therefore, addressed aspects related to the distribution and abundance of representative species on the Agulhas Bank within a Geographic Information System (GIS). Four candidate species were chosen due to their importance either in numbers or unit mass to the South African demersal trawl fishery. The species also shared morphological and taxonomic similarities. The candidate species chosen were the two Cape hake species, shallow-water hake Meluccius capensis, and deep-water hake Merluccius paradoxus, and the two pleuronectiform species being Agulhas sole Austroglossus pectoralis and redspotted tonguesole Cynoglossus zanzibarensis. The use of a GIS was appropriate and allowed for hidden spatial patterns be exposed and illustrated visually, while also facilitating the quantification of the relationships between distribution/abundance and certain environmental predictors using statistical methods The Department of Marine and Coastal Management, Cape Town, supplied biological data in the form of length frequency and biomass information from spring (AprillMay) and autumn (September/October) cruises conducted between 1986 and 1993 on the R. V. Africana. The Council for National Geoscience, Cape Town, supplied sediment data for the entire southern African coastline. Initial exploratory data analysis highlighted potential relationships between environmental variables and abundance for each specie's life-history stanzas. Variations in spatial distribution were found to be significantly different between each life-history stanzas within species. Fish density as a function of the additive effects of the various environmental parameters, including temperature, depth and sediment type, was assessed using a Poisson Generalized Additive Model (GAM), while distribution was analysed with a logistic GAM. A predictive logistic model was then created, taking into consideration the importance of the predictor variables for each species, allowing for predictive estimates to be made for each species by inputting environmental information within the study area. The importance of certain environmental variables influencing distribution and abundance were noted. General patterns indicated that sediment was the most important to both the distribution and abundance of the two pleuronectiform species and juvenile life-history stanzas, while the adult gadoids' distribution and abundance appeared to be depth dependent.
- Full Text:
- Date Issued: 2002
Nutrient digestibility in South African abalone (Haliotis Midae L.)
- Authors: Sales, James
- Date: 2002
- Subjects: Abalones -- Digestion Abalones -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5305 , http://hdl.handle.net/10962/d1005150
- Description: The evaluation of potential alternative protein sources for the formulation of least-cost optimal diets to satisfy the nutrient requirements of South African abalone (Haliotis midae) has been hampered by the absence of a suitable, practical, replicable and reliable digestibility technique. A suitable lowcost faeces collection technique was developed in this study to obtain suitable quantities of excreta for analysis from this species. Acid-insoluble ash was identified as a reliable, replicable and safe internal marker in comparison to chromic oxide and crude fibre for use in nutrient digestibility studies with H. midae. This was validated by the consistency and repeatability of the results and by comparison to total collection of faeces. The traditional substitution method used in digestibility studies with fish to evaluate protein digestibility of feed ingredients was found to be unsuitable for H. midae. Apparent protein digestibility values exceeding 100 % derived through this method could be attributed to associative effects between feed ingredients, differential diet and faecal nutrient leaching, and mathematical artifacts in calculations when using substitution versus single protein diets. An ingredient particle size of less than 450 μm in comparison to particle size classes of above 450 μm was shown to enhance nutrient (dry matter, organic matter, protein, fat) digestibility and minimise dry matter leaching from diets. The dietary inclusion level of both pre-gelatinised maize starch and a-cellulose did not influence (P > 0.05) apparent nutrient (protein, fat, fiber, starch) digestibility. Using the above digestibility protocol amino acid availability of all plants ingredients currently used in the South African animal industry was evaluated for H. midae. Soybean meal (96.86 %) and lupins (96.51 %) presented the highest apparent mean amino acid availability of all plant protein ingredients evaluated with H. midae. Canola meal (94.21 %), faba beans (92.87 %) sunflower meal (92.77 %), peanut meal (87.39 %) and cottonseed meal (85.15 %) presented higher apparent mean amino acid availability values than fish meal (82.75 %). Apparent protein digestibility was highly correlated (r = 0.99) with mean apparent amino acid availability, while true amino acid availability was 1.88 % units higher than apparent amino acid availability for all ingredients tested. Predicted apparent protein digestibility in compound diets was within 1.1-6.5 % of determined values. Calcium phosphate mono dibasic presented the lowest (P < 0.05) dietary phosphorus leaching (51.51 % maximum) and highest apparent phosphorus digestibility (66.27 %) in comparison to other inorganic phosphorus sources. Based on the method of direct experimentation to determine the optimal dietary protein level using graded levels of dietary protein 28.1-35.9 % dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae. This study provides a scientifically sound research tool including a faecal collection technique, suitable marker and assay technique that could be use in further studies to improve least-cost diet formulation for H. midae. Future nutritional studies in H. midae should primarily concentrate on reducing dietary nutrient leaching and improving the intake of nutrients in order to properly evaluate responses of this species to different dietary regimes.
- Full Text:
- Date Issued: 2002
- Authors: Sales, James
- Date: 2002
- Subjects: Abalones -- Digestion Abalones -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5305 , http://hdl.handle.net/10962/d1005150
- Description: The evaluation of potential alternative protein sources for the formulation of least-cost optimal diets to satisfy the nutrient requirements of South African abalone (Haliotis midae) has been hampered by the absence of a suitable, practical, replicable and reliable digestibility technique. A suitable lowcost faeces collection technique was developed in this study to obtain suitable quantities of excreta for analysis from this species. Acid-insoluble ash was identified as a reliable, replicable and safe internal marker in comparison to chromic oxide and crude fibre for use in nutrient digestibility studies with H. midae. This was validated by the consistency and repeatability of the results and by comparison to total collection of faeces. The traditional substitution method used in digestibility studies with fish to evaluate protein digestibility of feed ingredients was found to be unsuitable for H. midae. Apparent protein digestibility values exceeding 100 % derived through this method could be attributed to associative effects between feed ingredients, differential diet and faecal nutrient leaching, and mathematical artifacts in calculations when using substitution versus single protein diets. An ingredient particle size of less than 450 μm in comparison to particle size classes of above 450 μm was shown to enhance nutrient (dry matter, organic matter, protein, fat) digestibility and minimise dry matter leaching from diets. The dietary inclusion level of both pre-gelatinised maize starch and a-cellulose did not influence (P > 0.05) apparent nutrient (protein, fat, fiber, starch) digestibility. Using the above digestibility protocol amino acid availability of all plants ingredients currently used in the South African animal industry was evaluated for H. midae. Soybean meal (96.86 %) and lupins (96.51 %) presented the highest apparent mean amino acid availability of all plant protein ingredients evaluated with H. midae. Canola meal (94.21 %), faba beans (92.87 %) sunflower meal (92.77 %), peanut meal (87.39 %) and cottonseed meal (85.15 %) presented higher apparent mean amino acid availability values than fish meal (82.75 %). Apparent protein digestibility was highly correlated (r = 0.99) with mean apparent amino acid availability, while true amino acid availability was 1.88 % units higher than apparent amino acid availability for all ingredients tested. Predicted apparent protein digestibility in compound diets was within 1.1-6.5 % of determined values. Calcium phosphate mono dibasic presented the lowest (P < 0.05) dietary phosphorus leaching (51.51 % maximum) and highest apparent phosphorus digestibility (66.27 %) in comparison to other inorganic phosphorus sources. Based on the method of direct experimentation to determine the optimal dietary protein level using graded levels of dietary protein 28.1-35.9 % dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae. This study provides a scientifically sound research tool including a faecal collection technique, suitable marker and assay technique that could be use in further studies to improve least-cost diet formulation for H. midae. Future nutritional studies in H. midae should primarily concentrate on reducing dietary nutrient leaching and improving the intake of nutrients in order to properly evaluate responses of this species to different dietary regimes.
- Full Text:
- Date Issued: 2002
A taxonomic revision of the shallow-water species of the genera Lethrinops, Tramitichromis and Taeniolethrinops (Teleostei, Cichlidae) from Lake Malawi/Nyasa/Niassa (East Africa)
- Authors: Ngatunga, Benjamin Peter
- Date: 2001
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5347 , http://hdl.handle.net/10962/d1007443
- Description: In order for the SADC/GEF Lake Malawi/Nyasa Biodiversity Conservation Project to draw out sound strategic management and conservation recommendations to the riparian countries of Malawi, Mozambique and Tanzania, the need and urgency for revising the taxonomy of some of the scientifically and economically important fish groups was accorded high priority. This study is a contribution towards achieving those goals. It is a taxonomic revision of the shallow-water species of the genera Taenioiethrinops, Tramitichromis and Lethrinops. These three genera are grouped as Lethrinops 'sensu lato' in this thesis, corresponding to the definition of Lethrinops prior to the revision by Eccles & Trewavas (1989). All members have a characteristic dentition: the outer teeth in the lower jaw curve inwards posteriorly ending just behind the inner row(s), rather than continuing backwards as a single series, as in most other Malawian haplochromines. The decision to consider shallow-water Lethrinops 'sensu lato' separately from the deepwater ones was not arbitrary, but rather based on available ecological and morphological evidence. Unanticipatedly, on the course of this study, evidence from molecular genetics has helped to strengthen the distinction. Economically, Lethrinops is important for human food and for the aquarium trade. Lethrinops are precocial fish producing very few young at a time and are consequently unlikely to recover quickly from heavy fishing pressure. To evolutionary biologists, Lethrinops 'sensu lato' is challenging because until now most theories about the evolution of Lake Malawi cichlids have not taken the sand-dwelling fishes fully into consideration. A better knowledge of the distribution patterns of these cichlids, of which Lethrinops are the major representatives, can help in explaining the underlying mechanisms of speciation in sand-dwelling cichlids. Lethrinops 'sensu lato' is taxonomically one of the most complex groups of Lake MalawilNyasa haplochromines. The species are closely related and very difficult to differentiate, and the taxonomy is confused and in urgent need of revision. This is more important since taxonomy plays an important role in most of the key criteria of conservation.The principal objective of this study was to carry out a taxonomic revision of this group and to provide a key to the identification of the species. Further objectives include the mapping of their distribution and analysing their phylogenetic relationships. Large samples were collected (by trawling, gill netting, beach seining and purchased from local fishermen) from depths less than 20m and from numerous well-defined localities all around the lake. Seventeen type specimens of the 21 described species of the shallow-water Lethrinops 'sensu lato' were examined and compared with this recently collected material. The data of about 500 fish specimens were subjected to principal component analyses (PCA). To further evaluate morphological differences between taxa of comparable size, non- parametric, distribution-free Mann-Whitney U-tests were used. Within the shallow-water Lethrinops 'sensu lato' three genera are recognized which can be separated by characters such as head shape, pharyngeal morphology and dentition, number and shape of gill-rakers, number of the pectoral fin rays and melanin pattern. So far in this study, 28 taxa have been recognized. The overlapping measurements and meristics compound the difficulty inherent in the identification and classification of members of the three genera. The genera Tramitichromis and Taeniolethrinops are typically shallow- water taxa. Within the genus Taeniolethrinops four described species, (T. cyrtonotus, T.forcicauda, T. laticeps and T. praeorbitalis) were distinguished. Within the genus Tramitichromis nine species were distinguished, five of which are described (T. brevis, T. intermedius, T. lituris, T. trilineata and T. variabilis); four represent undescribed species and are given a working name (T. sp. 'brevis 2', T. sp. 'maculae', T. sp. 'pharyngeals' and T. sp. 'variabilis deep'). For convenience, the shallow water Lethrinops 'sensu stricto' were divided into three natural groups, according to shared morphological features. • The first group is the lethrinus group, including three species (L. lunaris, L. leptodon and L. lethrinus) with relatively lolong snouts and remnants of the horizontal stripes. • Another group included eight taxa (L. microstoma, L. macrophthalmus, L. macrochir, L. auritus, L. parvidens, L. sp. 'parvidens deep', L. 'black dorsal auritus', L. sp. 'domira blotch' and L. sp. 'turneri') with a relatively short snout and a small mouth set low on the profile. Within this group, special attention has been paid to the confusion involving L. auritus and a new species to be described soon, L. sp. 'turneri' . • The last group of Lethrinops 'sensu stricto' is ill defmed and has an intermediate snout and with a lesser round head. Within this group L. oculatus, which was described on the basis of a single specimen, is synonymised with L. marginatus. The other valid species of this group are Lethrinops albus and L.furcifer. Nearly all species seem to have a lake-wide distribution. All are associated with sandy substrata where they feed mainly on insect larvae and ostracods. Mitochondrial DNA sequence data indicate that Lethrinops 'sensu lato' as currently defmed is not monophyletic but is paraphyletic or more probably polyphyletic. It is further suggested that the typical Lethrinops dentition provides no particular strong evidence for affimity among shallow-water Lethrinops s.s., Tramitichromis and Taeniolethrinops. The need for management and conservation of this scientifically exciting group of fishes has been pointed out.
- Full Text:
- Date Issued: 2001
- Authors: Ngatunga, Benjamin Peter
- Date: 2001
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5347 , http://hdl.handle.net/10962/d1007443
- Description: In order for the SADC/GEF Lake Malawi/Nyasa Biodiversity Conservation Project to draw out sound strategic management and conservation recommendations to the riparian countries of Malawi, Mozambique and Tanzania, the need and urgency for revising the taxonomy of some of the scientifically and economically important fish groups was accorded high priority. This study is a contribution towards achieving those goals. It is a taxonomic revision of the shallow-water species of the genera Taenioiethrinops, Tramitichromis and Lethrinops. These three genera are grouped as Lethrinops 'sensu lato' in this thesis, corresponding to the definition of Lethrinops prior to the revision by Eccles & Trewavas (1989). All members have a characteristic dentition: the outer teeth in the lower jaw curve inwards posteriorly ending just behind the inner row(s), rather than continuing backwards as a single series, as in most other Malawian haplochromines. The decision to consider shallow-water Lethrinops 'sensu lato' separately from the deepwater ones was not arbitrary, but rather based on available ecological and morphological evidence. Unanticipatedly, on the course of this study, evidence from molecular genetics has helped to strengthen the distinction. Economically, Lethrinops is important for human food and for the aquarium trade. Lethrinops are precocial fish producing very few young at a time and are consequently unlikely to recover quickly from heavy fishing pressure. To evolutionary biologists, Lethrinops 'sensu lato' is challenging because until now most theories about the evolution of Lake Malawi cichlids have not taken the sand-dwelling fishes fully into consideration. A better knowledge of the distribution patterns of these cichlids, of which Lethrinops are the major representatives, can help in explaining the underlying mechanisms of speciation in sand-dwelling cichlids. Lethrinops 'sensu lato' is taxonomically one of the most complex groups of Lake MalawilNyasa haplochromines. The species are closely related and very difficult to differentiate, and the taxonomy is confused and in urgent need of revision. This is more important since taxonomy plays an important role in most of the key criteria of conservation.The principal objective of this study was to carry out a taxonomic revision of this group and to provide a key to the identification of the species. Further objectives include the mapping of their distribution and analysing their phylogenetic relationships. Large samples were collected (by trawling, gill netting, beach seining and purchased from local fishermen) from depths less than 20m and from numerous well-defined localities all around the lake. Seventeen type specimens of the 21 described species of the shallow-water Lethrinops 'sensu lato' were examined and compared with this recently collected material. The data of about 500 fish specimens were subjected to principal component analyses (PCA). To further evaluate morphological differences between taxa of comparable size, non- parametric, distribution-free Mann-Whitney U-tests were used. Within the shallow-water Lethrinops 'sensu lato' three genera are recognized which can be separated by characters such as head shape, pharyngeal morphology and dentition, number and shape of gill-rakers, number of the pectoral fin rays and melanin pattern. So far in this study, 28 taxa have been recognized. The overlapping measurements and meristics compound the difficulty inherent in the identification and classification of members of the three genera. The genera Tramitichromis and Taeniolethrinops are typically shallow- water taxa. Within the genus Taeniolethrinops four described species, (T. cyrtonotus, T.forcicauda, T. laticeps and T. praeorbitalis) were distinguished. Within the genus Tramitichromis nine species were distinguished, five of which are described (T. brevis, T. intermedius, T. lituris, T. trilineata and T. variabilis); four represent undescribed species and are given a working name (T. sp. 'brevis 2', T. sp. 'maculae', T. sp. 'pharyngeals' and T. sp. 'variabilis deep'). For convenience, the shallow water Lethrinops 'sensu stricto' were divided into three natural groups, according to shared morphological features. • The first group is the lethrinus group, including three species (L. lunaris, L. leptodon and L. lethrinus) with relatively lolong snouts and remnants of the horizontal stripes. • Another group included eight taxa (L. microstoma, L. macrophthalmus, L. macrochir, L. auritus, L. parvidens, L. sp. 'parvidens deep', L. 'black dorsal auritus', L. sp. 'domira blotch' and L. sp. 'turneri') with a relatively short snout and a small mouth set low on the profile. Within this group, special attention has been paid to the confusion involving L. auritus and a new species to be described soon, L. sp. 'turneri' . • The last group of Lethrinops 'sensu stricto' is ill defmed and has an intermediate snout and with a lesser round head. Within this group L. oculatus, which was described on the basis of a single specimen, is synonymised with L. marginatus. The other valid species of this group are Lethrinops albus and L.furcifer. Nearly all species seem to have a lake-wide distribution. All are associated with sandy substrata where they feed mainly on insect larvae and ostracods. Mitochondrial DNA sequence data indicate that Lethrinops 'sensu lato' as currently defmed is not monophyletic but is paraphyletic or more probably polyphyletic. It is further suggested that the typical Lethrinops dentition provides no particular strong evidence for affimity among shallow-water Lethrinops s.s., Tramitichromis and Taeniolethrinops. The need for management and conservation of this scientifically exciting group of fishes has been pointed out.
- Full Text:
- Date Issued: 2001