Evaluation of Baited Remote Underwater Video Systems (BRUVS) for monitoring fish communities in Lake Malawi/Niassa
- Authors: Van Wyk, Angus
- Date: 2020
- Subjects: Underwater videography -- Malawi , Chambo -- Malawi -- Monitoring , Fishes -- Malawi -- Monitoring , Oreochromis lidole -- Malawi -- Monitoring
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145546 , vital:38448
- Description: Baited Remote Underwater Video systems (BRUVS) have become a well-established in-situ monitoring technique in clearwater aquatic ecosystems. The relatively low cost, nondestructive and non-extractive nature of this technique permits BRUVS to be employed in a wide range of habitats. To date, the vast majority of studies using BRUVS technology have been conducted in marine habitats. Subsequently, BRUVS applications in freshwater habitats are scant, and techniques are not well developed. The primary objective of this thesis was to address this knowledge gap and develop standard operating procedures for BRUVS employment in Lake Malawi/Niassa and explore the potential of BRUVS as a monitoring tool for fish communities in the African Great Lakes. Eight easily identifiable species groups, representative of Lake Malawi/Niassa inshore fish communities, were used to develop the technique. The optimal BRUVS deployment time to obtain 95 % species accumulation was achieved in a 15-minute recording period. Power analysis, using a pre-determined 80 % power, a confidence interval of 95 % and a significance level of < 0.05 was used to determine annual sampling effort requirements for each species group. The power analysis was performed to detect a 10 % change in abundance over a hypothetical 10-year monitoring scenario. In areas where fish abundance was lower, the sampling effort required to monitor key fisheries species was significantly higher. For example, Chambo, the local Oreochromis (Nyasalapia) species flock, required an annual sampling effort of 120 deployments in Malawi compared to 56 in Mozambique ( < 0.05). Chambo had a higher detection probability in areas of lesser fishing pressure and were found in higher abundances in deeper, less accessible habitats. Deep-water (> 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.
- Full Text:
- Date Issued: 2020
- Authors: Van Wyk, Angus
- Date: 2020
- Subjects: Underwater videography -- Malawi , Chambo -- Malawi -- Monitoring , Fishes -- Malawi -- Monitoring , Oreochromis lidole -- Malawi -- Monitoring
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145546 , vital:38448
- Description: Baited Remote Underwater Video systems (BRUVS) have become a well-established in-situ monitoring technique in clearwater aquatic ecosystems. The relatively low cost, nondestructive and non-extractive nature of this technique permits BRUVS to be employed in a wide range of habitats. To date, the vast majority of studies using BRUVS technology have been conducted in marine habitats. Subsequently, BRUVS applications in freshwater habitats are scant, and techniques are not well developed. The primary objective of this thesis was to address this knowledge gap and develop standard operating procedures for BRUVS employment in Lake Malawi/Niassa and explore the potential of BRUVS as a monitoring tool for fish communities in the African Great Lakes. Eight easily identifiable species groups, representative of Lake Malawi/Niassa inshore fish communities, were used to develop the technique. The optimal BRUVS deployment time to obtain 95 % species accumulation was achieved in a 15-minute recording period. Power analysis, using a pre-determined 80 % power, a confidence interval of 95 % and a significance level of < 0.05 was used to determine annual sampling effort requirements for each species group. The power analysis was performed to detect a 10 % change in abundance over a hypothetical 10-year monitoring scenario. In areas where fish abundance was lower, the sampling effort required to monitor key fisheries species was significantly higher. For example, Chambo, the local Oreochromis (Nyasalapia) species flock, required an annual sampling effort of 120 deployments in Malawi compared to 56 in Mozambique ( < 0.05). Chambo had a higher detection probability in areas of lesser fishing pressure and were found in higher abundances in deeper, less accessible habitats. Deep-water (> 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.
- Full Text:
- Date Issued: 2020
Evaluation of fishway designs for use at the ebb and flow region of rivers in the Eastern Cape, South Africa
- Authors: Lewis, Hylton Varian
- Date: 2007
- Subjects: Fishways -- South Africa -- Eastern Cape , Fishways -- Design and construction , Aquatic ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5279 , http://hdl.handle.net/10962/d1005123 , Fishways -- South Africa -- Eastern Cape , Fishways -- Design and construction , Aquatic ecology -- South Africa -- Eastern Cape
- Description: Fishways are devices that are increasingly being used worldwide to assist aquatic biofauna to migrate through man-made barriers such as weirs and large-scale dams that are used for water storage, electricity generation etc. and have a negative impact on both the upstream and downstream movement of aquatic organisms. Fishways are usually low gradient channels with evenly placed chambers which allow such migrating aquatic species minimal stress on their passage over these barriers. Despite the existence of national and regional policies for their provision, their construction has often been inhibited through a lack of local assessment of the available designs, and use of ineffective international designs. As part of a larger national research programme, sponsored by the Water Research Commission, to develop a protocol for fishway design and implementation, this study sought to investigate the suitability of vertical slot and sloping baffle designs to assist the migrations of juvenile catadromic fish species in the ebb and flow region of rivers in the Eastern Cape, South Africa. These fishways were initially tested under controlled conditions at the Experimental Fish Farm at the Department of Ichthyology and Fisheries Science, Rhodes University using various fish species. Using the performance data thus collected they were then installed and monitored in the field for the catadromic Myxus capensis (freshwater mullet) and Monodactylus falciformis (cape moony) migrations during March and November of 2005 at the Kowie River ebb and flow weir. The laboratory tests showed that there was a significantly higher level of migration success in the vertical slot compared with the sloping baffle fishway under all conditions (F=82.157; p<0.001). There was, however, a slow decline in levels of success with increased discharge in the vertical slot fishway. This was in contrast to the sloping baffle design where success increased as discharge increased at a steep gradient (F=74.894; p<0.005). The level of success with the M. capensis was related to the size of the fish for both systems with success increasing from the small to the large fish (F=17.755; p<0.001). For the M. falciformis higher levels of success were found to occur in the vertical slot fishway compared to the sloping baffle fishway (F=11.792; p<0.00086), with no significant differences being found with an increase in discharge. Field data indicated similar trends with higher migration success using the vertical slot fishway. M. capensis were better able to negotiate both devices compared to the M. falciformis and overall levels of success were higher for both species in the field than under laboratory conditions where the migration urge may have declined.
- Full Text:
- Date Issued: 2007
- Authors: Lewis, Hylton Varian
- Date: 2007
- Subjects: Fishways -- South Africa -- Eastern Cape , Fishways -- Design and construction , Aquatic ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5279 , http://hdl.handle.net/10962/d1005123 , Fishways -- South Africa -- Eastern Cape , Fishways -- Design and construction , Aquatic ecology -- South Africa -- Eastern Cape
- Description: Fishways are devices that are increasingly being used worldwide to assist aquatic biofauna to migrate through man-made barriers such as weirs and large-scale dams that are used for water storage, electricity generation etc. and have a negative impact on both the upstream and downstream movement of aquatic organisms. Fishways are usually low gradient channels with evenly placed chambers which allow such migrating aquatic species minimal stress on their passage over these barriers. Despite the existence of national and regional policies for their provision, their construction has often been inhibited through a lack of local assessment of the available designs, and use of ineffective international designs. As part of a larger national research programme, sponsored by the Water Research Commission, to develop a protocol for fishway design and implementation, this study sought to investigate the suitability of vertical slot and sloping baffle designs to assist the migrations of juvenile catadromic fish species in the ebb and flow region of rivers in the Eastern Cape, South Africa. These fishways were initially tested under controlled conditions at the Experimental Fish Farm at the Department of Ichthyology and Fisheries Science, Rhodes University using various fish species. Using the performance data thus collected they were then installed and monitored in the field for the catadromic Myxus capensis (freshwater mullet) and Monodactylus falciformis (cape moony) migrations during March and November of 2005 at the Kowie River ebb and flow weir. The laboratory tests showed that there was a significantly higher level of migration success in the vertical slot compared with the sloping baffle fishway under all conditions (F=82.157; p<0.001). There was, however, a slow decline in levels of success with increased discharge in the vertical slot fishway. This was in contrast to the sloping baffle design where success increased as discharge increased at a steep gradient (F=74.894; p<0.005). The level of success with the M. capensis was related to the size of the fish for both systems with success increasing from the small to the large fish (F=17.755; p<0.001). For the M. falciformis higher levels of success were found to occur in the vertical slot fishway compared to the sloping baffle fishway (F=11.792; p<0.00086), with no significant differences being found with an increase in discharge. Field data indicated similar trends with higher migration success using the vertical slot fishway. M. capensis were better able to negotiate both devices compared to the M. falciformis and overall levels of success were higher for both species in the field than under laboratory conditions where the migration urge may have declined.
- Full Text:
- Date Issued: 2007
Exploitation patterns of the multi species/gear hake (Merluccius capensis and paradoxus) fishery on South Africa's southeast coast
- Authors: Sutton, Glen Robert
- Date: 2000
- Subjects: Fishing -- South Africa , Hake -- South Africa , Merluccius capensis -- South Africa , Merluccius paradoxus -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5280 , http://hdl.handle.net/10962/d1005124 , Fishing -- South Africa , Hake -- South Africa , Merluccius capensis -- South Africa , Merluccius paradoxus -- South Africa
- Description: The motivation for this study was to examine the exploitation patterns of the M. capensis and M. paradoxus hake fisheries on the Southeast Coast, and determine the size and species of hake caught in each of the hand-line, long-line, and trawl methods. The handline hake fishery has increased substantially over the last several years and concerns are beginning to emerge about the impact this will have on the inshore resource collected on the South Coast between August 1998 and July 1999 was used to describe the hand-line method and estimate annual landings. Data on the size and species in longline catches of hake caught during 1997 were already available for this study. Size distributions in trawl catches were determined from commercial category landing data reported by catch weight and depth. The species composition in these catches determined by comparison using RV Afrikana survey data collected in the same depth regions. Location plays a significant role in determining the sizes and species of hake caught by each gear. Hand-lines catch smaller sizes on average than do long-lines, inshore trawls target mainly M. capensis while offshore trawls catch both hake species. A substantial amount of the hand-line hake caught on the South Coast is not reported. Examination of the exploitation patterns reveal that intense trawling pressure is directed at the smaller sized M. paradoxus inhabiting the depth region between 160-400-meters. Inshore trawls discard a large amount of small sized M. capensis within the 100-meter isobath. A preliminary stock assessment on the status of each hake species found that M. paradoxus appears to be over-exploited while M. capensis was in better shape. However, length-based pseudo-cohort analysis, used in this assessment, is critically reliant on having length frequency data from a steady state population in equilibrium. This limits the application of this model for management purposes and this finding is purely theoretical at this stage. Results suggest that each hake species is under a different pattern and level of exploitation and the multi-species nature of hake stocks on the South Coast should be considered in developing optimum management policies. Future work should focus on developing appropriate age/length keys so that an age-based VPA, which is more powerful than the length-based approach, can be applied towards stock assessments on the South Coast. Alternatively, length-data covering a longer period should be compiled and the equilibrium assumption further investigated so that the results from length-based models can be used with more confidence.
- Full Text:
- Date Issued: 2000
- Authors: Sutton, Glen Robert
- Date: 2000
- Subjects: Fishing -- South Africa , Hake -- South Africa , Merluccius capensis -- South Africa , Merluccius paradoxus -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5280 , http://hdl.handle.net/10962/d1005124 , Fishing -- South Africa , Hake -- South Africa , Merluccius capensis -- South Africa , Merluccius paradoxus -- South Africa
- Description: The motivation for this study was to examine the exploitation patterns of the M. capensis and M. paradoxus hake fisheries on the Southeast Coast, and determine the size and species of hake caught in each of the hand-line, long-line, and trawl methods. The handline hake fishery has increased substantially over the last several years and concerns are beginning to emerge about the impact this will have on the inshore resource collected on the South Coast between August 1998 and July 1999 was used to describe the hand-line method and estimate annual landings. Data on the size and species in longline catches of hake caught during 1997 were already available for this study. Size distributions in trawl catches were determined from commercial category landing data reported by catch weight and depth. The species composition in these catches determined by comparison using RV Afrikana survey data collected in the same depth regions. Location plays a significant role in determining the sizes and species of hake caught by each gear. Hand-lines catch smaller sizes on average than do long-lines, inshore trawls target mainly M. capensis while offshore trawls catch both hake species. A substantial amount of the hand-line hake caught on the South Coast is not reported. Examination of the exploitation patterns reveal that intense trawling pressure is directed at the smaller sized M. paradoxus inhabiting the depth region between 160-400-meters. Inshore trawls discard a large amount of small sized M. capensis within the 100-meter isobath. A preliminary stock assessment on the status of each hake species found that M. paradoxus appears to be over-exploited while M. capensis was in better shape. However, length-based pseudo-cohort analysis, used in this assessment, is critically reliant on having length frequency data from a steady state population in equilibrium. This limits the application of this model for management purposes and this finding is purely theoretical at this stage. Results suggest that each hake species is under a different pattern and level of exploitation and the multi-species nature of hake stocks on the South Coast should be considered in developing optimum management policies. Future work should focus on developing appropriate age/length keys so that an age-based VPA, which is more powerful than the length-based approach, can be applied towards stock assessments on the South Coast. Alternatively, length-data covering a longer period should be compiled and the equilibrium assumption further investigated so that the results from length-based models can be used with more confidence.
- Full Text:
- Date Issued: 2000
Factors influencing estuarine and coastal connectivity of an estuarine-dependent fishery species, Pomadasys commersonnii (Haemulidae)
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
Feeding ecology of Bathyclarias nyasensis (Siluroidei: Claridae) from Lake Malawi
- Kaunda, Emmanuel Kamlipe Watson Hawkins
- Authors: Kaunda, Emmanuel Kamlipe Watson Hawkins
- Date: 2001
- Subjects: Fishes -- Malawi Fishes -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5282 , http://hdl.handle.net/10962/d1005126
- Description: In Malawi, fish contribute about 60-80% to the country's animal protein supply. The greater proportion (> 50%) comes from Lake Malawi. Bathyclarias nyasensis and other clariid catfish contribute up to > 20% of the total catches. Catches of Bathyclarias nyasensis in the inshore area of the south-east arm of Lake Malawi are declining and a management plan for the fishery is essentially lacking. There is paucity of biological data that precludes the use of any option to manage the species. The principal aim of the thesis was to define the ecological role B. nyasensis, the most abundant and common of the Bathyclarias species. By examining life history characteristics within a food web context, it was hypothesized that the study would provide an insight into the interrelationships between species, and, hence form the basis for the development of a rational exploitation strategy for the species. The study was undertaken in the south-east arm of Lake Malawi (9° 30'S, 14° 30'S). The principal objectives of the study were to investigate the feeding ecology of B. nyasensis by examining morphological characters and structures associated with feeding, diet of B. nyasensis, food assimilated in the species using carbon (∂¹³C) isotope analysis, daily food consumption rate for B. nyasensis; and to relate the feeding ecology to life history traits such as age, growth, and some aspects of the reproductive biology of B. nyasensis. The suitability of sectioned pectoral spines and sagittal otoliths to age B. nyasensis was assessed. Due to reabsorption of growth zones with increasing spine lumen diameter with fish size, and the relatively low number of spines that could be aged reliably, only otoliths were used. The maximum age for B. nyasensis was estimated at 14 vears. Growth was best was described by the four parameter Schnute mc: lt ={42+(81¹·⁸ - 42¹·⁸)x1-e⁻°·°⁵⁽t⁻¹⁾}¹/¹·⁸ over 1-e⁻⁽⁻°·°⁵⁾⁽¹¹⁾ for female, lt={41+(98¹·² - 41¹·²)x 1-e⁻°·°²⁽t⁻¹⁾}¹/¹·² over 1-e⁻⁽⁻°·°²⁾⁽¹³⁾ and for male fish. Age-at-50% maturity for females and males were estimated at 7 years and 4 years, respectively. Typically, fish grew rapidly in the first year, but slower during subsequent years. Smaller fish were found inshore while larger fish were found in offshore regions. It was hypothesised that the rapid growth in the first year and slower growth later is a consequence of change in diet from high quality and abundant food source to a more dilute food and that this may be associated with a shift in habitat. Morphological characters associated with feeding were used to predict the food and feeding behaviour of B. nyasensis. The size of premaxillary, vomerine, pharyngeal dental and palatine teeth and premaxillary and vomerine tooth plates suggested the capability of B. nyasensis to handle both large and small prey, with a propensity towards smaller prey in composition to C. gariepinus. The molariform teeth on the vomerine tooth plate suggested that molluscs form part of the diet. The relative gut length (1.27±0.24) suggested omnivory, with an ability to switch between planktivory and piscivory. Buccal cavity volume and filtering area changed with fish size at 500-600 mm TL upon which it was hypothesised that the fish diet changed to planktivory at this size. Detailed diet analysis provided information upon which the above hypotheses could be accepted. Percent Index of Relative Importance (%IRI) and a multi-way contingency table analysis based on log-linear models were used to analyse diet data. Results showed that B. nyasensis is omnivorous, but with a distinct ontogenetic dietary shift from piscivory to zooplanktivory at 500 - 600 mm TL. The increased buccal cavity volume at the same fish size therefore, suggests that B. nyasensis is well adapted to filter the dilute zooplankton resource. Increased foraging costs of feeding on zooplankton explained the slower growth of larger fish. The dietary shift was finally corroborated by results of the ∂¹³C isotope analysis. A polynomial equation described the change in carbon ratios with fish size: ∂¹³C = - 33.188 + 0.4997L - 0.0045 (total length)² (r² = 0.598, n = 12, p=0.022). The ontogenetic shift in diet was synchronised with a habitat shift postulated in life history studies. In the inshore region, B. nyasensis were predominantly piscivorous (apex predators), and were zooplanktivorous in the offshore region, thereby forming part of the pelagic food web in the latter region. After examining "bottom-up" and trophic cascade theories, it was postulated that perturbations of the B. nyasensis stock would be discernible both at the top and lower trophic levels. As a piscivore and therefore apex predator, effects of overfishing B. nyasensis in the inshore region could cascade to unpredictable ecological changes in inshore areas and, due to the ontogenetic habitat shift, in the offshore regions. Examples of trophic cascade phenomena are provided. On the basis of the feeding study, it was possible to reconstruct the pelagic food web of Lake Malawi. Apart from the lakefly Chaoborus edulis, B. nyasensis is the other predator that preys heavily on zooplankton in the pelagic zone. Perturbations of the B. nyasensis stock could affect size composition of zooplankton which in tum, could affect production of C. edulis, a resource for the top predators in the food web. The findings of the present study contributed to the ongoing debate of introducing a zooplanktivore into the pelagic zone of Lake Malawi. Proponents for the introductions have argued that zooplankton predation by fish is inferior to that of C. edulis. Introduction of a clupeid zooplankton was proposed as a strategy to boost fish production in the lake. The zooplanktivore would either out-compete or prey on C. edulis to extinction. Opponents to this view argued that zooplankton biomass in the pelagic region was too low to support introductions and that the fish biomass in the pelagic region may have been underestimated. Results from the present study suggest that planktivorous fish (including B. nyasensis) might not be inferior to C. edulis in utilising the zooplankton resource; B. nyasensis is well adapted to utilise the dilute zooplankton resource, and by omitting B. nyasensis from previous studies, overall zooplankton predation by fish may have been underestimated by between 7 - 33%. On the basis of the theoretical migratory life history cycle of B. nyasensis, it is recommended that the current interest in increasing fishing effort in offshore areas should proceed with caution. Ecological changes that may have occurred in the inshore areas due to overfishing have probably not been noticed: as the offshore zone has never been fished. The latter zone may have acted as a stock refuge area. Higher fishing intensity in the offshore areas could lead to serious ecological imbalances and instability. The study has shown that life history characteristics studied in the context of the food web, and in the absence of other fisheries information and/or data, strongly advocates the precautionary principle to managing changes in exploitation patterns.
- Full Text:
- Date Issued: 2001
- Authors: Kaunda, Emmanuel Kamlipe Watson Hawkins
- Date: 2001
- Subjects: Fishes -- Malawi Fishes -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5282 , http://hdl.handle.net/10962/d1005126
- Description: In Malawi, fish contribute about 60-80% to the country's animal protein supply. The greater proportion (> 50%) comes from Lake Malawi. Bathyclarias nyasensis and other clariid catfish contribute up to > 20% of the total catches. Catches of Bathyclarias nyasensis in the inshore area of the south-east arm of Lake Malawi are declining and a management plan for the fishery is essentially lacking. There is paucity of biological data that precludes the use of any option to manage the species. The principal aim of the thesis was to define the ecological role B. nyasensis, the most abundant and common of the Bathyclarias species. By examining life history characteristics within a food web context, it was hypothesized that the study would provide an insight into the interrelationships between species, and, hence form the basis for the development of a rational exploitation strategy for the species. The study was undertaken in the south-east arm of Lake Malawi (9° 30'S, 14° 30'S). The principal objectives of the study were to investigate the feeding ecology of B. nyasensis by examining morphological characters and structures associated with feeding, diet of B. nyasensis, food assimilated in the species using carbon (∂¹³C) isotope analysis, daily food consumption rate for B. nyasensis; and to relate the feeding ecology to life history traits such as age, growth, and some aspects of the reproductive biology of B. nyasensis. The suitability of sectioned pectoral spines and sagittal otoliths to age B. nyasensis was assessed. Due to reabsorption of growth zones with increasing spine lumen diameter with fish size, and the relatively low number of spines that could be aged reliably, only otoliths were used. The maximum age for B. nyasensis was estimated at 14 vears. Growth was best was described by the four parameter Schnute mc: lt ={42+(81¹·⁸ - 42¹·⁸)x1-e⁻°·°⁵⁽t⁻¹⁾}¹/¹·⁸ over 1-e⁻⁽⁻°·°⁵⁾⁽¹¹⁾ for female, lt={41+(98¹·² - 41¹·²)x 1-e⁻°·°²⁽t⁻¹⁾}¹/¹·² over 1-e⁻⁽⁻°·°²⁾⁽¹³⁾ and for male fish. Age-at-50% maturity for females and males were estimated at 7 years and 4 years, respectively. Typically, fish grew rapidly in the first year, but slower during subsequent years. Smaller fish were found inshore while larger fish were found in offshore regions. It was hypothesised that the rapid growth in the first year and slower growth later is a consequence of change in diet from high quality and abundant food source to a more dilute food and that this may be associated with a shift in habitat. Morphological characters associated with feeding were used to predict the food and feeding behaviour of B. nyasensis. The size of premaxillary, vomerine, pharyngeal dental and palatine teeth and premaxillary and vomerine tooth plates suggested the capability of B. nyasensis to handle both large and small prey, with a propensity towards smaller prey in composition to C. gariepinus. The molariform teeth on the vomerine tooth plate suggested that molluscs form part of the diet. The relative gut length (1.27±0.24) suggested omnivory, with an ability to switch between planktivory and piscivory. Buccal cavity volume and filtering area changed with fish size at 500-600 mm TL upon which it was hypothesised that the fish diet changed to planktivory at this size. Detailed diet analysis provided information upon which the above hypotheses could be accepted. Percent Index of Relative Importance (%IRI) and a multi-way contingency table analysis based on log-linear models were used to analyse diet data. Results showed that B. nyasensis is omnivorous, but with a distinct ontogenetic dietary shift from piscivory to zooplanktivory at 500 - 600 mm TL. The increased buccal cavity volume at the same fish size therefore, suggests that B. nyasensis is well adapted to filter the dilute zooplankton resource. Increased foraging costs of feeding on zooplankton explained the slower growth of larger fish. The dietary shift was finally corroborated by results of the ∂¹³C isotope analysis. A polynomial equation described the change in carbon ratios with fish size: ∂¹³C = - 33.188 + 0.4997L - 0.0045 (total length)² (r² = 0.598, n = 12, p=0.022). The ontogenetic shift in diet was synchronised with a habitat shift postulated in life history studies. In the inshore region, B. nyasensis were predominantly piscivorous (apex predators), and were zooplanktivorous in the offshore region, thereby forming part of the pelagic food web in the latter region. After examining "bottom-up" and trophic cascade theories, it was postulated that perturbations of the B. nyasensis stock would be discernible both at the top and lower trophic levels. As a piscivore and therefore apex predator, effects of overfishing B. nyasensis in the inshore region could cascade to unpredictable ecological changes in inshore areas and, due to the ontogenetic habitat shift, in the offshore regions. Examples of trophic cascade phenomena are provided. On the basis of the feeding study, it was possible to reconstruct the pelagic food web of Lake Malawi. Apart from the lakefly Chaoborus edulis, B. nyasensis is the other predator that preys heavily on zooplankton in the pelagic zone. Perturbations of the B. nyasensis stock could affect size composition of zooplankton which in tum, could affect production of C. edulis, a resource for the top predators in the food web. The findings of the present study contributed to the ongoing debate of introducing a zooplanktivore into the pelagic zone of Lake Malawi. Proponents for the introductions have argued that zooplankton predation by fish is inferior to that of C. edulis. Introduction of a clupeid zooplankton was proposed as a strategy to boost fish production in the lake. The zooplanktivore would either out-compete or prey on C. edulis to extinction. Opponents to this view argued that zooplankton biomass in the pelagic region was too low to support introductions and that the fish biomass in the pelagic region may have been underestimated. Results from the present study suggest that planktivorous fish (including B. nyasensis) might not be inferior to C. edulis in utilising the zooplankton resource; B. nyasensis is well adapted to utilise the dilute zooplankton resource, and by omitting B. nyasensis from previous studies, overall zooplankton predation by fish may have been underestimated by between 7 - 33%. On the basis of the theoretical migratory life history cycle of B. nyasensis, it is recommended that the current interest in increasing fishing effort in offshore areas should proceed with caution. Ecological changes that may have occurred in the inshore areas due to overfishing have probably not been noticed: as the offshore zone has never been fished. The latter zone may have acted as a stock refuge area. Higher fishing intensity in the offshore areas could lead to serious ecological imbalances and instability. The study has shown that life history characteristics studied in the context of the food web, and in the absence of other fisheries information and/or data, strongly advocates the precautionary principle to managing changes in exploitation patterns.
- Full Text:
- Date Issued: 2001
Fish and fisheries of Bangweulu wetlands, Zambia
- Huchzermeyer, Carl Friedrich
- Authors: Huchzermeyer, Carl Friedrich
- Date: 2013
- Subjects: Bangweulu Swamps (Zambia) , Fisheries -- Zambia -- Bangweulu Swamps , Fishes -- Zambia -- Bangweulu Swamps , Fishery management -- Zambia -- Bangweulu Swamps , Fishing -- Zambia -- Bangweulu Swamps , Fishing -- Economic aspects -- Zambia -- Bangweulu Swamps , Fish stock assessment -- Zambia -- Bangweulu Swamps , Fish as food -- Zambia -- Bangweulu Swamps , Conservation of natural resources -- Zambia -- Bangweulu Swamps , Sustainable development -- Zambia -- Bangweulu Swamps
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5203 , http://hdl.handle.net/10962/d1003927 , Bangweulu Swamps (Zambia) , Fisheries -- Zambia -- Bangweulu Swamps , Fishes -- Zambia -- Bangweulu Swamps , Fishery management -- Zambia -- Bangweulu Swamps , Fishing -- Zambia -- Bangweulu Swamps , Fishing -- Economic aspects -- Zambia -- Bangweulu Swamps , Fish stock assessment -- Zambia -- Bangweulu Swamps , Fish as food -- Zambia -- Bangweulu Swamps , Conservation of natural resources -- Zambia -- Bangweulu Swamps , Sustainable development -- Zambia -- Bangweulu Swamps
- Description: Bangweulu Wetlands is a 6000 km² public-private-partnership conservation area in northeastern Zambia, lying on the south-eastern margins of the Bangweulu Swamps, Congo River system. The area is important for wildlife conservation, tourism and as a fishing ground for the local inhabitants. This study provides a baseline of the fish and fisheries of this area. The conservation area is situated on the transition zone between woodland, floodplain and swamp. A total of 42 fish species representing 12 taxonomic families were collected. The fish fauna of the area was characterised by a diversity of small cyprinids (14 species), cichlids (9 species), clariid catfishes (4 species) and mormyrids (4 species). Species such as Clarias gariepinus, C. ngamensis, Marcusenius macrolepidotus, Tilapia rendali, T. sparrmanii and several small Barbus species were shared with adjacent floodplain systems such as the upper Zambezi and Kafue rivers. Fishing was undertaken by fishing groups consisting of a fisherman and his family, or a group of men fishing together. Access to the fishing grounds was controlled by traditional fishing leaders, who collected tribute from fishermen. Fishing groups utilised fixed, distinct fishing areas determined by ancestry. The most important time for fishing was during the drawdown phase of the floodplains, from March until June. During the dry season fewer groups were engaged in fishing, with many having returned to farming activities. The main fishing methods of the floodplain fishery were basket traps and mosquito-mesh funnel nets set into earth fish barriers (fish weirs) constructed on the plains, various mesh sizes of gillnets, hook longlines and seine nets. The use of fish spears, drag baskets and piscicides was of lesser importance. Most fishing gears were constructed of a variety of natural and modern, manufactured materials. The fishery was multi-species and 23 fish species were recorded from in catch. The three most important species in the catches were C. gariepinus, T. rendalli and M. macrolepidotus. Together these contributed 67% by weight to the catch. Catch-per-unit-effort (CPUE) for the different gears was 0.4 ± 0.3 kg.trap.night⁻¹ for basket traps, 2.7 ± 4.6 kg.net.night⁻¹ for funnel nets, 0.3 ± 0.5 kg.50 m net.night⁻¹ for gill nets, 3.5 ± 6.3 kg.100 hooks.night⁻¹ for longlines, 1.79 ± 1.11 kg.haul⁻¹ for mosquito-mesh seine nets and 6.87 ± 6.27 kg.haul⁻¹ for larger-mesh seine nets. The weight of average daily landings of fishing groups, using a variety of gears was 7.8 ± 7.4 kg. Fishermen were able to maintain the same catch rate between dry and wet seasons, with no significant differences (p < 0.05) in daily landings between seasons. Yield per fisherman for a seven month season, which required 2-3 relocations due to falling water level, was 1.64 t based on catch assessment, and 1.9 t from a socio-economic survey. A tentative yield per area estimate for the area was 2I7 kg.ha⁻¹ over the three month shallow-floodplain fishing season. Most fish landed in the fishery were processed into sundried or smoke-dried products. These were used for 1) home consumption, 2) trade with village farmers (from up to 70 km inland of the fishing grounds) in exchange for staple starch meal, and 3) sold to urban fish traders, reaching markets as distant as Lubumbashi in Democratic Republic of Congo. Fish traders toured fishing camps to buy fish, supporting auxiliary industries such as transport and accommodation services. The price for dried fish at source was 3.14 ± 1.34 USDlkg and the market price reported for the Zambian Copperbelt was 6.14 ± 2.54 USD/kg. Typical returns on investment in fish trading were estimated as 68-77%. The fishery was considered to be biologically and socially sustainable. By harvesting a seasonally transient assemblage of species with high productivity and biological turnover rates and with life histories adapted to high mortality, fishermen were able to maintain a stable and viable livelihood. Management recommendations for the area were that a fisheries management plan be developed that would seek to strengthen the traditional system of rights-allocation, address problems between fishing and tourism activities, and enhance communication between fisheries and conservation stakeholders. To do this it was recommended that: 1) conservation authorities recognise the importance of the fishery, 2) no changes to current effort levels and fishing methods were necessary, 3) points 1 and 2 above be used to improve communication and trust between conservation authorities and fishermen, 4) customary resource-access mechanisms be understood and strengthened so that local inhabitants' rights to the resource are protected, 5) fishermen help formulate and accept conservation and tourism rules, 6) tourists and guides be made aware of the function of the fishery, 7) a fisheries management forum of key community, government and conservation stakeholders be formed to shape and implement the fisheries management plan, 8) locally-adapted bylaws be created to legitimise crucial floodplain gears currently considered illegal (e.g. mosquito-net gears, fish weirs), 9) no intervention to formalise fish trading be made, and 10) a trained person with a fisheries background be hired oversee the implementation of the recommendations.
- Full Text:
- Date Issued: 2013
- Authors: Huchzermeyer, Carl Friedrich
- Date: 2013
- Subjects: Bangweulu Swamps (Zambia) , Fisheries -- Zambia -- Bangweulu Swamps , Fishes -- Zambia -- Bangweulu Swamps , Fishery management -- Zambia -- Bangweulu Swamps , Fishing -- Zambia -- Bangweulu Swamps , Fishing -- Economic aspects -- Zambia -- Bangweulu Swamps , Fish stock assessment -- Zambia -- Bangweulu Swamps , Fish as food -- Zambia -- Bangweulu Swamps , Conservation of natural resources -- Zambia -- Bangweulu Swamps , Sustainable development -- Zambia -- Bangweulu Swamps
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5203 , http://hdl.handle.net/10962/d1003927 , Bangweulu Swamps (Zambia) , Fisheries -- Zambia -- Bangweulu Swamps , Fishes -- Zambia -- Bangweulu Swamps , Fishery management -- Zambia -- Bangweulu Swamps , Fishing -- Zambia -- Bangweulu Swamps , Fishing -- Economic aspects -- Zambia -- Bangweulu Swamps , Fish stock assessment -- Zambia -- Bangweulu Swamps , Fish as food -- Zambia -- Bangweulu Swamps , Conservation of natural resources -- Zambia -- Bangweulu Swamps , Sustainable development -- Zambia -- Bangweulu Swamps
- Description: Bangweulu Wetlands is a 6000 km² public-private-partnership conservation area in northeastern Zambia, lying on the south-eastern margins of the Bangweulu Swamps, Congo River system. The area is important for wildlife conservation, tourism and as a fishing ground for the local inhabitants. This study provides a baseline of the fish and fisheries of this area. The conservation area is situated on the transition zone between woodland, floodplain and swamp. A total of 42 fish species representing 12 taxonomic families were collected. The fish fauna of the area was characterised by a diversity of small cyprinids (14 species), cichlids (9 species), clariid catfishes (4 species) and mormyrids (4 species). Species such as Clarias gariepinus, C. ngamensis, Marcusenius macrolepidotus, Tilapia rendali, T. sparrmanii and several small Barbus species were shared with adjacent floodplain systems such as the upper Zambezi and Kafue rivers. Fishing was undertaken by fishing groups consisting of a fisherman and his family, or a group of men fishing together. Access to the fishing grounds was controlled by traditional fishing leaders, who collected tribute from fishermen. Fishing groups utilised fixed, distinct fishing areas determined by ancestry. The most important time for fishing was during the drawdown phase of the floodplains, from March until June. During the dry season fewer groups were engaged in fishing, with many having returned to farming activities. The main fishing methods of the floodplain fishery were basket traps and mosquito-mesh funnel nets set into earth fish barriers (fish weirs) constructed on the plains, various mesh sizes of gillnets, hook longlines and seine nets. The use of fish spears, drag baskets and piscicides was of lesser importance. Most fishing gears were constructed of a variety of natural and modern, manufactured materials. The fishery was multi-species and 23 fish species were recorded from in catch. The three most important species in the catches were C. gariepinus, T. rendalli and M. macrolepidotus. Together these contributed 67% by weight to the catch. Catch-per-unit-effort (CPUE) for the different gears was 0.4 ± 0.3 kg.trap.night⁻¹ for basket traps, 2.7 ± 4.6 kg.net.night⁻¹ for funnel nets, 0.3 ± 0.5 kg.50 m net.night⁻¹ for gill nets, 3.5 ± 6.3 kg.100 hooks.night⁻¹ for longlines, 1.79 ± 1.11 kg.haul⁻¹ for mosquito-mesh seine nets and 6.87 ± 6.27 kg.haul⁻¹ for larger-mesh seine nets. The weight of average daily landings of fishing groups, using a variety of gears was 7.8 ± 7.4 kg. Fishermen were able to maintain the same catch rate between dry and wet seasons, with no significant differences (p < 0.05) in daily landings between seasons. Yield per fisherman for a seven month season, which required 2-3 relocations due to falling water level, was 1.64 t based on catch assessment, and 1.9 t from a socio-economic survey. A tentative yield per area estimate for the area was 2I7 kg.ha⁻¹ over the three month shallow-floodplain fishing season. Most fish landed in the fishery were processed into sundried or smoke-dried products. These were used for 1) home consumption, 2) trade with village farmers (from up to 70 km inland of the fishing grounds) in exchange for staple starch meal, and 3) sold to urban fish traders, reaching markets as distant as Lubumbashi in Democratic Republic of Congo. Fish traders toured fishing camps to buy fish, supporting auxiliary industries such as transport and accommodation services. The price for dried fish at source was 3.14 ± 1.34 USDlkg and the market price reported for the Zambian Copperbelt was 6.14 ± 2.54 USD/kg. Typical returns on investment in fish trading were estimated as 68-77%. The fishery was considered to be biologically and socially sustainable. By harvesting a seasonally transient assemblage of species with high productivity and biological turnover rates and with life histories adapted to high mortality, fishermen were able to maintain a stable and viable livelihood. Management recommendations for the area were that a fisheries management plan be developed that would seek to strengthen the traditional system of rights-allocation, address problems between fishing and tourism activities, and enhance communication between fisheries and conservation stakeholders. To do this it was recommended that: 1) conservation authorities recognise the importance of the fishery, 2) no changes to current effort levels and fishing methods were necessary, 3) points 1 and 2 above be used to improve communication and trust between conservation authorities and fishermen, 4) customary resource-access mechanisms be understood and strengthened so that local inhabitants' rights to the resource are protected, 5) fishermen help formulate and accept conservation and tourism rules, 6) tourists and guides be made aware of the function of the fishery, 7) a fisheries management forum of key community, government and conservation stakeholders be formed to shape and implement the fisheries management plan, 8) locally-adapted bylaws be created to legitimise crucial floodplain gears currently considered illegal (e.g. mosquito-net gears, fish weirs), 9) no intervention to formalise fish trading be made, and 10) a trained person with a fisheries background be hired oversee the implementation of the recommendations.
- Full Text:
- Date Issued: 2013
Fish population dynamics in a temporarily open/closed South African estuary
- Cowley, Paul D (Paul Denfer), 1964-
- Authors: Cowley, Paul D (Paul Denfer), 1964-
- Date: 1999
- Subjects: Fish populations Estuarine ecology -- South Africa -- Eastern Cape Estuarine fishes -- Ecology -- South Africa Fish populations -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5354 , http://hdl.handle.net/10962/d1008543
- Description: The primary aim of this study was to investigate the population dynamics of the fishes associated with a small (17.5 hectares) temporarily open/closed estuary on the south east coast of South Africa. The results are based on the findings of an intensive sampling programme conducted over a period of four years in the East Kleinemonde estuary (33° 32' S : 27° 03' E). By adopting a quantitative approach, this study addresses the need for information on estuarine-associated fish population sizes, standing stock (biomass) estimates and productivity. The ichthyoplankton assemblage in the surf zone adjacent to the mouth of the estuary was dominated by postflexion larvae representing at least 21 taxa in 14 families. Rhabdosargus holubi of sizes ranging between 9 mm and 21 mm BL was the most abundant species with a mean density of 7.3 individuals per 100 m'. This species, which accounted for 77.6% of the catch composition, was recorded throughout the year but revealed a distinct peak in abundance in spring (August - September). The ichthyofaunal community within the East Kleinemonde estuary was dominated by juvenile marine-spawning species and typical of a warm temperate southern African estuary. A total of 30 species in 17 families was recorded, including the endangered estuarine pipefish Syngnathus watermeyeri. Multivariate analyses (classification and ordination) of the catch assemblages revealed a high degree of similarity (> 70%) throughout the estuary, with two distinct groups being identified on the basis of substratum type. The sampling stations near the mouth with a sandy substratum were distinguished from all other sampling sites in the estuary. The dominant estuarine-spawning species were represented by all life-history stages, suggesting that they bred successfully in the estuary. This group was numerically and gravimetrically dominated by the two zooplanktivorous shoaling species Gilchristella aestuaria and Atherina breviceps with density extrapolated population size estimates of 420 973 and 198 275 individuals, and biomass estimates of 1.6 and 0.6 g m⁻² respectively. The total population size of all estuarine-spawning species with a mean biomass 00.4 g m⁻² was estimated at 754 217 individuals. Population size estimates of the marine-spawning species were calculated using data obtained from three independent mark-recapture experiments. The assumptions for the mark-recapture analyses were adequately met and it was concluded that the techniques provided reliable estimates of population size. However, estimates obtained from density extrapolation revealed enormous variability and were considered to be unreliable. The total population size was estimated at 63 342, 18 592 and 13 5 192 during the three mark-recapture experiments respectively. The numerically dominant species during all three experiments was Rhabdosargus holubi. Biomass production of the marine-spawning species was evaluated over a 123 day census period when population sizes and estimates of growth rates were known. Productivity for all fishes with a standing stock of 26.2 g m⁻² was calculated at 4.5 g m⁻² month01 Rhabdosargus holubi accounted for more than 75% of the total marine fish productivity. This study draws attention to the success of Rhabdosargus holubi in the East Kleinemonde estuary, which is ascribed to aspects of its biology. These include an extended breeding season, the ability to recruit into the estuary under adverse open mouth conditions and its omnivorous food habits. The dominance of this migratory species suggests that it plays an important role in the transfer of energy to the coastal marine environment when the mouth of the East Kleinemonde estuary opens. Predation by birds and a dominant piscivorous fish (Lichia amia) was quantitatively assessed over a period of two years. Monthly food consumption by all piscivorous birds revealed large temporal variability, ranging from 32 to 466 kg month-I An unusual invasion of Cape cormorants during the winter of 1994 accounted for large scale mortality (2246 kg of fish) over a relatively short period. The predatory impact of this episodic event was reflected in the findings of the fish mark-recapture experiments, which revealed a 70% reduction in the total population of marine-spawning fishes (above a certain minimum size) in the estuary subsequent to this invasion. Monthly food consumption by the Lichia amia population in the estuary was calculated at 68 and 58 kg month-I for two distinct time periods when the population size was known. These findings suggest that this species is the top piscivorous predator in the East Kleinemonde estuary. Finally, the findings of this study highlight the temporal variability of fish populations within a single estuary. It is suggested that predation and estuary mouth conditions are the main factors influencing the abundance (and its variability) of individual species in the East Kleinemonde estuary.
- Full Text:
- Date Issued: 1999
- Authors: Cowley, Paul D (Paul Denfer), 1964-
- Date: 1999
- Subjects: Fish populations Estuarine ecology -- South Africa -- Eastern Cape Estuarine fishes -- Ecology -- South Africa Fish populations -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5354 , http://hdl.handle.net/10962/d1008543
- Description: The primary aim of this study was to investigate the population dynamics of the fishes associated with a small (17.5 hectares) temporarily open/closed estuary on the south east coast of South Africa. The results are based on the findings of an intensive sampling programme conducted over a period of four years in the East Kleinemonde estuary (33° 32' S : 27° 03' E). By adopting a quantitative approach, this study addresses the need for information on estuarine-associated fish population sizes, standing stock (biomass) estimates and productivity. The ichthyoplankton assemblage in the surf zone adjacent to the mouth of the estuary was dominated by postflexion larvae representing at least 21 taxa in 14 families. Rhabdosargus holubi of sizes ranging between 9 mm and 21 mm BL was the most abundant species with a mean density of 7.3 individuals per 100 m'. This species, which accounted for 77.6% of the catch composition, was recorded throughout the year but revealed a distinct peak in abundance in spring (August - September). The ichthyofaunal community within the East Kleinemonde estuary was dominated by juvenile marine-spawning species and typical of a warm temperate southern African estuary. A total of 30 species in 17 families was recorded, including the endangered estuarine pipefish Syngnathus watermeyeri. Multivariate analyses (classification and ordination) of the catch assemblages revealed a high degree of similarity (> 70%) throughout the estuary, with two distinct groups being identified on the basis of substratum type. The sampling stations near the mouth with a sandy substratum were distinguished from all other sampling sites in the estuary. The dominant estuarine-spawning species were represented by all life-history stages, suggesting that they bred successfully in the estuary. This group was numerically and gravimetrically dominated by the two zooplanktivorous shoaling species Gilchristella aestuaria and Atherina breviceps with density extrapolated population size estimates of 420 973 and 198 275 individuals, and biomass estimates of 1.6 and 0.6 g m⁻² respectively. The total population size of all estuarine-spawning species with a mean biomass 00.4 g m⁻² was estimated at 754 217 individuals. Population size estimates of the marine-spawning species were calculated using data obtained from three independent mark-recapture experiments. The assumptions for the mark-recapture analyses were adequately met and it was concluded that the techniques provided reliable estimates of population size. However, estimates obtained from density extrapolation revealed enormous variability and were considered to be unreliable. The total population size was estimated at 63 342, 18 592 and 13 5 192 during the three mark-recapture experiments respectively. The numerically dominant species during all three experiments was Rhabdosargus holubi. Biomass production of the marine-spawning species was evaluated over a 123 day census period when population sizes and estimates of growth rates were known. Productivity for all fishes with a standing stock of 26.2 g m⁻² was calculated at 4.5 g m⁻² month01 Rhabdosargus holubi accounted for more than 75% of the total marine fish productivity. This study draws attention to the success of Rhabdosargus holubi in the East Kleinemonde estuary, which is ascribed to aspects of its biology. These include an extended breeding season, the ability to recruit into the estuary under adverse open mouth conditions and its omnivorous food habits. The dominance of this migratory species suggests that it plays an important role in the transfer of energy to the coastal marine environment when the mouth of the East Kleinemonde estuary opens. Predation by birds and a dominant piscivorous fish (Lichia amia) was quantitatively assessed over a period of two years. Monthly food consumption by all piscivorous birds revealed large temporal variability, ranging from 32 to 466 kg month-I An unusual invasion of Cape cormorants during the winter of 1994 accounted for large scale mortality (2246 kg of fish) over a relatively short period. The predatory impact of this episodic event was reflected in the findings of the fish mark-recapture experiments, which revealed a 70% reduction in the total population of marine-spawning fishes (above a certain minimum size) in the estuary subsequent to this invasion. Monthly food consumption by the Lichia amia population in the estuary was calculated at 68 and 58 kg month-I for two distinct time periods when the population size was known. These findings suggest that this species is the top piscivorous predator in the East Kleinemonde estuary. Finally, the findings of this study highlight the temporal variability of fish populations within a single estuary. It is suggested that predation and estuary mouth conditions are the main factors influencing the abundance (and its variability) of individual species in the East Kleinemonde estuary.
- Full Text:
- Date Issued: 1999
Gametogenesis, gonadal recrudescence, restraint and spawning patterns in Nile perch, Lates niloticus (Linnaeus, 1758)
- Authors: Kahwa, David
- Date: 2013
- Subjects: Nile perch -- Victoria, Lake Gametogenesis Oogenesis Spermatogenesis Nile perch -- Spawning -- Victoria, Lake Nile perch -- Induced spawning -- Victoria, Lake Nile perch -- Reproduction -- Endocrine aspects -- Victoria, Lake Fish culture -- Victoria, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5182 , http://hdl.handle.net/10962/d1001834
- Description: The Nile perch, Lates niloticus (Linnaeus, 1758), is a predacious freshwater fish widely distributed throughout the Afro-tropic eco-zone. The species was introduced to Lake Victoria in the early 1950s and by 1980 it had dominated the fisheries of Lake Victoria. This was followed by a dramatic decrease in the Nile perch fisheries production due to uncontrolled exploitation. The purpose of this thesis is to provide fundamental knowledge that can be applied in aquaculture and fisheries management through the study of the reproductive biology of L. niloticus. The research was aimed at the studying of the diverse aspects of the reproductive biology of L. niloticus in the Lake Victoria, Ugandan populations. This included reproductive patterns in relation to proximate environmental conditions, size at sexual maturity, gonad and gamete structure, gametogenesis and induced ovulation. The size at 50% sexual maturity for female Nile perch was 59.4 cm, which is lower than the earlier reported size of greater than 90 cm total length. Male L. niloticus matured at 57.8 cm total length in Lake Victoria. Microscopy revealed that L. niloticus from Lake Victoria had one spawning period that started in November and ended in March. Type I atresia occurred at high frequency from March to June, and type III atresia was present from July to September and between November and December. Spermatogenesis in L. niloticus is cystic and sperm development is the result of asynchronous activation of the germ cells. Type II spermatozoa are simple, uni-flagellate aquasperm with no acrosome. Oogenesis in L. niloticus differed from that of other fishes in that no cortical alveoli were present in any stage of oogenesis. Numerous oil globules were present in the primary yolk vesicle stage. This formed one centrally positioned, large oil globule in the tertiary yolk vesicle oocytes during final oocyte maturation. Clove oil was an effective sedative and an anaesthetic for the handling of L. niloticus. Induction time was more rapid at clove oil concentrations of 50 - 100 μl L⁻¹ than in fish exposed to clove oil concentrations less than 50 μl L⁻¹. Fish exposed to high concentrations exhibited significantly short induction times of less than 240 seconds. On average, fish recovered within 673 ± 58 seconds for all the concentrations used. Prolonged exposure of L. niloticus to low clove oil concentrations of 2.5 - 10 μl L⁻¹ did not change the blood plasma cortisol, glucose, and the lactate and chloride ion concentration, relative to the control treatment. Captive breeding was attempted by conducting induced spawning experiments. Only final oocyte maturation was achieved using a decapeptide Gonadotropin Releasing Hormone (Dargin, sGnRH-MET), combined with a water-soluble dopamine receptor antagonist metoclopramide. This thesis suggests a research approach that provides a basis for aquaculture of the new species by first studying reproductive biology patterns and then linking the information to gonad and gamete structure so that spawning times can be estimated. It further provides insights into aspects of the reproductive biology of the species and the effects of hormonal intervention on oocytes by showing at which stage of oocyte development hormones should be applied in L. niloticus. Clove oil can be used to sedate and anaesthetise L. niloticus broodfish to reduce the stress related to the handling of large specimens.
- Full Text:
- Date Issued: 2013
- Authors: Kahwa, David
- Date: 2013
- Subjects: Nile perch -- Victoria, Lake Gametogenesis Oogenesis Spermatogenesis Nile perch -- Spawning -- Victoria, Lake Nile perch -- Induced spawning -- Victoria, Lake Nile perch -- Reproduction -- Endocrine aspects -- Victoria, Lake Fish culture -- Victoria, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5182 , http://hdl.handle.net/10962/d1001834
- Description: The Nile perch, Lates niloticus (Linnaeus, 1758), is a predacious freshwater fish widely distributed throughout the Afro-tropic eco-zone. The species was introduced to Lake Victoria in the early 1950s and by 1980 it had dominated the fisheries of Lake Victoria. This was followed by a dramatic decrease in the Nile perch fisheries production due to uncontrolled exploitation. The purpose of this thesis is to provide fundamental knowledge that can be applied in aquaculture and fisheries management through the study of the reproductive biology of L. niloticus. The research was aimed at the studying of the diverse aspects of the reproductive biology of L. niloticus in the Lake Victoria, Ugandan populations. This included reproductive patterns in relation to proximate environmental conditions, size at sexual maturity, gonad and gamete structure, gametogenesis and induced ovulation. The size at 50% sexual maturity for female Nile perch was 59.4 cm, which is lower than the earlier reported size of greater than 90 cm total length. Male L. niloticus matured at 57.8 cm total length in Lake Victoria. Microscopy revealed that L. niloticus from Lake Victoria had one spawning period that started in November and ended in March. Type I atresia occurred at high frequency from March to June, and type III atresia was present from July to September and between November and December. Spermatogenesis in L. niloticus is cystic and sperm development is the result of asynchronous activation of the germ cells. Type II spermatozoa are simple, uni-flagellate aquasperm with no acrosome. Oogenesis in L. niloticus differed from that of other fishes in that no cortical alveoli were present in any stage of oogenesis. Numerous oil globules were present in the primary yolk vesicle stage. This formed one centrally positioned, large oil globule in the tertiary yolk vesicle oocytes during final oocyte maturation. Clove oil was an effective sedative and an anaesthetic for the handling of L. niloticus. Induction time was more rapid at clove oil concentrations of 50 - 100 μl L⁻¹ than in fish exposed to clove oil concentrations less than 50 μl L⁻¹. Fish exposed to high concentrations exhibited significantly short induction times of less than 240 seconds. On average, fish recovered within 673 ± 58 seconds for all the concentrations used. Prolonged exposure of L. niloticus to low clove oil concentrations of 2.5 - 10 μl L⁻¹ did not change the blood plasma cortisol, glucose, and the lactate and chloride ion concentration, relative to the control treatment. Captive breeding was attempted by conducting induced spawning experiments. Only final oocyte maturation was achieved using a decapeptide Gonadotropin Releasing Hormone (Dargin, sGnRH-MET), combined with a water-soluble dopamine receptor antagonist metoclopramide. This thesis suggests a research approach that provides a basis for aquaculture of the new species by first studying reproductive biology patterns and then linking the information to gonad and gamete structure so that spawning times can be estimated. It further provides insights into aspects of the reproductive biology of the species and the effects of hormonal intervention on oocytes by showing at which stage of oocyte development hormones should be applied in L. niloticus. Clove oil can be used to sedate and anaesthetise L. niloticus broodfish to reduce the stress related to the handling of large specimens.
- Full Text:
- Date Issued: 2013
Genetic and morphometric variation of Octopus vulgaris in the Benguela Current region
- Authors: De Beer, Chénelle Lesley
- Date: 2014
- Subjects: Common octopus -- Africa, Southern , Common octopus -- Genetics , Common octopus -- Morphology , Common octopus -- Geographical distribution , Variation (Biology) , Benguela Current
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5362 , http://hdl.handle.net/10962/d1012971
- Description: The Benguela Current is a cold eastern boundary current located on the south-western coast of the African continent. The establishment of its present day features approximately two million years ago has triggered allopatric events which have driven genetic and/or phenotypic differentiation in many of the warm-temperate organisms that previously had continuous distributions along the south and west coast of southern Africa. However, since many of these species have responded differently, despite similar isolation times, research in this region provides a unique opportunity to increase our understanding of evolutionary processes. The common octopus (Octopus vulgaris, Cuvier 1797) is a coastal, sedentary species, inhabiting coral reefs or rocky environments at depths of up to a 100m. It is considered to be one of the most extensively studied cephalopod species due to its worldwide distribution. However, very little research has been conducted on O. vulgaris in southern Africa. In order to gain a holistic understanding of the effects of the Benguela Current on population connectivity, genetic and phenotypic diversity, and evolutionary history of O. vulgaris, a comparative genetic and morphological study was conducted across the Benguela region. A total of 168 specimens of O. vulgaris were collected from four different regions across the Benguela system. A small tissue sample was preserved in ethanol for molecular analysis, and the specimen was frozen whole for morphometric analysis in the laboratory. Octopus vulgaris genetic population structure and evolutionary history was investigated using a 580bp fragment of the mitochondrial cytochrome b (cytb) gene for 76 individuals located within the Benguela region, yielding 10 different haplotypes. AMOVA and pairwise FST analyses revealed significant genetic differentiation suggesting a northern-southern Benguela divergence. Estimates of time since most recent common ancestor, based on biogeographical calibrators and coalescent analyses, indicated that isolation between the Angolan and South African population occurred between ~231 Ka and 1 Ma. Mismatch distribution analyses revealed a past population expansion within the South African O. vulgaris roughly 129.31 Ka, whilst Bayesian skyline plots were indicative of gradual demographic growth within the Angolan population in the last ~100 Ka. Observed O. vulgaris population structure and demographic history was likely the result of historical climate-induced change within the system. Reconstruction of phylogenetic relationships within the Octopus genus, using cytb and COI suggest that O. vulgaris is not a monophyletic group and a major systematic revision is required. Furthermore, unidentified individuals from South Africa were found to group with species from Indo-West Pacific Oceans and were therefore considered to have been translocated through ballast water from Asia. While the molecular analysis indicated a significant northern-southern Benguela structure results from the principle component analysis (PCA) and discriminate function analysis (DFA) were unable to distinguish between O. vulgaris from different sampling localities throughout the Benguela Current region based on soft-parts, hard-parts and meristic characters. The lack of phenotypic variation, despite significant genetic divergence, highlights the importance of multi-method approaches in gaining a holistic understanding of the taxonomy and biogeography of species.
- Full Text:
- Date Issued: 2014
- Authors: De Beer, Chénelle Lesley
- Date: 2014
- Subjects: Common octopus -- Africa, Southern , Common octopus -- Genetics , Common octopus -- Morphology , Common octopus -- Geographical distribution , Variation (Biology) , Benguela Current
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5362 , http://hdl.handle.net/10962/d1012971
- Description: The Benguela Current is a cold eastern boundary current located on the south-western coast of the African continent. The establishment of its present day features approximately two million years ago has triggered allopatric events which have driven genetic and/or phenotypic differentiation in many of the warm-temperate organisms that previously had continuous distributions along the south and west coast of southern Africa. However, since many of these species have responded differently, despite similar isolation times, research in this region provides a unique opportunity to increase our understanding of evolutionary processes. The common octopus (Octopus vulgaris, Cuvier 1797) is a coastal, sedentary species, inhabiting coral reefs or rocky environments at depths of up to a 100m. It is considered to be one of the most extensively studied cephalopod species due to its worldwide distribution. However, very little research has been conducted on O. vulgaris in southern Africa. In order to gain a holistic understanding of the effects of the Benguela Current on population connectivity, genetic and phenotypic diversity, and evolutionary history of O. vulgaris, a comparative genetic and morphological study was conducted across the Benguela region. A total of 168 specimens of O. vulgaris were collected from four different regions across the Benguela system. A small tissue sample was preserved in ethanol for molecular analysis, and the specimen was frozen whole for morphometric analysis in the laboratory. Octopus vulgaris genetic population structure and evolutionary history was investigated using a 580bp fragment of the mitochondrial cytochrome b (cytb) gene for 76 individuals located within the Benguela region, yielding 10 different haplotypes. AMOVA and pairwise FST analyses revealed significant genetic differentiation suggesting a northern-southern Benguela divergence. Estimates of time since most recent common ancestor, based on biogeographical calibrators and coalescent analyses, indicated that isolation between the Angolan and South African population occurred between ~231 Ka and 1 Ma. Mismatch distribution analyses revealed a past population expansion within the South African O. vulgaris roughly 129.31 Ka, whilst Bayesian skyline plots were indicative of gradual demographic growth within the Angolan population in the last ~100 Ka. Observed O. vulgaris population structure and demographic history was likely the result of historical climate-induced change within the system. Reconstruction of phylogenetic relationships within the Octopus genus, using cytb and COI suggest that O. vulgaris is not a monophyletic group and a major systematic revision is required. Furthermore, unidentified individuals from South Africa were found to group with species from Indo-West Pacific Oceans and were therefore considered to have been translocated through ballast water from Asia. While the molecular analysis indicated a significant northern-southern Benguela structure results from the principle component analysis (PCA) and discriminate function analysis (DFA) were unable to distinguish between O. vulgaris from different sampling localities throughout the Benguela Current region based on soft-parts, hard-parts and meristic characters. The lack of phenotypic variation, despite significant genetic divergence, highlights the importance of multi-method approaches in gaining a holistic understanding of the taxonomy and biogeography of species.
- Full Text:
- Date Issued: 2014
Genetic diversity, evolutionary relationships and conservation of southern African Labeo fishes in relation to water management
- Authors: Ramoejane, Mpho
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5209 , vital:20786
- Description: Labeo spp. are large, herbivorous fishes that are important components of aquatic ecosystems and are a high conservation priority in South Africa. This thesis contributes to determination of conservation priorities for Labeo umbratus (Smith 1841) by resolving the taxonomic status of this species in the evolutionary context of southern African Labeo spp., assessing the presence of unique lineages in historically isolated river basins, and assessing the threat of intra- and interspecific hybridisation associated with introductions. Phylogenetic analyses of five DNA sequence data sets (cytochrome c oxidase subunit I gene [COI], cytochrome b gene [Cyt b], Recombination activating gene 1 [Rag1], COI+Rag1 and COI+Cyt b+Rag1) showed that the Labeo umbratus group (sensu Reid, 1985), which comprises the species Labeo umbratus, Labeo capensis (Smith 1841), Labeo seeberi Gilchrist and Thompson 1911 and Labeo rubromaculatus Gilchrist and Thompson 1913, is monophyletic, morphologically distinct and geographically disjunct from other African Labeo spp. groups except in the Tugela River system were L. rubromaculatus co-occurs with Labeo molybdinus Du Plessis 1963. Phylogeographic analysis of mitochondrial DNA (Cyt b) sequence data demonstrated that the populations of the L. umbratus from the Orange and the southward-flowing river systems are reciprocally monophyletic and were identified as evolutionary significant units. The populations in the southward-flowing river systems were further divided into southwestern (Gourits and Gamtoos) and southeastern (Sundays, Bushmans, Great Fish, Keiskamma, Buffalo and Nahoon) polyp hyletic sublineages. Four management units (Gourits Basin; Gamtoos Basin; Sundays+Bushmans+Great Fish River Basins; and Keiskamma+Buffalo+Nahoon River Basin) were not reciprocally monophyletic but were proposed on the basis of containing unique haplotype frequencies for conservation purposes. To evaluate the threat of hybridisation to the genetic integrity of L. umbratus, the occurrence of Labeo umbratus x L. capensis hybrids was investigated using mtDNA Cyt b and nDNA S7 intron sequence data and morphological data. Genetic evidence for interspecific hybridisation was detected for populations in two impoundments, Hardap Dam (Orange River Basin) and Darlington Dam (Sundays River Basin, Eastern Cape, South Africa). Some putative hybrids were identifiable morphologically on account of intermediacy between the parental species in meristic and morphometric characters. Translocation via direct stocking (Hardap Dam) or via an inter-basin water transfer scheme (Darlington Dam) was identified as a driver for hybridisation. Introductions associated with an inter-basin water transfer scheme has resulted in introgression between the previously isolated Orange River and southern lineages of L. umbratus. Further translocation of fish from these affected areas to non-contaminated river systems and impoundments such as Kat River (Great Fish River) and Slagboom (Sundays River) should be avoided.
- Full Text:
- Date Issued: 2017
- Authors: Ramoejane, Mpho
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5209 , vital:20786
- Description: Labeo spp. are large, herbivorous fishes that are important components of aquatic ecosystems and are a high conservation priority in South Africa. This thesis contributes to determination of conservation priorities for Labeo umbratus (Smith 1841) by resolving the taxonomic status of this species in the evolutionary context of southern African Labeo spp., assessing the presence of unique lineages in historically isolated river basins, and assessing the threat of intra- and interspecific hybridisation associated with introductions. Phylogenetic analyses of five DNA sequence data sets (cytochrome c oxidase subunit I gene [COI], cytochrome b gene [Cyt b], Recombination activating gene 1 [Rag1], COI+Rag1 and COI+Cyt b+Rag1) showed that the Labeo umbratus group (sensu Reid, 1985), which comprises the species Labeo umbratus, Labeo capensis (Smith 1841), Labeo seeberi Gilchrist and Thompson 1911 and Labeo rubromaculatus Gilchrist and Thompson 1913, is monophyletic, morphologically distinct and geographically disjunct from other African Labeo spp. groups except in the Tugela River system were L. rubromaculatus co-occurs with Labeo molybdinus Du Plessis 1963. Phylogeographic analysis of mitochondrial DNA (Cyt b) sequence data demonstrated that the populations of the L. umbratus from the Orange and the southward-flowing river systems are reciprocally monophyletic and were identified as evolutionary significant units. The populations in the southward-flowing river systems were further divided into southwestern (Gourits and Gamtoos) and southeastern (Sundays, Bushmans, Great Fish, Keiskamma, Buffalo and Nahoon) polyp hyletic sublineages. Four management units (Gourits Basin; Gamtoos Basin; Sundays+Bushmans+Great Fish River Basins; and Keiskamma+Buffalo+Nahoon River Basin) were not reciprocally monophyletic but were proposed on the basis of containing unique haplotype frequencies for conservation purposes. To evaluate the threat of hybridisation to the genetic integrity of L. umbratus, the occurrence of Labeo umbratus x L. capensis hybrids was investigated using mtDNA Cyt b and nDNA S7 intron sequence data and morphological data. Genetic evidence for interspecific hybridisation was detected for populations in two impoundments, Hardap Dam (Orange River Basin) and Darlington Dam (Sundays River Basin, Eastern Cape, South Africa). Some putative hybrids were identifiable morphologically on account of intermediacy between the parental species in meristic and morphometric characters. Translocation via direct stocking (Hardap Dam) or via an inter-basin water transfer scheme (Darlington Dam) was identified as a driver for hybridisation. Introductions associated with an inter-basin water transfer scheme has resulted in introgression between the previously isolated Orange River and southern lineages of L. umbratus. Further translocation of fish from these affected areas to non-contaminated river systems and impoundments such as Kat River (Great Fish River) and Slagboom (Sundays River) should be avoided.
- Full Text:
- Date Issued: 2017
Genetic structure and biogeography of three wrasse species (Labridae) within the Western Indian Ocean
- Authors: Mayekiso, Sisanda
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1114 , vital:20021
- Description: The biogeography of wrasses within the Western Indian Ocean (WIO) is poorly understood, with regard to origins and genetic differentiation or connectivity among the regions of the WIO. This region is a good model for studying the influence of physical complexities and biogeographic breaks in shaping patterns of differentiation in wrasses. Three reef-associated fish species, Cheilio inermis, Thalassoma hebraicum and T. lunare, were selected to examine the factors that have influenced patterns of differentiation across the WIO. Each species was sampled from various localities of the WIO, the Red Sea and Indo-West Pacific Islands. Sequence data were generated from two mitochondrial gene fragments (cytochrome b and ATPase 6) and one nuclear locus (the first intron of the ribosomal protein S7 gene). Genetic analyses were used to calculate genetic diversity indices within species, which were then compared among species. The relationships among haplotypes and alleles were constructed using median-joining networks. Where necessary, neighbour-joining trees (NJ) were constructed to examine relationships among haplotypes and alleles for the Thalassoma species. Population structure was analysed using AMOVA and pairwise ФST to compare and calculate differentiation between the WIO localities. Mismatch distributions were used to examine population growth and decline or stability, and demographic parameters were used to calculate time of population expansion. There was high haplotype (h = 0.88 to 0.98) and low nucleotide diversities (π = 0.003 to 0.008) among all species for mitochondrial markers. For S7 intron I, high allelic (A = 0.95 to 0.98) and low nucleotide diversities (π = 0.002 to 0.014) were observed for all species. The pairwise ФST values revealed little to great (ФST = -0.02 to 0.67) genetic differentiation between localities, across all species for the three gene regions. The pairwise comparisons indicated the differentiation in C. inermis of Tanzania and Kenya from Mozambique and Nosy Be (Madagascar). The widespread C. inermis also revealed the differentiation of Kenya and Tanzania. For C. inermis, the AMOVAs of ATPase 6 and cytochrome b data indicated high differentiation among defined locality groups. The groups were defined according to geographic proximity. However, the AMOVA of the nuclear gene (S7 intron I) did not find variation among defined locality groups. Cheilio inermis revealed a sequence divergence of 0.4%. The divergence that was found in C. inermis was not enough to suggest a cryptic species within the WIO. Overall, the widespread and monotypic C. inermis revealed genetic differentiation within the WIO. Thalassoma hebraicum generally revealed little genetic differentiation across the WIO. The AMOVAs of the three gene regions showed no variation among specimens of the defined locality groups. However, some differentiation was found between localities. The pairwise comparisons of T. hebraicum revealed the differentiation of Seychelles from the African mainland and Madagascar. Southern Africa was observed to be differentiated from Nosy Be and Zanzibar. The observed differentiation could be caused by oceanic barriers such as the South Equatorial Current (SEQC), East African Coastal Current (EACC), and the Comoros Gyres and eddies in the Mozambique Channel, and Agulhas Current. Thalassoma lunare revealed genetic isolation between the WIO and the Red Sea as well as within the WIO. The genetic isolation between the WIO and the Red Sea is probably due to the historical isolation by the Bab al Mandab and contemporary barriers such as the cold upwelling cells in Somalia. The differentiation of Maldives from the African mainland and Seychelles could be due to distance and the upwelling cells created by monsoon winds. Mismatch distributions suggested that C. inermis and T. hebraicum had undergone demographic expansion during the Pleistocene (92 678 to 40 219 years ago). The results of the current study are similar to those from previous studies of WIO reef fish species, and the results of the present study could have potential implications for conservation and fisheries management. Single genetic markers and single species studies do not detect all barriers to dispersal in the WIO, thus they are insufficient to inform conservation management. Thus, the use of multispecies and genetic markers in the current study can be adopted by other studies of the marine taxa of the WIO.
- Full Text:
- Date Issued: 2016
- Authors: Mayekiso, Sisanda
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1114 , vital:20021
- Description: The biogeography of wrasses within the Western Indian Ocean (WIO) is poorly understood, with regard to origins and genetic differentiation or connectivity among the regions of the WIO. This region is a good model for studying the influence of physical complexities and biogeographic breaks in shaping patterns of differentiation in wrasses. Three reef-associated fish species, Cheilio inermis, Thalassoma hebraicum and T. lunare, were selected to examine the factors that have influenced patterns of differentiation across the WIO. Each species was sampled from various localities of the WIO, the Red Sea and Indo-West Pacific Islands. Sequence data were generated from two mitochondrial gene fragments (cytochrome b and ATPase 6) and one nuclear locus (the first intron of the ribosomal protein S7 gene). Genetic analyses were used to calculate genetic diversity indices within species, which were then compared among species. The relationships among haplotypes and alleles were constructed using median-joining networks. Where necessary, neighbour-joining trees (NJ) were constructed to examine relationships among haplotypes and alleles for the Thalassoma species. Population structure was analysed using AMOVA and pairwise ФST to compare and calculate differentiation between the WIO localities. Mismatch distributions were used to examine population growth and decline or stability, and demographic parameters were used to calculate time of population expansion. There was high haplotype (h = 0.88 to 0.98) and low nucleotide diversities (π = 0.003 to 0.008) among all species for mitochondrial markers. For S7 intron I, high allelic (A = 0.95 to 0.98) and low nucleotide diversities (π = 0.002 to 0.014) were observed for all species. The pairwise ФST values revealed little to great (ФST = -0.02 to 0.67) genetic differentiation between localities, across all species for the three gene regions. The pairwise comparisons indicated the differentiation in C. inermis of Tanzania and Kenya from Mozambique and Nosy Be (Madagascar). The widespread C. inermis also revealed the differentiation of Kenya and Tanzania. For C. inermis, the AMOVAs of ATPase 6 and cytochrome b data indicated high differentiation among defined locality groups. The groups were defined according to geographic proximity. However, the AMOVA of the nuclear gene (S7 intron I) did not find variation among defined locality groups. Cheilio inermis revealed a sequence divergence of 0.4%. The divergence that was found in C. inermis was not enough to suggest a cryptic species within the WIO. Overall, the widespread and monotypic C. inermis revealed genetic differentiation within the WIO. Thalassoma hebraicum generally revealed little genetic differentiation across the WIO. The AMOVAs of the three gene regions showed no variation among specimens of the defined locality groups. However, some differentiation was found between localities. The pairwise comparisons of T. hebraicum revealed the differentiation of Seychelles from the African mainland and Madagascar. Southern Africa was observed to be differentiated from Nosy Be and Zanzibar. The observed differentiation could be caused by oceanic barriers such as the South Equatorial Current (SEQC), East African Coastal Current (EACC), and the Comoros Gyres and eddies in the Mozambique Channel, and Agulhas Current. Thalassoma lunare revealed genetic isolation between the WIO and the Red Sea as well as within the WIO. The genetic isolation between the WIO and the Red Sea is probably due to the historical isolation by the Bab al Mandab and contemporary barriers such as the cold upwelling cells in Somalia. The differentiation of Maldives from the African mainland and Seychelles could be due to distance and the upwelling cells created by monsoon winds. Mismatch distributions suggested that C. inermis and T. hebraicum had undergone demographic expansion during the Pleistocene (92 678 to 40 219 years ago). The results of the current study are similar to those from previous studies of WIO reef fish species, and the results of the present study could have potential implications for conservation and fisheries management. Single genetic markers and single species studies do not detect all barriers to dispersal in the WIO, thus they are insufficient to inform conservation management. Thus, the use of multispecies and genetic markers in the current study can be adopted by other studies of the marine taxa of the WIO.
- Full Text:
- Date Issued: 2016
Growth and gonad size in cultured South African abalone, Haliotis midae
- Authors: Riddin, Nicholas Alwyn
- Date: 2013
- Subjects: Haliotis midae -- South Africa , Haliotis midae fisheries -- South Africa , Abalone culture -- South Africa , Abalones -- Physiology -- South Africa , Abalones -- Growth -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5180 , http://hdl.handle.net/10962/d1001651 , Haliotis midae -- South Africa , Haliotis midae fisheries -- South Africa , Abalone culture -- South Africa , Abalones -- Physiology -- South Africa , Abalones -- Growth -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Description: According to farm records, cultured Haliotis midae (50-70 g.abalone⁻¹) were growing 10% slower in winter when compared to summer. This reduction in growth rate also coincided with enlarged gonads. Initial trials showed that there were differences in mean monthly growth rates ranging from 1.97 – 5.14 g abalone⁻¹ month⁻¹, and gonad bulk index (GBI) also varied between months (GBI range: 26.88 ± 12.87 to 51.03 ± 34.47). The investment of energy into gonad tissue growth did not compromise whole body growth as the abalone continued to gain weight throughout the reproductive periods, probably due to gonadal growth. Growth of this size class of abalone was not influenced by water temperature or day length, suggesting favourable on-farm culture conditions (regression analyses, p > 0.05). There is no need to implement a seasonal dietary regime. Cultured H. midae were fed artificial diets with different protein sources, including only soya, only fishmeal, a combination of soya and fishmeal, and these were compared to kelp-fed abalone. Kelp-fed abalone grew slower than those fed artificial feeds (p>0.05). Gonad growth was the greatest when soya meal was included in the diet (average GBI: 74.91 ± 23.31), while the average gonad size of abalone fed the fishmealbased diet had gonads which were 38% smaller, and kelp-fed abalone had gonads which were 75% smaller than those of the abalone fed on diets containing soya meal. The increased gonad mass in abalone fed on diets including soya meal could be attributed to phytoestrogenic activity, as a result of the presence of isoflavones found in the soya plant; this remains to be tested. The use of soya in brood stock diet development is advised. The influence of dietary protein to energy ratio (1.41 – 2.46 g MJ⁻¹) on growth and gonad size was tested. Protein and energy levels within the ranges tested (22 and 33% protein; 13.5 and 15.6 MJ kg⁻¹) did not interact to influence growth rates of cultured H. midae. GBI increased from 50.67 ± 4.16 to 83.93 ± 9.35 units as a function of dietary protein to energy ratio (y = 42.02 x⁰·⁸¹; r² = 0.19; regression analysis: F₁¸₃₈ = 8.9; p = 0.005). In addition, protein level influenced gonad size, with gonad growth being greater in abalone fed the high protein diet (factorial ANOVA: F₁¸₃₂ = 7.1, p = 0.012). Canning yields were reduced by 7% when the protein content was increased, while increasing the quantity of dietary energy improved canning yields by ~ 6% (one-way ANOVA: F₁¸₂₈ = 14.4, p= 0.001). The present study provided evidence that although growth rates are varying seasonally, reproductive investment is not hindering weight gain. Gonad growth can be influenced if desired by farms, depending on the level of soya inclusion, as well as the protein to energy ratio in the diet. Monthly variation in growth and gonad size, as well as the influence of diet on gonad growth were highlighted, and the implications for farm application and further research were discussed.
- Full Text:
- Date Issued: 2013
- Authors: Riddin, Nicholas Alwyn
- Date: 2013
- Subjects: Haliotis midae -- South Africa , Haliotis midae fisheries -- South Africa , Abalone culture -- South Africa , Abalones -- Physiology -- South Africa , Abalones -- Growth -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5180 , http://hdl.handle.net/10962/d1001651 , Haliotis midae -- South Africa , Haliotis midae fisheries -- South Africa , Abalone culture -- South Africa , Abalones -- Physiology -- South Africa , Abalones -- Growth -- South Africa , Abalones -- Feeding and feeds -- South Africa
- Description: According to farm records, cultured Haliotis midae (50-70 g.abalone⁻¹) were growing 10% slower in winter when compared to summer. This reduction in growth rate also coincided with enlarged gonads. Initial trials showed that there were differences in mean monthly growth rates ranging from 1.97 – 5.14 g abalone⁻¹ month⁻¹, and gonad bulk index (GBI) also varied between months (GBI range: 26.88 ± 12.87 to 51.03 ± 34.47). The investment of energy into gonad tissue growth did not compromise whole body growth as the abalone continued to gain weight throughout the reproductive periods, probably due to gonadal growth. Growth of this size class of abalone was not influenced by water temperature or day length, suggesting favourable on-farm culture conditions (regression analyses, p > 0.05). There is no need to implement a seasonal dietary regime. Cultured H. midae were fed artificial diets with different protein sources, including only soya, only fishmeal, a combination of soya and fishmeal, and these were compared to kelp-fed abalone. Kelp-fed abalone grew slower than those fed artificial feeds (p>0.05). Gonad growth was the greatest when soya meal was included in the diet (average GBI: 74.91 ± 23.31), while the average gonad size of abalone fed the fishmealbased diet had gonads which were 38% smaller, and kelp-fed abalone had gonads which were 75% smaller than those of the abalone fed on diets containing soya meal. The increased gonad mass in abalone fed on diets including soya meal could be attributed to phytoestrogenic activity, as a result of the presence of isoflavones found in the soya plant; this remains to be tested. The use of soya in brood stock diet development is advised. The influence of dietary protein to energy ratio (1.41 – 2.46 g MJ⁻¹) on growth and gonad size was tested. Protein and energy levels within the ranges tested (22 and 33% protein; 13.5 and 15.6 MJ kg⁻¹) did not interact to influence growth rates of cultured H. midae. GBI increased from 50.67 ± 4.16 to 83.93 ± 9.35 units as a function of dietary protein to energy ratio (y = 42.02 x⁰·⁸¹; r² = 0.19; regression analysis: F₁¸₃₈ = 8.9; p = 0.005). In addition, protein level influenced gonad size, with gonad growth being greater in abalone fed the high protein diet (factorial ANOVA: F₁¸₃₂ = 7.1, p = 0.012). Canning yields were reduced by 7% when the protein content was increased, while increasing the quantity of dietary energy improved canning yields by ~ 6% (one-way ANOVA: F₁¸₂₈ = 14.4, p= 0.001). The present study provided evidence that although growth rates are varying seasonally, reproductive investment is not hindering weight gain. Gonad growth can be influenced if desired by farms, depending on the level of soya inclusion, as well as the protein to energy ratio in the diet. Monthly variation in growth and gonad size, as well as the influence of diet on gonad growth were highlighted, and the implications for farm application and further research were discussed.
- Full Text:
- Date Issued: 2013
Home range dynamics of spotted grunter, pomadasys commersonnii, in a South African intermittently open estuary
- Authors: O'Connell, Bronwyn Anne
- Date: 2008
- Subjects: Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5286 , http://hdl.handle.net/10962/d1005130 , Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Description: The spotted grunter (Pomadasys commersonnii) is an important, estuarine-dependent, fishery species in southern Africa. Since estuaries are essential habitats in the life history of this species, the quantification of area use patterns and movements is important for fisheries management. In this study, acoustic telemetry was used to investigate movements, use of habitat and home range dynamics of spotted grunter in the small intermittently open East Kleinemonde Estuary on the Eastern Cape coast of South Africa. Nine spotted grunter (range: 326-489mm TL) were surgically equipped with uniquely coded acoustic transmitters. Positional fixes were obtained by manual tracking tagged individuals on six days and six nights during five tracking sessions from March to November 2004. In addition, five stationary data-logging receivers, moored at specific locations from the mouth to the top of the estuary provided additional long-term monitoring. Kernel home ranges (95% UD) varied in size (26 296-165 321m²) but were all located in a common high use area situated between 300-1 300m from the estuary mouth, which coincided with the highest abundance of prey items. There was no significant variation in home range size [C² (N = 9, df = 4) = 4.18; p = 0.38] between the temporally segregated tracking sessions (over nine months). The persistence of these home range estimates were confirmed by the long-term data-logging receivers. There was no significant diel variation in home range size [F(4, 64) = 0.05, p = 0.99] or core area size [F(4, 64) = 1.40, p = 0.25]. Fish length showed negative, although not significant, relationships between home range size (p = 0.225); number of home range areas (p = 0.065); core area size (p = 0.512) and home range length (p = 0.320). Use of habitat and home range dynamics of spotted grunter in the East Kleinemonde Estuary were consistent over the nine month study period, and they appeared to be influenced more by biotic than abiotic factors. However, when the mouth opened at the end of the study, most tagged fish vacated their home ranges and emigrated to sea.
- Full Text:
- Date Issued: 2008
- Authors: O'Connell, Bronwyn Anne
- Date: 2008
- Subjects: Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5286 , http://hdl.handle.net/10962/d1005130 , Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Description: The spotted grunter (Pomadasys commersonnii) is an important, estuarine-dependent, fishery species in southern Africa. Since estuaries are essential habitats in the life history of this species, the quantification of area use patterns and movements is important for fisheries management. In this study, acoustic telemetry was used to investigate movements, use of habitat and home range dynamics of spotted grunter in the small intermittently open East Kleinemonde Estuary on the Eastern Cape coast of South Africa. Nine spotted grunter (range: 326-489mm TL) were surgically equipped with uniquely coded acoustic transmitters. Positional fixes were obtained by manual tracking tagged individuals on six days and six nights during five tracking sessions from March to November 2004. In addition, five stationary data-logging receivers, moored at specific locations from the mouth to the top of the estuary provided additional long-term monitoring. Kernel home ranges (95% UD) varied in size (26 296-165 321m²) but were all located in a common high use area situated between 300-1 300m from the estuary mouth, which coincided with the highest abundance of prey items. There was no significant variation in home range size [C² (N = 9, df = 4) = 4.18; p = 0.38] between the temporally segregated tracking sessions (over nine months). The persistence of these home range estimates were confirmed by the long-term data-logging receivers. There was no significant diel variation in home range size [F(4, 64) = 0.05, p = 0.99] or core area size [F(4, 64) = 1.40, p = 0.25]. Fish length showed negative, although not significant, relationships between home range size (p = 0.225); number of home range areas (p = 0.065); core area size (p = 0.512) and home range length (p = 0.320). Use of habitat and home range dynamics of spotted grunter in the East Kleinemonde Estuary were consistent over the nine month study period, and they appeared to be influenced more by biotic than abiotic factors. However, when the mouth opened at the end of the study, most tagged fish vacated their home ranges and emigrated to sea.
- Full Text:
- Date Issued: 2008
Ichthyofaunal community structures in different types of Eastern Cape estuaries
- Authors: Vorwerk, Paul D
- Date: 2001
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5377 , http://hdl.handle.net/10962/d1016241
- Description: This investigation had three major objectives; firstly to document the estuarine fishes from several poorly studied Eastern Cape estuaries, secondly, to identify similarities and differences in the fish communities from permanently open and intermittently open estuaries, and thirdly, to establish which physico-chemical or environmental variables are responsible for the structuring of these communities. The study area incorporated 10 estuaries along a 70 km long stretch of the Eastern Cape coastline between the towns of Seafield (33° 32' 42" S, 27° 03' 05" E) in the south-east and Hamburg (33° 16' 45" S, 27° 29' 50" E) in the north-west. The systems investigated included two permanently open estuaries and eight intermittently open systems of varying sizes. Overall fish abundance and species richness in the study area revealed no significant seasonal variation. A contrast between open and closed estuaries was evident in the dominance of species from different estuarine dependence categories. Open estuaries comprised mainly category Ib, lla and IIb species, with a high proportion of category IV species. Closed estuaries were dominated by category IIa species, with few category IV species represented. Clear longitudinal trends in relative abundance were demonstrated for individual species. Margalefs species richness index for seine net catches, and a combination of the seine and gill net data, were significantly correlated with catchment size, mean annual runoff, estuarine area and linear length. Fish assemblages in the permanently open and intermittently open estuaries were significantly different (p<0.001) when analysed on a community and density basis. Similarly, the communities in large and small intermittently open estuaries differed significantly on a community (p=0.01) and density basis (p<0.001). These differences where caused by changes in abundance of the dominant estuarine resident and marine migrant species. The environmental variable that was dominant in accounting for these differences was the estuary mouth status. Estuarine resident species had smaller overall body lengths when compared with the marine migrant species. In addition, the estuarine resident species had smaller modal size classes in the closed estuaries when compared with the open estuaries. These differences may be linked to the foraging strategies of the species, as well as food availability and different levels of predation in the different estuary types. The marine migrant species did not show any trends in this respect although the closed systems had the largest individuals for all four dominant marine species. This finding may be linked to the inability of these species to breed in closed estuaries, thus channelling reproductive energy resources into somatic growth. In addition, prolonged periods of mouth closure prevent the emigration of large individuals back to the sea. Otter trawling was conducted in fiye estuaries and captured mostly demersal species. The otter trawl data confirmed the seine net community analysis, with significantly different communities identified in the permanently open and intermittently open estuaries (p=0.02), as well as in the small and large intermittently open estuaries (p=0.03). The environmental variables responsible for these community differences were mouth status and variables associated with estuarine size. The identification of estuary mouth status by this study as the most influential environmental factor is compounded by this "ariable affecting or being indicative of numerous other physico-chemical features. The large differences in the fish communities in different estuary types indicate the importance of each estuary type to various species. This should be taken into account before allowing any form of commercial fishing in these important nursery areas.
- Full Text:
- Date Issued: 2001
- Authors: Vorwerk, Paul D
- Date: 2001
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5377 , http://hdl.handle.net/10962/d1016241
- Description: This investigation had three major objectives; firstly to document the estuarine fishes from several poorly studied Eastern Cape estuaries, secondly, to identify similarities and differences in the fish communities from permanently open and intermittently open estuaries, and thirdly, to establish which physico-chemical or environmental variables are responsible for the structuring of these communities. The study area incorporated 10 estuaries along a 70 km long stretch of the Eastern Cape coastline between the towns of Seafield (33° 32' 42" S, 27° 03' 05" E) in the south-east and Hamburg (33° 16' 45" S, 27° 29' 50" E) in the north-west. The systems investigated included two permanently open estuaries and eight intermittently open systems of varying sizes. Overall fish abundance and species richness in the study area revealed no significant seasonal variation. A contrast between open and closed estuaries was evident in the dominance of species from different estuarine dependence categories. Open estuaries comprised mainly category Ib, lla and IIb species, with a high proportion of category IV species. Closed estuaries were dominated by category IIa species, with few category IV species represented. Clear longitudinal trends in relative abundance were demonstrated for individual species. Margalefs species richness index for seine net catches, and a combination of the seine and gill net data, were significantly correlated with catchment size, mean annual runoff, estuarine area and linear length. Fish assemblages in the permanently open and intermittently open estuaries were significantly different (p<0.001) when analysed on a community and density basis. Similarly, the communities in large and small intermittently open estuaries differed significantly on a community (p=0.01) and density basis (p<0.001). These differences where caused by changes in abundance of the dominant estuarine resident and marine migrant species. The environmental variable that was dominant in accounting for these differences was the estuary mouth status. Estuarine resident species had smaller overall body lengths when compared with the marine migrant species. In addition, the estuarine resident species had smaller modal size classes in the closed estuaries when compared with the open estuaries. These differences may be linked to the foraging strategies of the species, as well as food availability and different levels of predation in the different estuary types. The marine migrant species did not show any trends in this respect although the closed systems had the largest individuals for all four dominant marine species. This finding may be linked to the inability of these species to breed in closed estuaries, thus channelling reproductive energy resources into somatic growth. In addition, prolonged periods of mouth closure prevent the emigration of large individuals back to the sea. Otter trawling was conducted in fiye estuaries and captured mostly demersal species. The otter trawl data confirmed the seine net community analysis, with significantly different communities identified in the permanently open and intermittently open estuaries (p=0.02), as well as in the small and large intermittently open estuaries (p=0.03). The environmental variables responsible for these community differences were mouth status and variables associated with estuarine size. The identification of estuary mouth status by this study as the most influential environmental factor is compounded by this "ariable affecting or being indicative of numerous other physico-chemical features. The large differences in the fish communities in different estuary types indicate the importance of each estuary type to various species. This should be taken into account before allowing any form of commercial fishing in these important nursery areas.
- Full Text:
- Date Issued: 2001
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
Invasion status and impact potential of Florida bass Micropterus floridanus in South Africa
- Authors: Khosa, Dumisani
- Date: 2020
- Subjects: Micropterus floridanus , Florida largemouth bass -- South Africa , Black bass -- South Africa , Micropterus floridanus -- South Africa -- Habitat , Florida largemouth bass -- South Africa -- Habitat , Black bass -- South Africa -- Habitat , Introduced fishes -- Environmental aspects -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/165733 , vital:41276
- Description: In South Africa, the introduction of alien fishes was largely driven by the development of recreational fishing opportunities. Government-backed programmes resulted in the introduction of four Black Bass species: Micropterus salmoides, Micropterus dolomieu, Micropterus punctulatus and Micropterus floridanus. These species are regarded as the primary threat to native biota and there is an urgent need to assess their spread and impacts. This thesis focuses on: assessing the current distribution of all four Black Basses; using genetic techniques to establish the extent of hybridisation between M. salmoides and M. floridanus, and using functional responses to assess the impact potential of M. salmoides and M. floridanus under the context dependence of temperatures and habitat complexity. Maximum entropy modelling of habitat suitability for Black Bass highlighted that M. salmoides had broad climatic suitability across South Africa, while suitability for M. dolomieu and M. punctulatus was restricted to the Cape Fold Ecoregion. An extensive area-based invasion debt was observed for all Micropterus spp. To better understand the dynamics of hybridisation between M. salmoides and M. floridanus, 38 species-diagnostic single nucleotide polymorphism was used to screen Black Bass populations from the Breede River and Kowie River catchments. Micropterus salmoides alleles were more prevalent than M. floridanus in both the Breede River catchments (69.1% and 30.9%, respectively) and Kowie River catchments (63.3% and 36.7%, respectively). However, isolated populations found in dams (reservoirs) remained free from hybridisation. To compare resource utilisation (i.e. per capita effects) between M. salmoides and M. floridanus, two experimental chapters were designed. Chapter 4 focuses on how temperature mitigates per capita effects between the two Black Basses. There was a significant decrease in per capita effects for M. salmoides with increasing temperatures, while the converse was true for M. floridanus. Chapter 5 gives an account of the influence of habitat complexity on per capita effects. The results showed that habitat complexity did mitigate per capita effects, specifically on M. floridanus, which showed a significant drop in per capita effects; however, no significant difference was recorded for M. salmoides. In the two experimental chapters, M. floridanus exhibited a superior per capita effect compared to M. salmoides, implying higher predation impact on native biota.
- Full Text:
- Date Issued: 2020
- Authors: Khosa, Dumisani
- Date: 2020
- Subjects: Micropterus floridanus , Florida largemouth bass -- South Africa , Black bass -- South Africa , Micropterus floridanus -- South Africa -- Habitat , Florida largemouth bass -- South Africa -- Habitat , Black bass -- South Africa -- Habitat , Introduced fishes -- Environmental aspects -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/165733 , vital:41276
- Description: In South Africa, the introduction of alien fishes was largely driven by the development of recreational fishing opportunities. Government-backed programmes resulted in the introduction of four Black Bass species: Micropterus salmoides, Micropterus dolomieu, Micropterus punctulatus and Micropterus floridanus. These species are regarded as the primary threat to native biota and there is an urgent need to assess their spread and impacts. This thesis focuses on: assessing the current distribution of all four Black Basses; using genetic techniques to establish the extent of hybridisation between M. salmoides and M. floridanus, and using functional responses to assess the impact potential of M. salmoides and M. floridanus under the context dependence of temperatures and habitat complexity. Maximum entropy modelling of habitat suitability for Black Bass highlighted that M. salmoides had broad climatic suitability across South Africa, while suitability for M. dolomieu and M. punctulatus was restricted to the Cape Fold Ecoregion. An extensive area-based invasion debt was observed for all Micropterus spp. To better understand the dynamics of hybridisation between M. salmoides and M. floridanus, 38 species-diagnostic single nucleotide polymorphism was used to screen Black Bass populations from the Breede River and Kowie River catchments. Micropterus salmoides alleles were more prevalent than M. floridanus in both the Breede River catchments (69.1% and 30.9%, respectively) and Kowie River catchments (63.3% and 36.7%, respectively). However, isolated populations found in dams (reservoirs) remained free from hybridisation. To compare resource utilisation (i.e. per capita effects) between M. salmoides and M. floridanus, two experimental chapters were designed. Chapter 4 focuses on how temperature mitigates per capita effects between the two Black Basses. There was a significant decrease in per capita effects for M. salmoides with increasing temperatures, while the converse was true for M. floridanus. Chapter 5 gives an account of the influence of habitat complexity on per capita effects. The results showed that habitat complexity did mitigate per capita effects, specifically on M. floridanus, which showed a significant drop in per capita effects; however, no significant difference was recorded for M. salmoides. In the two experimental chapters, M. floridanus exhibited a superior per capita effect compared to M. salmoides, implying higher predation impact on native biota.
- Full Text:
- Date Issued: 2020
Invasion status and potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819 in the Kariega River, Eastern Cape, South Africa
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7586 , vital:21276
- Description: The impact of alien invasive species is one of the greatest threats to biodiversity globally. All of the major drainages of South Africa are invaded by non-native fishes, yet little information is available on their impact. This thesis focusses on providing a better understanding of the potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819, a species introduced into South Africa from the USA in 1938. The study assesses the distribution, establishment success and feeding ecology of L. macrochirus in an invaded South African River system in order to better understand and document its potential impacts. Specifically; this thesis (1) assesses the distribution and relative abundance of L. macrochirus in the Kariega System of the Eastern Cape, (2) determines the diet of the species in one of the major impoundments of the system, and (3) uses an experimental comparative functional response approach to assess whether this species has heightened predatory capabilities when compared with fishes with which it cooccurs. Ninety-six sites in the Kariega River system were sampled from the headwaters down to the estuary. Small native fish species (Enteromius anoplus and Enteromius pallidus) occurred mostly in the upper reaches, while in the middle and lower reaches, the centrarchid alien largemouth bass Micropterus salmoides and bluegill L. mocrochirus dominated. There was overlap between the centrarchids and introduced banded tilapia Tilapia sparrmanii and southern mouthbrooder Pseudocrenilabrus philander, but never with small-bodied native species. The stomach contents of L. macrochirus were examined during winter and summer and prey were identified to family level. Crustaceans and insects were an important component in their diet, but in summer fish eggs were common. Comparisons of bluegill diet with published literature indicated that there was potential for competition with largemouth bass, banded tilapia and southern mouthbrooder. Feeding experiments were conducted to compare the functional responses of these four species using a common prey item. Banded tilapia had significantly lower attack rates than the other species with no significant difference observed in other species. Bluegill has a similar impact to that of banded tilapia and southern mouthbrooder, but lower than that of largemouth bass. Results of the present study highlight that L. macrochirus introduced into dams will likely result in both upstream and downstream invasion of river systems. It is likely that this species does not, however, have as much of a predatory impact as M. salmoides in that its predatory capacity is relatively reduced and more comparable to South African native cichlids. These results are discussed within the context of invasion success/failure in other regions of southern Africa.
- Full Text:
- Date Issued: 2017
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7586 , vital:21276
- Description: The impact of alien invasive species is one of the greatest threats to biodiversity globally. All of the major drainages of South Africa are invaded by non-native fishes, yet little information is available on their impact. This thesis focusses on providing a better understanding of the potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819, a species introduced into South Africa from the USA in 1938. The study assesses the distribution, establishment success and feeding ecology of L. macrochirus in an invaded South African River system in order to better understand and document its potential impacts. Specifically; this thesis (1) assesses the distribution and relative abundance of L. macrochirus in the Kariega System of the Eastern Cape, (2) determines the diet of the species in one of the major impoundments of the system, and (3) uses an experimental comparative functional response approach to assess whether this species has heightened predatory capabilities when compared with fishes with which it cooccurs. Ninety-six sites in the Kariega River system were sampled from the headwaters down to the estuary. Small native fish species (Enteromius anoplus and Enteromius pallidus) occurred mostly in the upper reaches, while in the middle and lower reaches, the centrarchid alien largemouth bass Micropterus salmoides and bluegill L. mocrochirus dominated. There was overlap between the centrarchids and introduced banded tilapia Tilapia sparrmanii and southern mouthbrooder Pseudocrenilabrus philander, but never with small-bodied native species. The stomach contents of L. macrochirus were examined during winter and summer and prey were identified to family level. Crustaceans and insects were an important component in their diet, but in summer fish eggs were common. Comparisons of bluegill diet with published literature indicated that there was potential for competition with largemouth bass, banded tilapia and southern mouthbrooder. Feeding experiments were conducted to compare the functional responses of these four species using a common prey item. Banded tilapia had significantly lower attack rates than the other species with no significant difference observed in other species. Bluegill has a similar impact to that of banded tilapia and southern mouthbrooder, but lower than that of largemouth bass. Results of the present study highlight that L. macrochirus introduced into dams will likely result in both upstream and downstream invasion of river systems. It is likely that this species does not, however, have as much of a predatory impact as M. salmoides in that its predatory capacity is relatively reduced and more comparable to South African native cichlids. These results are discussed within the context of invasion success/failure in other regions of southern Africa.
- Full Text:
- Date Issued: 2017
Investigations into the dietary protein requirements of juvenile spotted grunter, Pomadasys commersonnii (Haemulidae : Pisces)
- Authors: Irish, Abigail
- Date: 1997
- Subjects: Fishes -- Nutrition , Pomadasys -- Nutrition , Grunts (Fishes) -- Nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5292 , http://hdl.handle.net/10962/d1005137 , Fishes -- Nutrition , Pomadasys -- Nutrition , Grunts (Fishes) -- Nutrition
- Description: The proximate composition of juvenile spotted grunter, Pomadasys commersonnii and their major prey items were analyzed to test the hypothesis that the dietary protein requirements would approximate the composition of the natural diet. The amino acid profile of juvenile P. commersonnii was analyzed to establish the pattern of limiting amino acids for this species. Juvenile P. commersonnii feed primarily on the mysid, Mesopodopsis slabberi, which has a protein content of 58.27±0.04% and a calorific value of 19.2kJ/g. The first-limiting essential amino acid for this fish was found to be lysine and it was predicted that the optimal dietary protein requirement would be between 50 and 60%. The optimal dietary protein inclusion level was investigated by feeding semi-purified diets containing graded levels of protein, ranging from 37-62%. Maximum growth was found to occur at dietary protein levels ranging from 40-51%. The best food conversion ratio was achieved at 56% dietary protein and the best protein efficiency ratio was obtained at a dietary protein inclusion level of 37-40%. The protein to energy ratio was defined by feeding 3 different protein levels at 3 different P:E levels. These semi-purified diets contained 35, 45 or 55% protein and 6, 8 or 12% dietary lipid, resulting in protein to energy ratios ranging from 21.1 to 42.3mg/kJ. The optimal P:E ratio for this species was found to be 26.7mg/kJ. This diet effected a low food conversion ratio (1.72±0.19), a low hepatosomatic index (4.01±0.23) and a high specific growth rate (5.96±0.36). The essential amino acid requirements of juvenile P. commersonnii were investigated. Semi-purified diets were formulated to contain graded levels of crystalline lysine based on the amino acid profile of the whole body and fed to the fish for a period of 60 days. Fish fed the "ideal protein" diet had significantly higher (p<0.05) specific growth rates (2.95±0.18), protein efficiency ratios (0.41±0.05) and significantly lower (p<0.05) food conversion ratios (3.02±0.29). Lysine levels in the whole body increased with increasing levels of supplemented lysine. The dietary requirement of lysine was found to be 4.30% of dietary protein. The crude protein digestibility of six protein sources was investigated. Diets were prepared with 1% chromic oxide as an internal marker. The tested protein sources included low temperature Danish fishmeal, steam dried Chilean fishmeal, blood meal, carcass meal, defatted soyabean meal and Spirulina meal. These potential fishmeal substitutes were selected due to their favourable amino acid profiles, and in particular their high levels of lysine, and their high protein content. Both the animal and the plant protein sources were highly digestible. Digestibility co-efficients ranged from 66.09% for Spirulina meal to 73.38% for low temperature Danish fishmeal. The results have shown that juvenile spotted grunter require a minimum of 40% crude protein in their diet, a P:E ratio of 26.7mg/kJ and a lysine concentration of 4.30% of the dietary protein. Long term growth trials are needed to confirm these results. The hypothesis that the proximate composition of the natural diet, and the proximate composition of the animal under investigation, provides a reliable indication of the animals' nutritional requirements was shown to be valid. Differences between the predicted, and the empirically determined optimal protein and protein:energy ratios were slight.
- Full Text:
- Date Issued: 1997
- Authors: Irish, Abigail
- Date: 1997
- Subjects: Fishes -- Nutrition , Pomadasys -- Nutrition , Grunts (Fishes) -- Nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5292 , http://hdl.handle.net/10962/d1005137 , Fishes -- Nutrition , Pomadasys -- Nutrition , Grunts (Fishes) -- Nutrition
- Description: The proximate composition of juvenile spotted grunter, Pomadasys commersonnii and their major prey items were analyzed to test the hypothesis that the dietary protein requirements would approximate the composition of the natural diet. The amino acid profile of juvenile P. commersonnii was analyzed to establish the pattern of limiting amino acids for this species. Juvenile P. commersonnii feed primarily on the mysid, Mesopodopsis slabberi, which has a protein content of 58.27±0.04% and a calorific value of 19.2kJ/g. The first-limiting essential amino acid for this fish was found to be lysine and it was predicted that the optimal dietary protein requirement would be between 50 and 60%. The optimal dietary protein inclusion level was investigated by feeding semi-purified diets containing graded levels of protein, ranging from 37-62%. Maximum growth was found to occur at dietary protein levels ranging from 40-51%. The best food conversion ratio was achieved at 56% dietary protein and the best protein efficiency ratio was obtained at a dietary protein inclusion level of 37-40%. The protein to energy ratio was defined by feeding 3 different protein levels at 3 different P:E levels. These semi-purified diets contained 35, 45 or 55% protein and 6, 8 or 12% dietary lipid, resulting in protein to energy ratios ranging from 21.1 to 42.3mg/kJ. The optimal P:E ratio for this species was found to be 26.7mg/kJ. This diet effected a low food conversion ratio (1.72±0.19), a low hepatosomatic index (4.01±0.23) and a high specific growth rate (5.96±0.36). The essential amino acid requirements of juvenile P. commersonnii were investigated. Semi-purified diets were formulated to contain graded levels of crystalline lysine based on the amino acid profile of the whole body and fed to the fish for a period of 60 days. Fish fed the "ideal protein" diet had significantly higher (p<0.05) specific growth rates (2.95±0.18), protein efficiency ratios (0.41±0.05) and significantly lower (p<0.05) food conversion ratios (3.02±0.29). Lysine levels in the whole body increased with increasing levels of supplemented lysine. The dietary requirement of lysine was found to be 4.30% of dietary protein. The crude protein digestibility of six protein sources was investigated. Diets were prepared with 1% chromic oxide as an internal marker. The tested protein sources included low temperature Danish fishmeal, steam dried Chilean fishmeal, blood meal, carcass meal, defatted soyabean meal and Spirulina meal. These potential fishmeal substitutes were selected due to their favourable amino acid profiles, and in particular their high levels of lysine, and their high protein content. Both the animal and the plant protein sources were highly digestible. Digestibility co-efficients ranged from 66.09% for Spirulina meal to 73.38% for low temperature Danish fishmeal. The results have shown that juvenile spotted grunter require a minimum of 40% crude protein in their diet, a P:E ratio of 26.7mg/kJ and a lysine concentration of 4.30% of the dietary protein. Long term growth trials are needed to confirm these results. The hypothesis that the proximate composition of the natural diet, and the proximate composition of the animal under investigation, provides a reliable indication of the animals' nutritional requirements was shown to be valid. Differences between the predicted, and the empirically determined optimal protein and protein:energy ratios were slight.
- Full Text:
- Date Issued: 1997
Investigations into the dietary requirements of Clarias gariepinus larvae (Pisces : Clariidae) and the formulation and manufacture of an artificial dry feed for use in intensive larval rearing
- Authors: Uys, Wynand
- Date: 1984
- Subjects: Clarias gariepinus Catfishes -- Africa Clariidae Catfishes -- Africa -- Nutrition -- Requirements Clarias
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5205 , http://hdl.handle.net/10962/d1004446
- Description: The need for developing an artificial dry feed for Clarias gariepinus larvae was identified. Dry larval fishfeed requires certain physical properties. Techniques for manufacturing feeds which comply with these requirements were evolved and are recomended for practical use. The techniques that were used for artificial reproduction of C. gariepinus larvae are briefly discussed. The larvae were fed on various dietary formulations and their growth responses were monitored in order to determine their nutritional requirements. A feed was developed which gave superior results to those obtained with natural food organisms. This feed consisted of Torula yeast(69,8%), fishmeal(23,3%), vitamin supplements(O,9%), methionine supplement (150mg/kg), bactericide and preservatives. The feed particles were coated with a lipid supplement which was added at a ratio of 6% to the weight of the feed. The optimum particle size (diameter) for C. gariepinus larvae is 2,2% of their mean total length. The larvae should be given a feed ration of 25% of body weight per day at a frequency of once every four hours. A favourable feed conversion ratio of 1.1g of feed consumed per gram of larval weight gain was experienced. The established dry feed is suitable for use in commercial hatcheries and can be used as a standard and proven food source for further research on the intensive rearing of C. gariepinus larvae.
- Full Text:
- Date Issued: 1984
- Authors: Uys, Wynand
- Date: 1984
- Subjects: Clarias gariepinus Catfishes -- Africa Clariidae Catfishes -- Africa -- Nutrition -- Requirements Clarias
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5205 , http://hdl.handle.net/10962/d1004446
- Description: The need for developing an artificial dry feed for Clarias gariepinus larvae was identified. Dry larval fishfeed requires certain physical properties. Techniques for manufacturing feeds which comply with these requirements were evolved and are recomended for practical use. The techniques that were used for artificial reproduction of C. gariepinus larvae are briefly discussed. The larvae were fed on various dietary formulations and their growth responses were monitored in order to determine their nutritional requirements. A feed was developed which gave superior results to those obtained with natural food organisms. This feed consisted of Torula yeast(69,8%), fishmeal(23,3%), vitamin supplements(O,9%), methionine supplement (150mg/kg), bactericide and preservatives. The feed particles were coated with a lipid supplement which was added at a ratio of 6% to the weight of the feed. The optimum particle size (diameter) for C. gariepinus larvae is 2,2% of their mean total length. The larvae should be given a feed ration of 25% of body weight per day at a frequency of once every four hours. A favourable feed conversion ratio of 1.1g of feed consumed per gram of larval weight gain was experienced. The established dry feed is suitable for use in commercial hatcheries and can be used as a standard and proven food source for further research on the intensive rearing of C. gariepinus larvae.
- Full Text:
- Date Issued: 1984
Investigations into the larval rearing of two South African sparid species
- Authors: Davis, Jerome Adam
- Date: 1997
- Subjects: Sparidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5293 , http://hdl.handle.net/10962/d1005138 , Sparidae
- Description: The most significant bottleneck to the development of marine finfish culture is a reliable production of juveniles for growout. This is due to the small size at hatch and delicate nature of the pelagic larvae produced by most commercially desirable species. However, over the last 30 years, improved larviculture techniques have been developed to the extent that many species are being successfully cultured worldwide. These techniques were applied to two endemic species as a preliminary step towards establishing marine finfish aquaculture in South Africa. Adult roman Chtysoblephus laticeps and carpenter Argyrozona argyrozona (Pisces: Sparidae) were caught in the Tsitsikamma National Park. Both species responded to injection with pituitary extract, HCG and LHRHa, and were succesfully stripped up to 48 hours after injection. Fish were stripped twice, the second stripping producing better quality eggs. Chyrysoblephus laticeps also spawned naturally after injection with LHRHa. The fertilised eggs were incubated and the larvae reared in a fully recirculating seawater system. One batch of A. argyrozona and three batches of C. laticeps were reared through metamorphosis on a diet of enriched rotifers and Anemia, and inert foods, following commonly used rearing procedures. Both species followed developmental patterns of other cultured larvae, displaying typical critical stages; high mortalities at first-feeding and cannibalism from 26-30 days after hatch resulted in survival rates ranging from 0.1-0.5%. Growth, survival, size of gape at first-feeding, and ease of weaning onto an inert diet of C. laticeps was comparable to other species being reared for the first time, indicating some potential as a candidate species. The numbers of A. argyrozona larvae reared were insufficient to make comparisons with other studies. The adults also proved to be susceptible to physical damage while in captivity and were, therefore, considered unsuitable for aquaculture. The thesis describes the spawning procedure, the systems developed and the larval rearing process. The critical stages of first-feeding, swim bladder inflation, settlement and cannibalism are discussed and the development of the larvae described. The ontogeny of both species is described in detail. Both species displayed typical sparid developmental patterns, but differed with respect to pigmentation, head spination and morphometrics.
- Full Text:
- Date Issued: 1997
- Authors: Davis, Jerome Adam
- Date: 1997
- Subjects: Sparidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5293 , http://hdl.handle.net/10962/d1005138 , Sparidae
- Description: The most significant bottleneck to the development of marine finfish culture is a reliable production of juveniles for growout. This is due to the small size at hatch and delicate nature of the pelagic larvae produced by most commercially desirable species. However, over the last 30 years, improved larviculture techniques have been developed to the extent that many species are being successfully cultured worldwide. These techniques were applied to two endemic species as a preliminary step towards establishing marine finfish aquaculture in South Africa. Adult roman Chtysoblephus laticeps and carpenter Argyrozona argyrozona (Pisces: Sparidae) were caught in the Tsitsikamma National Park. Both species responded to injection with pituitary extract, HCG and LHRHa, and were succesfully stripped up to 48 hours after injection. Fish were stripped twice, the second stripping producing better quality eggs. Chyrysoblephus laticeps also spawned naturally after injection with LHRHa. The fertilised eggs were incubated and the larvae reared in a fully recirculating seawater system. One batch of A. argyrozona and three batches of C. laticeps were reared through metamorphosis on a diet of enriched rotifers and Anemia, and inert foods, following commonly used rearing procedures. Both species followed developmental patterns of other cultured larvae, displaying typical critical stages; high mortalities at first-feeding and cannibalism from 26-30 days after hatch resulted in survival rates ranging from 0.1-0.5%. Growth, survival, size of gape at first-feeding, and ease of weaning onto an inert diet of C. laticeps was comparable to other species being reared for the first time, indicating some potential as a candidate species. The numbers of A. argyrozona larvae reared were insufficient to make comparisons with other studies. The adults also proved to be susceptible to physical damage while in captivity and were, therefore, considered unsuitable for aquaculture. The thesis describes the spawning procedure, the systems developed and the larval rearing process. The critical stages of first-feeding, swim bladder inflation, settlement and cannibalism are discussed and the development of the larvae described. The ontogeny of both species is described in detail. Both species displayed typical sparid developmental patterns, but differed with respect to pigmentation, head spination and morphometrics.
- Full Text:
- Date Issued: 1997