The biology and systematics of South African pipefishes of the genus Syngnathus
- Authors: Mwale, Monica
- Date: 2007
- Subjects: Pipefishes -- South Africa Syngnathus -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5237 , http://hdl.handle.net/10962/d1005080
- Description: Syngnathus the most speciose genus in the family Syngnathidae is widely in the Atlantic and Eastern Pacific oceans. However, it is poorly represented in the Indian Ocean with the only two species, Syngnathus temminckii and S. watermeyeri occurring in Southern African estuaries and coastal areas. Syngnathus temminckii the most common South African pipefish has been synonymised with S. acus, as the morphological and genetic divergence between these two populations has not been documented. There is also uncertainty in the taxonomic status of S. watermeyeri, an endemic estuarine pipefish that is restricted to two Eastern Cape estuaries. The purpose of this study was therefore to compare biological, morphological and genetic variation of South African Syngnathus species among different populations/locations, and with European populations of S. acus. Sixteen meristic and ten morphometric characteristics were quantified from specimens obtained from field as well as various international natural history museum collections. Univariate (ANOVA) and multivariate (principal component analysis and discriminant analyses) analyses were used to assess morphological differences among the species. Morphometric variables were adjusted as ratios of the standard length and using an allometric procedure. ANCOVA analysis indicated significant differences between S. acus and S. temminckii for the relationships of the standard length (SL) and all morphological characters. There was no significant correlation between SL and snout length, snout depth, inter-orbital width and trunk depth for S. watermeyeri. The analyses provided evidence for distinct populations of S. acus, S. temminckii and S. watermeyeri although morphological character differentiation was greater between S. watermeyeri and the other two larger species. Although, significant differences were observed for meristic characters, pairwise comparisons did not reflect a clear pattern of variability. Most of the measured morphological characters contributed more than 70% to the morphological variation between the populations. Plot of the canonical scores for the variables resulted in the specimens clustering according to species groups and locations of S. temminckii. Sequences of 750 base pairs of the mitochondrial cytochrome gene from 11 localities were compared with published sequences of other species of Syngnathus. Phylogenetic analysis was performed using parsimony, maximum likelihood (ML) and Bayesian inference (BI). The South African species were revealed to be sister-taxa with about 6 % divergence, while S. temminckii and S. acus had about 11% sequence divergence. 20 haplotypes among 46 total specimens from the three species. Gene flow was estimated at approximately 3 migrants per generation between the two South African populations and about 1 per generation between S. temminckii and S. acus. Such strong stock structuring among presumably recently established post-Pliocene (< 2 Million years ago) populations suggests that these species are reproductively isolated. Morphological and genetic variation observed in this study combined with current knowledge of life history attributes of the South African pipefishes indicate that conservative management decisions are necessary until the patterns and extent of differentiation among populations species-wide can be investigated further. It is thus being proposed that the name of the South African population of S. acus be changed to Syngnathus temminckii (Kaup, 1856).
- Full Text:
- Date Issued: 2007
The biology of austroglanis gilli and austroglanis barnardi (siluriformes : austroglanididae) in the Olifants River system, South Africa
- Authors: Mthombeni, Vusi Gedla
- Date: 2010
- Subjects: Catfishes -- South Africa -- Olifants River , Fishes -- South Africa -- Olifants River -- Growth , Freshwater fishes -- Effect of pesticides on -- South Africa -- Olifants River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5370 , http://hdl.handle.net/10962/d1015222
- Description: Austroglanis gilli and A. barnardi are endemic to the Clanwilliam-Olifants System in the Western Cape, South Africa. The populations of each of these species are considered to be threatened by various anthropogenic activities, which include inappropriate agricultural practice and impacts of alien invasive fish species. The purpose of this thesis was to assess the life-history of these two endangered species in order to contribute to understanding their biology. Such information is vital for the development of strategies for their conservation. Marginal zone and marginal increment analyses from sectioned lapilliar otoliths of both A. gilli and A. barnardi showed a unimodal peak, suggesting a single annulus formation. The oldest specimens of A. gilli and A. barnardi were 12+ and 14+ years, respectively. The growth of A. gilli and A. barnardi was relatively slow and was best described by the von Bertalanffy growth curve as: L, = 131.56(1 - exp(- 0.27(t - 1.18 ))) for male and L, = 113.86(1 - exp(- 0.43(1- 0.74))) for female A. gilli from the Rondegat River. In the Noordhoeks River, growth was L, = 99.67(1 - exp(- 0.53(t - 0.35))) for male and L, = 96.60(1 - exp(- 0.64(t - 0.11 ))) for female A. gilli, and L, =71.02(1-exp(-0.26(1-3.07))) and L, = 69.50(1-exp(-0.36(1 - 1.88))) for male and female A. barnardi, respectively. The average natural mortality for the combined sexes was estimated using catch curve analysis at 0.37 ± 0.12 per year for A. gilli from the Rondegat River, and at 0.71 ± 0.05 and 0.39 ± 0.04 per year for A. gilli and A. barnardi from the Noordhoeks River, respectively. For A. gilli in the Rondegat River, the first maturity was estimated at 3.3 years (97.3 mm SL) for males and 3.1 years (94.3 mm SL) for females. In the Noordhoeks River, the first maturity for A. gilli was estimated at 2.0 years (71.9 mm SL) for males and 1.7 (66.4 mm SL) for females, and for A. barnardi at 2.0 (55.0 nun SL) for males and 2.9 years (58.9 mm SL) for females. Maturity corresponded closely to the asymptotic sizes from the von Bertalanffy curves, suggesting a shift in energy use from somatic growth to gonad development. Macroscopic assessment of the state of gonads, the Ganado-somatic index and histological examinations revealed that both A. gilli and A. barnardi have a single spawning season. The presence of oocytes in different stages of development in each of the ovaries of mature females collected between November and January suggested asynchronous, iteroperous serial spawning. The resorption of yolk was observed from ovaries collected between February and March and no vitellogenic oocyte was visible from ovaries collected between April and August. A similar trend was observed for males, with spermatozoa filling the lumen between November and January and some residual spermatozoa being present in the lumens soon after the breeding season. Spermatocytes and spermatids were dominant in the testes until October. An Index of Relative Importance revealed that A. gilli feeds predominantly on the benthic macroinvertebrate larvae of Ephemeroptera (particularly Baetidae), Diptera (particularly Chironomidae and Simuliidae) and Trichoptera. Austroglanis barnardi feeds predominantly on dipteran larvae (particularly Chironornidae and Simuliidae). Chi square contingency tables showed a significant difference in the dominant prey items of A. gilli and A. barnardi in the Noordhoeks River (X₂= 53.79, d.f. = 4, p > 0.001) and A. gilli between Rondegat and Noordhoeks rivers (x₂ = 34.74, d.f. = 4, p > 0.001). The Spearman's rank correlation test showed no shifts in the diet of A. barnardi from Noordhoeks River and A. gilli from Rondegat River with a change in size and season (p>O.OS). However, there was a shift in the diet of A. gilli from the Noordhoeks River which could suggest a distinct patchiness of benthic macroinvertebrates between the riffle feeding areas used by juveniles and other biotopes used by adults. The occurrence, in stomach contents, of other prey items from a wide variety of taxa and the presence of allochthonous material from the terrestrial environment could suggest an opportunistic feeding guild for both Austroglanis species. The life-history traits of A. gilli and A. barnardi, which are charaterized by slow growth, long life span and low relative fecundity, indicate that both species are relatively precocial and K-selected. The population of a precocial species is relatively stable and if population numbers were to be greatly reduced, they would require a long time to rebuild. An urgent conservation intervention is therefore recommended for Austroglanis spp. so as to maintain the diversity of populations within these species. The creation of protected river reserves and raising public conservation awareness may minimise activities that result in altered river hydrology and the destruction of complex benthic habitats.
- Full Text:
- Date Issued: 2010
The biology of commercially important fish species and a preliminary assessment of the fisheries potential of Katse Dam, Lesotho
- Authors: Nthimo, Mokitinyane Francis
- Date: 2000
- Subjects: Fishes -- Lesotho -- Katse dam , Fishes -- Physiology , Rainbow trout , Barbus aeneus , Labeo , Katse dam (Lesotho) , Fisheries -- Lesotho -- Katse dam , Fishery management -- Lesotho
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5238 , http://hdl.handle.net/10962/d1005081 , Fishes -- Lesotho -- Katse dam , Fishes -- Physiology , Rainbow trout , Barbus aeneus , Labeo , Katse dam (Lesotho) , Fisheries -- Lesotho -- Katse dam , Fishery management -- Lesotho
- Description: The construction of the Katse dam was completed in 1996. The dam started filling in 1995 and reached full capacity in early 1998. It forms part of Phase 1A of the Lesotho Highlands Water Project (LHWP). The main aim of the project is to provide revenue to Lesotho, by transferring water from the catchment of the Senqu (Orange) River in Lesotho to South Africa’s major industrial and population centres. During the implementation of the project, an estimated 130 people were displaced. However, the most serious impact has been the loss of the traditional way of life in the form of arable and grazing land as a consequence of inundation. One of the obligations of the project is to ensure that the standard of living of those affected by the project is not impaired. The Lesotho Highlands Development Authority identified a number of rural development projects, which included fisheries development. This study is an integral part of fisheries development in Lesotho. The aim of this study was to gain an understanding of the biology and the demographics of the fish species in the lake. This information would serve as the basis for the development of a management plan for the sustainable utilisation of the fisheries resources. To achieve this aim, the following specific objectives were addressed: 1. Investigation of the biology of the three principal species. 2. Description of the key population parameters (growth, mortality & recruitment). 3. Investigation of the distribution and relative abundance of the three species. The three principal species in the Katse dam are rainbow trout, Oncorhynchus mykiss, and the two cyprinids, Barbus aeneus and Labeo capensis. Sectioned otoliths were used to age O. mykiss while both otoliths and scales were used to age B. aeneus and L. capensis. Marginal zone analysis revealed that slow growth was experienced in winter for the three species. The maximum-recorded age for both B. aeneus and L. capensis was 12 years while O. mykiss reached 4 years. There was no significant difference in growth rates of the different sexes and growth was best described by the 3 parameter Von-Bertalanfy growth model as Lt = 603[1-e⁻°·¹⁵⁽t ⁺ °·°³⁾] for B. aeneus, Lt = 526[1-e⁻°·²¹⁽t ⁺ °·⁹⁾] for O. mykiss and Lt = 521[1-e⁻°·¹⁷⁽t ⁺ °·²¹⁾] for L.capensis. Male and female O. mykiss attained 50% sexual maturity (Lm₅₀) at 235 and 275mm FL, respectively. There was no difference in Lm₅₀ for male and female B. aeneus and L. capensis. B. aeneus reached sexual maturity at 285mm FL while L. capensis reached sexual maturity at 244mm. Both cyprinid species spawned in summer (November to January) while O. mykiss spawned in winter (May to August). The mean total mortality rate (Z) estimated from catch curves and Butterworth et al (1989) equation was 0.72 yr⁻¹ for B. aeneus, 0.62 yr⁻¹ for L. capensis and 1.32 yr⁻¹ for O. mykiss. The estimate of natural mortality was 0.41 yr⁻¹ for both B. aeneus and L. capensis and 0.81yr⁻¹ for O. mykiss.
- Full Text:
- Date Issued: 2000
The biology of four haplochromine species of Lake Kivu (Zaïre) with evolutionary implications
- Authors: Losseau-Hoebeke, Michèle
- Date: 1992
- Subjects: Cichlids -- Research -- Kivu, Lake (Congo and Rwanda) , Cichlids -- Ecology -- Research , Cichlids -- Breeding -- Research , Cichlids -- Evolution -- Research , Haplochromis -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5239 , http://hdl.handle.net/10962/d1005082 , Cichlids -- Research -- Kivu, Lake (Congo and Rwanda) , Cichlids -- Ecology -- Research , Cichlids -- Breeding -- Research , Cichlids -- Evolution -- Research , Haplochromis -- Research
- Description: Four species were selected within the littoral of Tshegera Island, and include H. astatodon, H. olivaceus, H. crebridens and H. paucidens. These species, identified on basis of the SMRS, express their individuality most strongly with respect to dentition, breeding colours, normal habitat and preferred breeding territory. All four species are maternal mouthbrooders. This reproductive strategy is characterized by complete division of labour and polygamy. Breeding males compete for optimal territories and ready to spawn females. They are characterized by fast growth, large size and overall low condition factor. Females invest in few but large yolked ova and go through a fasting period while incubating the eggs. Females are generally characterized by slower growth, smaller size and higher condition factor when compared to males. In females the energy turnover during gonadal development and subsequent mouthbrooding is high, but the energy expenditure low. Mean fecundity varies between 25 and 36 eggs per brood and mean egg size between 2.6 and 2.7 rnrn. The right ovary, although small, is functional. Breeding of variable intensity goes on throughout the year. The main dry season corresponds to synchronized breeding. During the other months of the year species breed asynchronously. Both types of breeding are related to food availability for adults and offspring. The major breeding peak which starts in July coincides to improved body condition in both sexes. In similarity with the East African flocks, the Lake Kivu haplochromines display subdivision within the major trophic groups and invasion of the major lacustrine habitats. They are nevertheless morphologically and ecologically generalized. They tend to be plesiomorphic with low diversification within each trophic group, have a lake wide distribution (eurytopic) and incline to be altricial within their specialized reproductive guild. The evolutionary status of the Lake Kivu haplochromines may be explained by survival of members of an ancestral fauna in an isolated bay during the Recent volcanic events which destroyed life in the Main Basin. The Lake Kivu flock, therefore, is a relict and is believed not to have evolved within the confines of the present-day lake.
- Full Text:
- Date Issued: 1992
The biology of two important by-catch skate species on the Agulhas Bank, South Africa
- Authors: Walmsley, Sarah Ann
- Date: 1997
- Subjects: Skates (Fishes) -- South Africa -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5240 , http://hdl.handle.net/10962/d1005083 , Skates (Fishes) -- South Africa -- Physiology
- Description: Members of the family Rajidae are common components of the demersal trawl fishery, contributing around 1% to the total catch. However, apart from a single species all South African rajids are currently discarded. With demands for new protein sources ever-increasing, it is possible that currently underutilised species, such as the skates will be utilized to a greater extent. Raja wallacei and R.pullopunctata are common trawler by-catch species, ranging along most of the South African coast. The current study allred to further knowledge on the population biology of both species through age and growth, reproductive and feeding studies. The study also allred to assess whether any of the South African skate species show the potential for utilization as a food source. Band counts of vertebral centra were used to determine growth parameters and generate growth curves for males and females of both species. Growth was significantly different between the sexes. In both cases, females grew slower than males but reached a greater asymptotic disc width. As with other elasmobranchs, R.wallacei and R.pullopunctata are long-lived and slow growing. As with all other skates, the study species are oviparous laying large, yolked eggs in tough, leathery cases on the sea bed. The onset of maturity occurs at a large size (approximately 400mm disc width (10-11 years of age) for R.wallacei and 600mm disc width (12-13 years of age) for Rpullopunctata) and is very rapid. The oldest R.wallacei and R.pullopunctata observed were 16 and 18 years of age, respectively. No distinct breeding season was determined and no nursery areas were observed. A large proportion of individuals, especially R.pullopunctata was immature. Both species fed primarily on crustaceans and teleosts with an ontogenetic shift in diet from mysids, amphipods, isopods and bregmatocerids to larger Gnathophis sp., Mursia cristimanus and carid shrimps. Large discrepancies were seen in the diet of animals spatially, temporally and between research and commercially-caught animals. Disc-width frequency data was limited but suggested that both species show preference for depths of 100-300m. Size distribution did not appear to be affected by depth, although the data set was limited. A paucity of large individuals in the catch may indicate that stocks are suffering from growth overfishing by trawling operations. Historical and observer data showed that although skates are common components of the by-catch, the potential for greater use is limited. The biscuit skate, R.straeleni, on the west coast is the only species that could be better utilized. If skates are treated as a single group the potential is increased but this causes problems in assessing stocks.
- Full Text:
- Date Issued: 1997
The biophysical dynamics of the Lower Shire River Floodplain fisheries in Malawi
- Authors: Chimatiro, Sloans Kalumba
- Date: 2005
- Subjects: Shire River Valley (Malawi and Mozambique) Fisheries -- Malawi
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5243 , http://hdl.handle.net/10962/d1005086
- Description: Fishes of African floodplains typically comprise populations having short life cycles, relatively few age groups, more generalised feeding behaviour, and which experience spawning success that is strongly influenced by abiotic factors such as hydrological regime of the river, climatic seasonality and habitat characteristics. In addition, African river-floodplain ecosystems do not have appropriate predictive models for estimating yield in these ecosystems. While most predictive models developed to date for floodplain fisheries have taken into account morpho-edaphic factors, they have generally excluded climatic factors as a mega-determinant of the variability of floodplain fisheries. The principle aim of this thesis has been to develop a predictive management model that incorporates data on essential biological aspects of the target species, characteristics of the habitat as well as overall climatic factors, and thus allow for adaptive management of the fisheries in a continuously fluctuating floodplain environment. Lower Shire Floodplain (34 ⁰ 45’ – 35 ⁰ E and 16 ⁰ 00’-17 ⁰ 15’ S) in Malawi, one of the major rivers-floodplains in the Zambezi Basin, was used to test this type of model. The major hypothesis tested in this study was that “the dynamics of the fishery of Lower Shire Floodplain are driven by and adapted to the seasonal, but predictable, hydro-climatic regime of the floodplain”. The specific objectives were: to describe the floodplain’s climate and hydrological pattern; to develop a quantitative characterisation of the major habitats of the Lower Shire Floodplain; to assess the fishery in terms of size, gear utilisation, gear selectivity and yield; to assess the biological parameters of the target species, necessary for the management of the fishery; to analyse how water fluctuation in the floodplain affects the recruitment and life history of the two target species; and to develop of a predictive hydro-climatic model to benefit the management of the fisheries. The climate of the floodplain was characterised by low (765 ± 198 mm) and fairly variable (Cv = 27%) rainfall, which largely occurred between December and January. The area was generally humid (mean RH 68%), with mild to hot (25- 33ºC) and variable monthly mean diurnal (12ºC) temperature. Four quarterly hydro-climatic seasons were identified and comprised: Quarter 1 (Jul-Sep) characterised by hot, dry weather with a low flood regime; Quarter 2 (Oct-Dec) hot, windy, wet weather with low-but-rising flood regime; Quarter 3 (Jan-Mar) hot humid, wet weather with the flood regime at peak; and Quarter 4 (Apr-Jun) humid and cool weather with receding flood regime. The annual hydrograph of the floodplain was represented by four categories of flood regime as: low (Jul-Sept), low-but-rising (Oct-Dec), peak (Jan- Mar), and falling (Apr-Jun). The floodplain experienced a water deficit of 95.1 mm.year⁻¹, and it was hypothesised that ground water recharge maintained water in the floodplain the rest of the year. Three major habitats were identified in the floodplain. The river-floodplain, characterised by deep fast-flowing water, sandy substrate and little emergent vegetation; the permanently connected lagoons, were shallow (≤ 2 m) with sandymud bottom and slow flowing water; and the seasonally connected lagoons had slowflowing stagnant water, with comparatively more emergent and floating vegetation. Physicochemical characteristics of the habitats varied significantly with hydroclimatic seasons (one-way ANOVA, p ≤ 0.05), indicating the influence of flood regime, which joined the habitats in a non-equilibrial spatial distribution. Consequently, during receding and low flood regimes river-floodplain and permanently connected lagoons exhibited similar characteristics while all three habitats had similar characteristics during the rising and peak flood regimes. It was, therefore, concluded that in floodplains, habitats shift horizontally and vertically according to the water level. Gill nets, cast nets, long line, and fish traps accounted for 99% of the total count of gears, and hence considered the major fishing sectors. Two principal species in the floodplain were the catfish Clarias gariepinus and the cichlid Oreochromis mossambicus. Length-at-maximum-selectivity (ø) and length-at-50%-sexual-maturity (Lm₅₀) for each of the two species showed that although they were selected into the four fishing sectors at lengths above maturity, maximum selectivity into the long line occurred at a length before maturity for O. mossambicus. In addition, the width of the gamma selectivity function (σ) indicated that a considerable proportion of juveniles of the two species were also selected. Therefore, it was decided that management for the floodplain be centred on controlling over-fishing and preserving the spawner stock, by banning seine and mosquito nets, and closing river-floodplain and permanently connected lagoons to fishing during the low flood regime. There were significant seasonal variations in CPUE, lowest in the low flood, and highest during the peak flood regime. Sectioned otoliths were used to determine the age and growth of the two principal species in the floodplain. Marginal zone analysis revealed that annulus formation in all the species occurred during the period of low air and water temperatures, high evaporation and receding water levels, hence a high rate of desiccation and negative water budget. For O. mossambicus, maximum age reached was 6 years while in C. gariepinus it was 9 years. The 3-parameter von Bertalanffy growth model adequately described growth as lt = 177.6(1-e⁻·⁴⁴⁽t ⁺ ¹·⁴³⁾) mm TL for O. mossambicus and lt = 502.9(1-e⁻°·³¹⁽t ⁺ ¹·⁹²⁾) mm TL for C. gariepinus. Female O. mossambicus reached 50%-sexual-maturity at 109 mm SL, while males matured at 105 mm, and both male and female C. gariepinus reached Lm₅₀ at 249 mm SL. The breeding seasons of both O. mossambicus and Clarias gariepinus were between September and March, with modal peaks in January and November, respectively. The annual total mortality rates (Z) were 0.62 ± 0.18 yr⁻¹ for O. mossambicus and 0.93 ± 0.47 yr⁻¹ for C. gariepinus. The mean empirical estimates of natural mortality (M) were 0.46 yr⁻¹ for O. mossambicus and 0.50 year⁻¹ for C. gariepinus, and fishing mortality (F) was calculated as 0.16 yr⁻¹ for O. mossambicus and 0.43 yr⁻¹ for C. gariepinus. The overall exploitation level (Z/K) was 1.41 for O. mossambicus and 3.01 for C. gariepinus. Given that the Z/K ratio was >1, it was asserted that both O. mossambicus and C. gariepinus were mortality-dominated and fairly heavily exploited. However, potential for sustainable exploitation existed since both species showed signs of resilience due short longevity and high rate of natural mortality. Given the limitation of simple exponential models of fish mortality and growth under the situation of seasonal fluctuation of water levels, a simple predictive hydroclimatic- fisheries model was developed. The model predicted the life-history and production parameters fairly accurately (0.53 ≤ r² ≥ 0.98, p ≤ 0.05), and showed that environmental and biological events in the floodplain significantly (0.43 ≤ r² ≥ 0.91, p ≤ 0.05) followed the periodic function of time (day-of-the-year), hence, strongly seasonal. In addition, the flood-pulse preceded all the major biological events, with predicted phase lags established at 55.6º for peak flood, 157.2º, 260.1º, 334.6º and 341.4º for condition factor for O. mossambicus, recruitment, spawning period for O. mossambicus and C. gariepinus, respectively. Therefore, it was recommended that water obstruction on the Shire River must ensure sufficient water flow during the peak flood and spawning period to allow flooding and inundation of the floodplain in order to create habitat favourable for spawning and feeding as well as improve recruitment.
- Full Text:
- Date Issued: 2005
The chemistry of a new water-recirculation aquaculture system with emphasis on the influence of ozone on water quality
- Authors: Stobart, Michael David
- Date: 1992
- Subjects: Water quality -- Environmental aspects -- Testing , Ozone -- Physiological effect , Aquatic ecology , Aquaculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5244 , http://hdl.handle.net/10962/d1005087 , Water quality -- Environmental aspects -- Testing , Ozone -- Physiological effect , Aquatic ecology , Aquaculture
- Description: Water quality changes that occur during establishment and maintenance of nitrification in two identical recirculating aquaculture systems containing rainbow trout are described. The time taken for the nitrification process to become established was 40-45 days. Mortality of fish attributed to elevated nitrite concentrations were recorded during the initial conditioning phase of the systems. Un-ionised ammonia concentrations did not attain lethal levels during this period. Nitrate concentrations accumulated slowly throughout the study, while the pH and alkalinity of the water decreased with progressive nitrification. Levels of carbon dioxide, calcium, dissolved and suspended solids remained relatively stable until the carrying capacity of the systems was increased, upon which they increased rapidly and general water quality deteriorated. Permanently elevated concentrations of ammonia and nitrite served as an indication that the carrying capacity of the systems had been exceeded. The use of ozone as a water enhancement treatment in aquaculture systems during one- and six-hour applications was also considered in this study. Ozonation significantly reduced nitrite levels at · low concentrations (0,1 - 0,15 mg/l), although they returned to pre-treatment levels within a few hours of cessation of the treatment. The formation of an unstable, intermediate product that reforms as nitrite in the absence of ozone, rather than the complete oxidation of nitrite to nitrate, is proposed. Ozonation also resulted in decreased dissolved solids, and improved the clarity and odour of the water. Ozone had no effect on ammonia concentrations (at pH > 7,0), or on nitrate or calcium levels, and did not conclusively increase the redox potential of the water. Residual ozone concentrations up to 0,04 mg/l in a sixhour treatment had no harmful effects on rainbow trout, and there were no signs of gas-bubble disease arising from supersaturation of the water with oxygen. Activated carbon filters were effective at removing residual ozone from the water after treatment. Treatment of the water with oxygen alone had no effect on nitrite concentrations.
- Full Text:
- Date Issued: 1992
The conservation and management of freshwater fishes in the Greater Addo Elephant National Park
- Authors: Traas, Graham Ronald Louis
- Date: 2009
- Subjects: Addo Elephant National Park (South Africa) , Freshwater fishes -- South Africa -- Eastern Cape , Fishery conservation -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5247 , http://hdl.handle.net/10962/d1005090 , Addo Elephant National Park (South Africa) , Freshwater fishes -- South Africa -- Eastern Cape , Fishery conservation -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape
- Description: Freshwater fish are the most imperilled vertebrate group with a high projected extinction rate. In general, the world's freshwater ichthyofauna is in a poor state and is threatened by habitat destruction, pollution, the effects of alien species, damming, water extraction and overfishing. Within South Africa, legislation supporting the conservation of aquatic habitats and its associated fauna is strong, but there is a lack of capacity and poor co-ordination between agencies responsible for the conservation and management. The Greater Addo Elephant National Park (GAENP) includes the upper catchments of five of the Sundays River tributaries. Since the optimal method of conserving freshwater aquatic biota is to conserve the headwaters of either the river or its tributaries, there is an opportunity to conserve the native ichthyofauna of the Sundays River system. The principal objective of this thesis was, therefore, to provide information pertinent to the conservation and management of the fishes in the Sundays River system. Sixteen species of freshwater and estuarine fish were sampled, of which eight were alien. Species composition in each of the rivers, with the exception of the Kabouga River, had changed significantly from previous studies. The distribution ranges of several indigenous species had reduced, while those of some alien species was increased. Two species not previously recorded, Labeo capensis and Gambusia affinis, were sampled. Alien species were sampled from all the tributaries. Diversity indices and community assemblage models were identified as approaches for monitoring the ichthyofauna in this species depauperate system. Diversity indices were not recommended for use as a monitoring tool, as they provided insufficient detail on community composition and structure. A modified depletion estimator was applied to multiple pass electrofishing data to determine the effects of various physico-chemical variables on the absolute abundance of Pseudobarbus afer, an endangered species. Pseudobarbus afer density was found to be positively correlated to the presence of boulders. Where P. afer were present, they were abundant. Of the total sampled catch, 21.8% was comprised of alien fishes. Clarias gariepinus was the most successful invader having penetrated all but one of the tributaries. Micropterus salmoides changed the species composition of the Wit River significantly through predation, and is potentially the most dangerous of the alien species in the Sundays River system, capable of extirpating a population of P. afer in as little as three days. Only one man-made barrier to the upstream migration of alien fishes was present on the tributaries, and several addition barriers are required to safeguard the populations of indigenous fish in the headwaters of these tributaries. Several management and conservation tools are presented and discussed, including river rehabilitation, translocation, eradication of alien species, erection of barrier weirs and captive breeding programmes. Public awareness and education is stressed because without support from the communities surrounding the GAENP, management plans for conservation of the indigenous ichthyofauna will, in all likelihood, fail.
- Full Text:
- Date Issued: 2009
The cryopreservation potential and ultrastructure of Agulhas sole Austroglossus pectoralis spermatozoa
- Authors: Markovina, Michael Zeljan
- Date: 2008
- Subjects: Spermatozoa , Spermatozoa -- Cryopreservation , Aquaculture , Fishes -- Breeding , Soleidae , Flatfishes , Agulhas Current (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5251 , http://hdl.handle.net/10962/d1005094 , Spermatozoa , Spermatozoa -- Cryopreservation , Aquaculture , Fishes -- Breeding , Soleidae , Flatfishes , Agulhas Current (South Africa)
- Description: As the estimated market demand for the Agulhas sole Austroglossus pectoralis exceeds the annual catch from trawlers, this species is a potential aquaculture candidate. Broodstock conditioning and gamete preservation is part of research and development aiming at establishing a breeding protocol for a new aquaculture species. Based on a literature review of the morphology of pleuronectiform spermatozoa, this study was designed firstly, to contribute to the field of spermatozoan morphology by describing the ultrastructure of A. pectoralis spermatozoa. This was followed by an experiment to cryopreserve mature spermatozoa to provide baseline data for future studies on this and related species. The testis of A. pectoralis was a paired structure encased in a membrane, the tunica albuginea. The primary testis was located on the dorsal surface of the rib cage and the secondary testis on the ventral side. The testis was of an unrestricted spermatogonial type, based upon observations of spermatogonia along the entire length of the lobule. Mature spermatozoa of A. pectoralis had an acrosome-free ovoid head 1.68 ± 1.6μm in length and 1.7 ± 1.6μm in diameter, a short mid-piece of 0.5 ± 0.1μm in length, containing 7 irregularly shaped mitochondria forming a ring-like structure at the base of the nucleus. The flagellae were 47.4 ± 4.8μm in length, most with two plasma membrane lateral fin-like projections. However, some flagellae had either zero or three lateral fin projections. Cross-sections of the flagellae showed an axenome with a 9+2 microtubule configuration. The proximal and distal centriols were coaxal, situated deep within the nuclear fossa. The structure of A. pectoralis spermatozoa conformed to the type 1 ect-aquasperm, also found in externally fertilizing species. This type has been suggested to be the plesiomorphic form in Neopterigians. Finally, this study contributed to a cryopreservation protocol for A. pectoralis spermatozoa by testing the two cryoprotectants dimethyl sulphoxide (DMSO) and glycerol. Glycerol, at a concentration of 10%, offered better cryoprotection than DMSO. This was established using flow cytometry analysis of post-thaw nuclear membrane integrity after 64 days of storage in liquid nitrogen. The toxicity of DMSO to isolated cellular proteins may have resulted in DMSO-treated sperm having the highest percent (35.2% ± 3.2%) of non-viable cells compared with 23.0% ± 2.5% and 27.8% ± 3.4% for glycerol and the control, respectively. The presence of sucrose in the Modified Mounib Medium extender solution may explain why 45.5% ± 5% of the sperm cells were potentially viable in the control treatment. Initially, the white margined sole Dagatichthys marginatus (Soleidae) was selected as the most suitable candidate for flatfish aquaculture in South Africa. Thus, the aim of this study was to investigate the cryogenic potential and ultrastructure of D. marginatus spermatozoa. However, due to a skewed sex ratio, there were not enough males available to study this species. A skewed sex ratio is common amongst soleids, thus, the need to develop effective cryopreservation methods and to develop an understanding of sperm morphology so that the best time for cryopreservation can be chosen. In conclusion, this first description of spermatozan morphology of A. pectoralis contributed to our understanding of soleid sperm ultrastructure. In addition, a comparison of testis appearance between fish sampled just prior to spawning season and fish with mature sperm provided information on the spawning season of this species. The findings from the cryopreservation experiment suggested that glycerol was a feasible cryoprotectant for this species when sperm was prepared under field conditions.
- Full Text:
- Date Issued: 2008
The demography, breeding biology and management of two mullet species (Pisces : Mugilidae) in the Eastern Cape, South Africa
- Authors: Bok, Anton
- Date: 1984
- Subjects: Fishes -- South Africa -- Eastern Cape Mullidae -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5213 , http://hdl.handle.net/10962/d1004931
- Description: Aspects of the life history of Myxus capensis which were likely to be most affected by man-induced habitat changes, were studied in the eastern Cape. Myxus capensis was found to be specialized for a catadromous life history. The fry migrate into freshwater reaches of rivers within a few months of being spawned at sea and return to an estuarine or marine environment when maximum size has been attained and large energy reserves necessary for spawning have been accumulated. Myxus capensis penetrates considerable distances up eastern Cape rivers and although present in the upper reaches of some estuaries, is only common in freshwater-dominated systems. Myxus capensis has adapted its life history style in a number of ways to overcome the constraints associated with the spatial separation of the freshwater feeding areas and the marine spawning grounds in a region prone to droughts and erratic river flow. Research on the more estuarine-dependent Mugil cephalus, which is also found in the freshwater reaches of eastern Cape rivers, enabled useful comparisons to be drawn. As the latter species is not dependent on a freshwater phase in its life cycle, it is subject to different selection pressures. This comparative approach gave insights into the adaptive significance of the life history tactics of Myxus capensis. Myxus capensis displays a number of life history tactics characteristic of migratory fish species which are thought to increase population fecundity by increasing the number of large females and hence maximizing egg production. These include a sex ratio in favour of females, faster female growth, females remaining longer in the freshwater feeding areas and reaching a larger ultimate size. Possible adaptations to the periodic isolation of the feeding and spawning areas include: (i) the development of ripe gonads only in estuarine or marine areas when access to the spawning grounds is ensured; (ii) year-round spawning and hence recruitment which enables the erratic floods to be used at any time for downriver spawning migrations and reduces the chances of total recruitment failure due to short-term adverse environmental conditions and (iii) a relatively wide range of size and age at first (and final) sexual maturity (2+ to 5+ years); this tends to ensure successful reproduction and recruitment in spite of a series of poor years, as well as dampen population fluctuations after long periods of isolation in fresh water. The dependence of Myxus capensis on the freshwater reaches of eastern Cape rivers makes this species vulnerable to man-induced habitat changes. The erection of barriers to migration has cut off large stretches of suitable habitat and almost completely eliminated Myxus capensis from certain rivers. This detrimental effect has been largely responsible for the recent inclusion of this species on the Red Data list of endangered fish species in South Africa. This study demonstrated the considerable fisheries potential of both mullet species and this should ensure that their conservation and wise utilization be given high priority. Management proposals include: (i) the netting and lifting of Myxus capensis over barriers to migration; (ii) the construction of fish ladders when feasible and (iii) the artificial propagation of this species to enable large-scale stockings of existing man-made impoundments as well as natural habitats to be carried out. It is predicted that the life history characteristics of Myxus capensis, which evolved in response to an erratic freshwater environment, should ensure that when man-induced habitat changes are rectified, this species will again flourish in eastern Cape rivers.
- Full Text:
- Date Issued: 1984
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
The development of a geographic information systems based atlas of southern African freshwater fish, and its application to biogeographic analysis
- Authors: Scott, Lucy Elizabeth Powell
- Date: 2000
- Subjects: Freshwater fishes -- Africa, Southern , Freshwater fishes -- Geographical distribution -- Atlases , Freshwater fishes -- Africa, Southern -- Geographical distribution -- Atlases , Geographic information systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5256 , http://hdl.handle.net/10962/d1005099 , Freshwater fishes -- Africa, Southern , Freshwater fishes -- Geographical distribution -- Atlases , Freshwater fishes -- Africa, Southern -- Geographical distribution -- Atlases , Geographic information systems
- Description: A Geographic Information Systems (GIS) atlas of southern African freshwater fish was developed for the SADC countries from natural history collection specimens, hydrological, topographical and climatological data. The primary purpose of the development of the atlas of freshwater fish was the construction of a practical framework to transform vast amounts of existing biological data for use in research and management of aquatic resources. The database of freshwater fish collection specimens that was incorporated into the atlas, was developed in association with ALCOM (Aquatic Resources Management for Local Community Development Programme). The development of advanced computing and GIS technology has increased the scope of biological atlas projects by facilitating the integration of large amounts of spatial data to produce derived databases for specific applications. The atlas of freshwater fish was constructed using TNTmips GIS software as the most practical system available for managing and analysing biological data with a spatial component. The atlas contains 35 180 comprehensive distribution records of 735 species of fish. It has many applications as an inventory of ichthyofaunal spatial biodiversity, including those of conservation planning, environmental assessment and biogeographic research. Biogeographic studies have traditionally been subjective due to the logistical problems of working with large amounts of distribution data, although some small-scale quantitative research has been carried out in the past. The content of the atlas of freshwater fish is tested with respect to these previous studies, on known patterns of freshwater fish distributions, and the analytical capability of the atlas is tested and demonstrated with some new preliminary approaches to the analysis of freshwater fish distributions in southern Africa.
- Full Text:
- Date Issued: 2000
The development of a larval feeding regimen for dusky kob, Argyrosomus japonicus, with a specific focus on the effect of weaning period on larval development and survival
- Authors: Keet, Thomas
- Date: 2019
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96897 , vital:31344
- Description: One of the biggest limiting factors in marine finfish aquaculture is the low survival rate of early-stage larvae. Most mortalities can be ascribed to the poor nutritional value of live feeds, sibling cannibalism, and various stressors that result in swim bladder hyperinflation and/or starvation during the larval stage. Research results vary on the best timing for the introduction of artificial feed for good survival and growth rate in dusky kob larvae. The main objective of this experiment was to improve survival and growth rate. The experiment focused on a new feeding regime that sought to wean larvae onto an artificial diet earlier than the current Argyrosomus japonicus standard (weaning commenced at 16 days after hatch (DAH) versus 20 days after hatch), based on findings and recommendations made by Musson & Kaiser (2014). Three trials were conducted, each with five replicates of the two treatments, namely the new feeding regime and the standard feeding regime in a fully randomised design. Samples from each tank were collected every two days for the duration of the trial. Morphometric measurements (standard length; body depth; eye diameter) obtained from these sample larvae were used to compare growth rates between treatments. The ratio of BD:SL was used to assess larval condition throughout each trial. Tank survival rates were calculated on the last day of each trial.The study indicated that in mean water temperatures ranging from 24.3 – 25.2 °C, dusky kob larvae can be weaned onto an artificial pellet diet from 16 - 21 DAH without any negative effects on growth, condition and survival. Results from the highest mean temperatures of Trial 2 show a better mean condition in the treatment group during the weaning period (p < 0.05). In Trial 3, with its lower mean water temperatures of 23.2 °C, larvae in both treatments showed stunted absolute growth rates of all biometrics when compared to results from the higher mean temperatures of Trials 1 and 2. During the first 6 days of Trial 3 larvae were in relatively poor condition, BD:SL ≤ 0.30. During this same period in Trials 1 and 2, mean BD:SL ≥ 0.31, suggesting that a BD:SL ratio of ≤ 0.30 in non-weaned dusky kob larvae is an indicator of a degree of starvation. A future study on the morphology and histology of the larval gastrointestinal tract, specifically the liver and intestines, and how this early weaning regime affects their ontogeny under differing temperature conditions this needed to investigate the validity of these initial data on dusky kob larvae condition.
- Full Text:
- Date Issued: 2019
The development of a larval feeding regimen for dusky kob, Argyrosomus japonicus, with a specific focus on the effect of weaning period on larval development and survival
- Authors: Keet, Thomas
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146577 , vital:38538
- Description: One of the biggest limiting factors in marine finfish aquaculture is the low survival rate of early-stage larvae. Most mortalities can be ascribed to the poor nutritional value of live feeds, sibling cannibalism, and various stressors that result in swim bladder hyperinflation and/or starvation during the larval stage. Research results vary on the best timing for the introduction of artificial feed for good survival and growth rate in dusky kob larvae. The main objective of this experiment was to improve survival and growth rate. The experiment focused on a new feeding regime that sought to wean larvae onto an artificial diet earlier than the current Argyrosomus japonicus standard (weaning commenced at 16 days after hatch (DAH) versus 20 days after hatch), based on findings and recommendations made by Musson & Kaiser (2014). Three trials were conducted, each with five replicates of the two treatments, namely the new feeding regime and the standard feeding regime in a fully randomised design. Samples from each tank were collected every two days for the duration of the trial. Morphometric measurements (standard length; body depth; eye diameter) obtained from these sample larvae were used to compare growth rates between treatments. The ratio of BD:SL was used to assess larval condition throughout each trial. Tank survival rates were calculated on the last day of each trial.The study indicated that in mean water temperatures ranging from 24.3 – 25.2 °C, dusky kob larvae can be weaned onto an artificial pellet diet from 16 - 21 DAH without any negative effects on growth, condition and survival. Results from the highest mean temperatures of Trial 2 show a better mean condition in the treatment group during the weaning period (p < 0.05). In Trial 3, with its lower mean water temperatures of 23.2 °C, larvae in both treatments showed stunted absolute growth rates of all biometrics when compared to results from the higher mean temperatures of Trials 1 and 2. During the first 6 days of Trial 3 larvae were in relatively poor condition, BD:SL ≤ 0.30. During this same period in Trials 1 and 2, mean BD:SL ≥ 0.31, suggesting that a BD:SL ratio of ≤ 0.30 in non-weaned dusky kob larvae is an indicator of a degree of starvation. A future study on the morphology and histology of the larval gastrointestinal tract, specifically the liver and intestines, and how this early weaning regime affects their ontogeny under differing temperature conditions this needed to investigate the validity of these initial data on dusky kob larvae condition.
- Full Text:
- Date Issued: 2019
The development of a practical diet for juvenile dusky kob, Argyrosomus japonicus, for the South African mariculture industry
- Authors: Woolley, Lindsey
- Date: 2009
- Subjects: Fishes -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Argyrosomus -- Nutrition , Sciaenidae -- Nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5257 , http://hdl.handle.net/10962/d1005100 , Fishes -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Argyrosomus -- Nutrition , Sciaenidae -- Nutrition
- Description: The lack of locally manufactured marine finfish diets motivated the current project, which aimed to develop a practical diet specifically formulated for dusky kob. The first growth trial investigated the effect of pellet texture (i.e. hard versus soft pellets) and the inclusion of an additional binder, test treatments were compared to two reference diets. There was no significant difference in weight gain between fish fed the hard or soft pellets (p=0.17), over nine weeks. The fish fed the local trout feed weighed significantly less than those fed the test diets (p=0.003). There was no significant difference in leaching rate amongst treatments (p=0.45). A hard pelleted diet without gelatin is recommended in the commercial culture of dusky kob. Pellets with different physical shapes were tested to determine the effect of shape on settling speeds. A square shaped pellet had a slower sinking rate compared to a round shaped pellet (p<0.0001). Juvenile dusky kob, held in cages, fed the square pellets grew significantly faster than the fish fed the round pellet, with a mean weight gain of 16.81 ± 0.45 g (p=0.018). A growth trial was used to optimize the protein to energy (PE) ratio by adjusting dietary protein and lipid levels. Fish fed the diets with high levels of protein (46 % protein) achieved the better growth rates (125 % weight gain) compared to the lower protein diets (92 % weight gain) (p<0.0001). There was no significant difference in total ammonia production (TAN) level for the 46 and 42 % protein diets (p=0.68). The overall performance of the prototype diet was investigated in a closed recirculating system. Growth and FCR of the fish fed the prototype diet was on a par to those fed the commercially available diet currently used in the local farming industry. There was no significant difference in the blood chemistry for fish held at increased stocking densities. The prototype diet is suitable for use in recirculating systems, as there were no negative effects on water quality parameters. This study has laid a foundation for the manufacture of a practical commercial dusky kob diet in South Africa.
- Full Text:
- Date Issued: 2009
The development of an ecological model to determine flood release options for the management of the Phongolo floodplain in Kwazulu/Natal (South Africa)
- Authors: Weldrick, Sarah Katharine
- Date: 1996
- Subjects: Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5258 , http://hdl.handle.net/10962/d1005102 , Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Description: The Phongolo River floodplain in KwaZulu/Natal is a river-associated wetland which was subject to regular cycles of flooding in the past. The floods were associated with seasonal summer rainfall. Through the wet and dry cycles on the floodplain there was an alternation between the aquatic and terrestrial biomes. Many of the fishes on the floodplain are dependent on this cycle for their survival. The construction of the Pongolapoort Dam in 1969 has resulted in alterations to the timing, magnitudes and duration of the natural flooding events of the Phongolo River. This alteration has affected the fisheries. It is now necessary to simulate natural floods by artificial water releases from the dam. There are several demands on the water supply, so it has not always been possible to adhere to the natural flood regime. This necessitated the need for an integrated management programme to ensure the sustainability of the natural resources. A practical ecological model of the fishery was developed to determine an optimum flood release scenario for the floodplain. The relative abundances, distribution and species richness of the fishes were determined at various lakes and rivers on the floodplain. A community classification of the fishes was determined using TWINSPAN ordination. The potential yield of the fish at each site was calculated. Flood releases of varying magnitudes were simulated using Geographic Information Systems (GIS). This information was combined in a model which can be used by resource managers to estimate the percentage species compositions of fishes at each of the lakes, and to compare the actual harvest to the potential calculated sustainable yields of fishes for various flood release regimes. Subsistence agriculture and other beneficial ecological information can be incorporated into the model to determine the effect of different flood release options for the Phongolo floodplain.
- Full Text:
- Date Issued: 1996
The distribution patterns and community structure of the Tsitsikamma rocky littoral ichthyofauna
- Authors: Burger, Lynton Francois
- Date: 1991
- Subjects: Fishes -- South Africa -- Geographical distribution , Tripterygiidae -- South Africa -- Geographical distribution , Littoral plants -- South Africa -- Tsitsikamma , Littoral plants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5260 , http://hdl.handle.net/10962/d1005104 , Fishes -- South Africa -- Geographical distribution , Tripterygiidae -- South Africa -- Geographical distribution , Littoral plants -- South Africa -- Tsitsikamma , Littoral plants
- Description: The results of a community survey of the rocky intertidal and subtidal reef ichthyofauna of the Tsitsikamma National Park and adjacent areas are presented. An updated species checklist is given, comprising 116 species of 46 families, including a new genus and species of Tripterygiid. Single species are shown to dominate, in terms of numbers, both the cryptic and subtidal components for all the areas sampled down the vertical profile. Species richness, evenness and diversity are found to increase with depth for both the cryptic and suprabenthic components. A community level feeding study shows an increase in trophic specialisation with depth and food availability is found to be an important factor delimiting littoral fish vertical distribution. The nursery function of the Tsitsikamma rocky littoral area is assessed and it is shown that shallow littoral areas as a whole are more important than intertidal pools alone in functioning as nurseries. The results of the study are found to fit into the existing trend of an increase in species richness and diversity, from west to east, along the South African coast. A significant difference is shown between the observed frequencies of species on exploited reefs outside the Park and unexploited reefs inside the Park. The density of the key reef predator Petrus rupestris is shown to be nine times more abundant on deep reef inside the park compared to deep reef outside the park (0.0045 fish/m² and 0.0005 fish/m² respectively) and a paucity of larger individuals of this species on exploited reefs is noted. Marked differences in the relative abundance of other species between exploited and unexploited reefs are evident and it is hypothesised that community disruption has occurred on exploited reefs, either directly or indirectly because of the removal of P. rupestris. These results are discussed in the context of marine reserves as a conservation strategy and a recommendation is made to extend the 5.6km seaward boundary of the Tsitsikamma National Park westwards to include the large concentration of presently exploited rocky reefs between the Blaaukrans river mouth and Natures Valley.
- Full Text:
- Date Issued: 1991
The dynamics of a subtropical lake fishery in central Mozambique
- Authors: Weyl, Olaf L F
- Date: 1999
- Subjects: Fisheries -- Chicamba, Lake Fisheries -- Mozambique
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5212 , http://hdl.handle.net/10962/d1004785
- Description: Fisheries in African reservoirs are typically multi -species and in most cases the fish resource is harvested with a number of gears. These characteristics complicate their management and the development of management procedures. Typically, long time series of data on catch and effort and length- or age-based catch are not available for these fisheries. This precludes the use of data intensive methods such as multi-species virtual population analysis. The principal aim of this thesis was to develop a management procedure for African reservoir fisheries that takes into account the pertinent biological characteristics of the target species and accounts for the multi-species and multi-gear irIteractions in such fisheries. An opportunity availed itself to undertake this work on Lake ChicaIllba (19°08'S 33°08'E) a man-made hydroelectric dam in subtropical Mozambique (Manica province). The specific objectives of this study were: to obtain locality specific biological parameters for the target species in Lake ChicaIllba; to assess gear utilisation trends in the fishery through the determination of gear-selectivity, catch rate and effort for each of the principal gears used in the fishery; to assess the fishery using traditional per-recruit models and to test existing and new per-recruit models that account for the multi-species and multi-gear nature of the fishery and to determine the adequacy of each of these approaches in the determination of suitable target reference point (TRP) exploitation rates. The three principal specIes in Lake Chicamba are the introduced largemouth bass, Micropterus salmoides, and two cichlids the Mozambique tilapia, Oreochromis mossambicus and the redbreast tilapia, Tilapia rendalli. Sectioned otoliths were used for age and growth determination. Marginal zone analysis showed that annulus formation in all three species occurred during winter. The maximum-recorded age was 5 years for M. salmoides, 16 years for T. rendalli and 10 years for O. mossambicus. Growth of the three species was best described by the 3 parameter von Bertalanffy growth model as ℓa = 465.51 (1 - e⁻ₑ·ₑ⁷⁵⁽a⁺⁰·⁰⁰⁹⁾ mm FL for M salmoides; ℓa = 238.74 (1 - e⁻⁰⁶³⁶⁽a⁺⁰·⁹⁰⁵⁾) mm TL for T. rendalli; and ℓa = 266.06 (1 - e⁻⁰⁷⁹⁰⁴⁽a⁺⁰·²⁶⁹⁾) mm TL for 0. mossambicus. Female T. rendalli attained 50%-maturity at 2.89 years, while O. mossambicus matured at 2.83 years and M. salmoides at 0.9 years. Both cichlid species spawned throughout summer while M. salmoides had a very short spawning season from August to September. The total annual mortality rate (Z) for M. salmoides in Lake Chicamba was 1.27 yr⁻¹, the mean empirical estimate of natural mortality (M) was 0.73 yr⁻¹, and fishing mortality (F) was calculated at 0.54 yr⁻¹. For T. rendalli Z = 0.31 yr⁻¹, M = 0.20 yr⁻¹, F = 0.11 yr⁻¹ and for 0. mossambicus Z= 0.62 yr⁻¹, M= 0.38 yr⁻¹, F= 0.24 yr⁻¹. The three species exhibited reproductive traits, which implied a high reliance of recruitment on spawner stock (nest guarding in T. rendalli and M. salmoides and mouthbrooding in O. mossambicus). For this reason it was decided that the cichlid fisheries should be managed using TRPs which maintained the spawner biomass-per-recruit at 50% (FSB50) of pristine levels. However, based on good evidence it was hypothesised that the high rate of fishing mortality helped to maintain the fast growth rate of M. salmoides. It was, therefore, decided to manage this species at a TRP of F SB40. The three most important fishing sectors were the gill-net, seine-net and hook-and-line fisheries. The total catch for 1996 was 223 t. The gill nets selected all three species at a size/age approximating 50%-maturity while the seine-net and hook-and-line fisheries selected mainly juvenile fishes. There was strong evidence to suggest that seine net fishing also disrupted spawning. It was shown that the 'traditional' single-species per-recruit models were unsuitable to assess multi-species and multi-gear reservoir fisheries. Since existing multi-species/multifishery yield-per-recruit models were not capable of defining FsB(x) TRPs, a new multispecies/ multi-fishery spawner-biomass-per-recruit approach was developed. This approach allowed for the simulation of the response of spawner biomass-per-recruit to changes in effort in the three fishery sectors, simultaneously. The models showed that the spawner biomass-per-recruit, at current effort levels, was higher than the suggested TRP for the three species. However, it was shown that an increase of 10% in current total effort would reduce spawner biomass-per-recruit to below the recommended TRP levels. With the closure of the seine-net fishery, gill-net effort could be increased to 338 fishers (340 for management purposes) and effort in the hook-and-line fishery could be increased by 30% before the TRP was reached. To maintain the fish stocks above TRP levels, effort control was considered to be the most effective management method. The main recommendations for Lake Chicamba were to close the seine-net fishery, to limit the gill-net fishery to 340 fishers (using 137-m long x 3-m deep gill nets) and to maintain the open access nature of the hook-and-line fishery. The multi-species/multi-fishery per-recruit approach allows for the meaningful simulation of various scenarios and provides relatively robust management options. In the absence of long time series of effort and age- or length-based catch data, this approach was considered as the most suitable assessment method for multi-species/multi-gear African reservoir fisheries.
- Full Text:
- Date Issued: 1999
The dynamics of space use in some Lake Malawi fishes
- Authors: Robinson, Rosanna Lesley
- Date: 1996
- Subjects: Cichlids -- Nyasa, Lake Fishes -- Malawi Fishes -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5264 , http://hdl.handle.net/10962/d1005108
- Description: Behaviour and space utilisation of rock-dwelling cichlids were observed at Thumbi East Island, Lake Malawi. 1. Males of five species of the mbuna complex held long-term territories. Pseudotropheus elongatus "aggressive" vigorously defended a feeding area and sometimes a spawning site interspecifically, but did not feed in the peripheral part of their territory. Spawning sites of Pseudotropheus zebra, Pseudotropheus tropheops "orange chest", Labeotropheus fuelleborni, and Petrotilapia nigra were interspecifically-defended, while larger mating territories were defended against conspecific neighbours. Feeding areas were shared with many fish and often extended beyond the defended area. There was considerable variation in behaviour and space use within and between species and between times of day. 2. Non-territorial P. zebra used larger ranges than territorial conspecifics, and fed more on plankton, but individuals had preferred benthic feeding areas, often in conspecific territories. These 'floaters' were often aggressive. Both size and relative brightness independently predicted the outcome of aggressive interactions between floaters, and a site-specific dominance hierarchy was suggested, with some individuals appearing to be semi-territorial. 3. Males and females of 21 and 13 species respectively were found to establish temporary breeding territories. Overall breeding seasonality was bimodal, but reproductive timing and territory characteristics differed among species. Temporary territories had a considerable impact on the behaviour and habitat use of all resident mbuna species, even causing abandonment of territories. 4. Non-breeding Protomelas taeniolatus had limited home ranges, and showed little aggression. During the highly-synchronised reproductive season, males defended spawning sites and females fry-guarding territories. Most chases were directed towards the commonest fish, but predators were chased further and faster. Female behaviour changed over the guarding period. Females generally continued territorial defence after the brood had disappeared. Most broods contained fry of different sizes and species. Significant benefits were found for guarding females with clustered territories, but females did not appear to choose sites adjacent to conspecific parental females. 5. Territoriality in fish is taxonomically widespread and may serve several functions according to species, sex and developmental stage. It also varies according to genotype- and phenotype-limited strategies and short term costs and benefits. Territories may be simultaneously multifunctional.
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- Date Issued: 1996
The ecology and culture of the rock catlet Chiloglanis pretoriae (Pisces : mochokidae)
- Authors: De Villiers, Pierre
- Date: 1991
- Subjects: Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5267 , http://hdl.handle.net/10962/d1005111 , Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Description: Chiloglanis pretoriae is a rock catlet, indigenous to southern Africa. The aim of the study was to develop a technique to culture C. pretoriae as an alternative to harvesting and selling wild caught fish on the international aquarium trade. As nothing was known about the culture of African rock catlets an investigation into the biology and ecology of the species was necessary to develop the culture protocol. Chiloglanis pretoriae inhabits fast flowing rapids (current speeds over 0.6 metres per second). It is a serial interstitial gravel spawner, that spawns during the summer months. Chiloglanis pretoriae is a carnivorous fish species, feeding on aquatic insects. The natural growth rate is relatively fast in the first two years where after it levels off. Sexual maturity (50%) is attained within the first year (44mm total length). From the four cell stage, embryos took seven days to hatch, 16 days to first feeding and 75 days to reach the juvenile phase. The free embryos were well developed and readily accepted artificial feed at first feeding. The fish spawned readily, without hormone induction, in a continuous raceway. Spawning in the 801 retangular glass aquaria was irregular. The substrate within the raceway consisted of gravel and large rocks. The current was maintained at 0.6m/sec, temperature at 26± 0.6⁰C, dissolved oxygen concentrations at 7.1± 0.3mg/l, pH at 6.9± 0.2 and photoperiod at 16L:8D. Conductivity was monitored and remained within the acceptable range of C. pretoriae (84± 10uS/m).
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- Date Issued: 1991