The effect of temperature and photoperiod on the digestive physiology of the South African abalone Haliotis midae
- Authors: Dixon, Mark Geoffrey
- Date: 1992
- Subjects: Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5276 , http://hdl.handle.net/10962/d1005120 , Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Description: Inadequate information of the nutritive physiology and the dietary requirements of abalone are the principle factors that currently limit the development of a formulated feed for the commercial culture of Haliotis midae. The need to develop a method to determine apparent digestibility co-efficient's for abalone in order to facilitate further applied nutritional research was identified. Animals between 50 and 80 mm were collected from natural stocks along the east Cape coast of South Africa at Port Alfred and Great Fish point, and acclimated to laboratory conditions. Initial trials demonstrated that H. midae accepted and preferred a semi-purified diet to the seaweed Plocamium corallorhiza, one of the main components of it's natural diet. A technique of determining apparent digestibility co-efficient's (ADC) using the indirect method with chromic oxide as an inert marker was developed. Digestibility trials yielded higher dry matter (DMADC) and crude protein apparent digestibility co-efficient's (CPADC) for the semi-purified diet than for two species of algae, Gelidium amanzii and P. corallorhiza (83.7% and 95.6%, 70.7% and 80.0%, and 29.9% and 57.3% respectively). The ability of the animals to utilize terrestrial animal and plant ingredients efficiently makes it feasible to use conventional feed ingredients in formulated feeds for H. midae. Trials to determine the effect of different temperatures (15°C, 18°C and 22°C) on DMADC and CPADC of the semipurified diet showed that peak digestibility occurred at 18°C. There was also a positive relationship between temperature and consumption rate. Although no enzyme studies with H. midae have been conducted, the peak ADC's at 18°C is attributed to an increase in enzyme activity at this temperature. Transit time, an inverse function of temperature and consumption, is considered to be responsible for the decrease in the ADC' s at 22°C in conjunction with a possible decrease in enzyme activity at this temperature. A photoperiod trial to investigate the effect of darkness on DMADC and CPADC of the semi-purified diet revealed that digestive efficiency decreased with increasing hours of darkness. There was also a positive relationship between duration of darkness and the rate of consumption. The decrease in ADC's is attributed to decreased transit times as the duration of darkness increased . The contribution of this project to the understanding of abalone nutrition, the development of a formulated abalone feed and systems design for abalone farms is discussed.
- Full Text:
- Authors: Dixon, Mark Geoffrey
- Date: 1992
- Subjects: Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5276 , http://hdl.handle.net/10962/d1005120 , Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Description: Inadequate information of the nutritive physiology and the dietary requirements of abalone are the principle factors that currently limit the development of a formulated feed for the commercial culture of Haliotis midae. The need to develop a method to determine apparent digestibility co-efficient's for abalone in order to facilitate further applied nutritional research was identified. Animals between 50 and 80 mm were collected from natural stocks along the east Cape coast of South Africa at Port Alfred and Great Fish point, and acclimated to laboratory conditions. Initial trials demonstrated that H. midae accepted and preferred a semi-purified diet to the seaweed Plocamium corallorhiza, one of the main components of it's natural diet. A technique of determining apparent digestibility co-efficient's (ADC) using the indirect method with chromic oxide as an inert marker was developed. Digestibility trials yielded higher dry matter (DMADC) and crude protein apparent digestibility co-efficient's (CPADC) for the semi-purified diet than for two species of algae, Gelidium amanzii and P. corallorhiza (83.7% and 95.6%, 70.7% and 80.0%, and 29.9% and 57.3% respectively). The ability of the animals to utilize terrestrial animal and plant ingredients efficiently makes it feasible to use conventional feed ingredients in formulated feeds for H. midae. Trials to determine the effect of different temperatures (15°C, 18°C and 22°C) on DMADC and CPADC of the semipurified diet showed that peak digestibility occurred at 18°C. There was also a positive relationship between temperature and consumption rate. Although no enzyme studies with H. midae have been conducted, the peak ADC's at 18°C is attributed to an increase in enzyme activity at this temperature. Transit time, an inverse function of temperature and consumption, is considered to be responsible for the decrease in the ADC' s at 22°C in conjunction with a possible decrease in enzyme activity at this temperature. A photoperiod trial to investigate the effect of darkness on DMADC and CPADC of the semi-purified diet revealed that digestive efficiency decreased with increasing hours of darkness. There was also a positive relationship between duration of darkness and the rate of consumption. The decrease in ADC's is attributed to decreased transit times as the duration of darkness increased . The contribution of this project to the understanding of abalone nutrition, the development of a formulated abalone feed and systems design for abalone farms is discussed.
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The ecology and culture of the rock catlet Chiloglanis pretoriae (Pisces : mochokidae)
- Authors: De Villiers, Pierre
- Date: 1991
- Subjects: Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5267 , http://hdl.handle.net/10962/d1005111 , Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Description: Chiloglanis pretoriae is a rock catlet, indigenous to southern Africa. The aim of the study was to develop a technique to culture C. pretoriae as an alternative to harvesting and selling wild caught fish on the international aquarium trade. As nothing was known about the culture of African rock catlets an investigation into the biology and ecology of the species was necessary to develop the culture protocol. Chiloglanis pretoriae inhabits fast flowing rapids (current speeds over 0.6 metres per second). It is a serial interstitial gravel spawner, that spawns during the summer months. Chiloglanis pretoriae is a carnivorous fish species, feeding on aquatic insects. The natural growth rate is relatively fast in the first two years where after it levels off. Sexual maturity (50%) is attained within the first year (44mm total length). From the four cell stage, embryos took seven days to hatch, 16 days to first feeding and 75 days to reach the juvenile phase. The free embryos were well developed and readily accepted artificial feed at first feeding. The fish spawned readily, without hormone induction, in a continuous raceway. Spawning in the 801 retangular glass aquaria was irregular. The substrate within the raceway consisted of gravel and large rocks. The current was maintained at 0.6m/sec, temperature at 26± 0.6⁰C, dissolved oxygen concentrations at 7.1± 0.3mg/l, pH at 6.9± 0.2 and photoperiod at 16L:8D. Conductivity was monitored and remained within the acceptable range of C. pretoriae (84± 10uS/m).
- Full Text:
- Authors: De Villiers, Pierre
- Date: 1991
- Subjects: Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5267 , http://hdl.handle.net/10962/d1005111 , Catfishes -- Africa , Catfishes -- Breeding -- Africa , Catfishes -- Ecology -- Africa , Fishes -- Cultural control -- Africa , Fishes -- Cultural control
- Description: Chiloglanis pretoriae is a rock catlet, indigenous to southern Africa. The aim of the study was to develop a technique to culture C. pretoriae as an alternative to harvesting and selling wild caught fish on the international aquarium trade. As nothing was known about the culture of African rock catlets an investigation into the biology and ecology of the species was necessary to develop the culture protocol. Chiloglanis pretoriae inhabits fast flowing rapids (current speeds over 0.6 metres per second). It is a serial interstitial gravel spawner, that spawns during the summer months. Chiloglanis pretoriae is a carnivorous fish species, feeding on aquatic insects. The natural growth rate is relatively fast in the first two years where after it levels off. Sexual maturity (50%) is attained within the first year (44mm total length). From the four cell stage, embryos took seven days to hatch, 16 days to first feeding and 75 days to reach the juvenile phase. The free embryos were well developed and readily accepted artificial feed at first feeding. The fish spawned readily, without hormone induction, in a continuous raceway. Spawning in the 801 retangular glass aquaria was irregular. The substrate within the raceway consisted of gravel and large rocks. The current was maintained at 0.6m/sec, temperature at 26± 0.6⁰C, dissolved oxygen concentrations at 7.1± 0.3mg/l, pH at 6.9± 0.2 and photoperiod at 16L:8D. Conductivity was monitored and remained within the acceptable range of C. pretoriae (84± 10uS/m).
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The stock identification of the Cape horse mackerel, Trachurus trachurus capensis (Pisces: Carangidae)
- Authors: Naish, Kerry-Ann
- Date: 1990
- Subjects: Carangidae -- Identification , Trachurus trachurus -- Identification , Carangidae -- South Africa , Trachurus trachurus -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5320 , http://hdl.handle.net/10962/d1005165 , Carangidae -- Identification , Trachurus trachurus -- Identification , Carangidae -- South Africa , Trachurus trachurus -- South Africa
- Description: Three stocks of the Cape horse mackerel, Trachurus trachurus capensis, have been recognised in the ICSEAF convention region off southern Africa (Figure 1) on the basis of catch distribution and biological analyses. They were identified as being off Namibia (ICSEAF Divisions 1 . 3 and 1.4), off the West Coast of South Africa (Div. 1.6) and off the South Coast (Div. 2.1 and 2.2). Recently, speculation as to the accuracy of the classification of the South African populations has arisen. The aim of this study was to determine the number of stocks In Divisions 1.6, 2.1 and 2.2, using methodology which assessed the spatial and temporal nature and the phenotypic and genotypic characteristics of the species. The distribution of horse mackerel was evaluated by studying the trends in catch data and length frequency distributions obtained from the demersal industry during 1986 to 1988 and from the demersal biomass cruises in 1987 and 1988. Adult fish, found in Div. 2.1 and 2.2, probably migrated; during the months in which horse mackerel were expected to spawn, CPUE values were higher over the central Agulhas Bank than in the east of the study region. During the quiescent period, catches and numbers were higher in the latter region. Juvenile horse mackerel were found in the nursery areas utilised by pelagic fish and it is likely that they were transported northward from the Agulhas Bank. A decrease in biomass of individuals in Div. 1.5 indicated a separation between a northern and a southern population. Analyses of the phenotype, or epigenetic characters, of horse mackerel were used as a further test of stock integrity. Monthly samples were drawn from Div. 1.6, 2.1 and 2.2 during May 1988 to June, 1989. Comparisons for the values obtained from growth, length-at-50%-maturity and the season of otolith ring formation from each region showed no significant variation in the phenotype. Morphometric analysis proved inconclusive. Monthly gonadosomatic indices show that fish south of the Orange River share the same spawning season. Reports from the literature show that horse mackerel in the latter region differ from those of northern Namibia in spawning season, age-at-50%-maturity and season of otolith ring formation. The genetic structure of the populations of horse mackerel was evaluated by means of a restriction enzyme analysis of the Mitochondrial DNA of 37 fish collected from Divisions 1.4, 1.5, 1.6, 2.1 and 2.2. Two composite genotypes of horse mackerel were found; one belonging to fish in Div. 1.4 and one to fish in Div. 1.6, 2.1 and 2.2. The genetic distance between the two genotypes, 0.07, was the expected distance between two populations at a subspecies level. Fish in Div. 1.5 consisted of both genotypes and may be a region of mixing between the two populations. The interpretation of results was cautioned; prevlous work has shown that the migration of a small number of individuals between two stocks can be expected to maintain a low variation between the populations. In concluding, it was recommended that the horse mackerel be managed as two stocks, one in Div. 1.3 and 1.4 and one in Div. 1.6, 2.1 and 2.2
- Full Text:
- Authors: Naish, Kerry-Ann
- Date: 1990
- Subjects: Carangidae -- Identification , Trachurus trachurus -- Identification , Carangidae -- South Africa , Trachurus trachurus -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5320 , http://hdl.handle.net/10962/d1005165 , Carangidae -- Identification , Trachurus trachurus -- Identification , Carangidae -- South Africa , Trachurus trachurus -- South Africa
- Description: Three stocks of the Cape horse mackerel, Trachurus trachurus capensis, have been recognised in the ICSEAF convention region off southern Africa (Figure 1) on the basis of catch distribution and biological analyses. They were identified as being off Namibia (ICSEAF Divisions 1 . 3 and 1.4), off the West Coast of South Africa (Div. 1.6) and off the South Coast (Div. 2.1 and 2.2). Recently, speculation as to the accuracy of the classification of the South African populations has arisen. The aim of this study was to determine the number of stocks In Divisions 1.6, 2.1 and 2.2, using methodology which assessed the spatial and temporal nature and the phenotypic and genotypic characteristics of the species. The distribution of horse mackerel was evaluated by studying the trends in catch data and length frequency distributions obtained from the demersal industry during 1986 to 1988 and from the demersal biomass cruises in 1987 and 1988. Adult fish, found in Div. 2.1 and 2.2, probably migrated; during the months in which horse mackerel were expected to spawn, CPUE values were higher over the central Agulhas Bank than in the east of the study region. During the quiescent period, catches and numbers were higher in the latter region. Juvenile horse mackerel were found in the nursery areas utilised by pelagic fish and it is likely that they were transported northward from the Agulhas Bank. A decrease in biomass of individuals in Div. 1.5 indicated a separation between a northern and a southern population. Analyses of the phenotype, or epigenetic characters, of horse mackerel were used as a further test of stock integrity. Monthly samples were drawn from Div. 1.6, 2.1 and 2.2 during May 1988 to June, 1989. Comparisons for the values obtained from growth, length-at-50%-maturity and the season of otolith ring formation from each region showed no significant variation in the phenotype. Morphometric analysis proved inconclusive. Monthly gonadosomatic indices show that fish south of the Orange River share the same spawning season. Reports from the literature show that horse mackerel in the latter region differ from those of northern Namibia in spawning season, age-at-50%-maturity and season of otolith ring formation. The genetic structure of the populations of horse mackerel was evaluated by means of a restriction enzyme analysis of the Mitochondrial DNA of 37 fish collected from Divisions 1.4, 1.5, 1.6, 2.1 and 2.2. Two composite genotypes of horse mackerel were found; one belonging to fish in Div. 1.4 and one to fish in Div. 1.6, 2.1 and 2.2. The genetic distance between the two genotypes, 0.07, was the expected distance between two populations at a subspecies level. Fish in Div. 1.5 consisted of both genotypes and may be a region of mixing between the two populations. The interpretation of results was cautioned; prevlous work has shown that the migration of a small number of individuals between two stocks can be expected to maintain a low variation between the populations. In concluding, it was recommended that the horse mackerel be managed as two stocks, one in Div. 1.3 and 1.4 and one in Div. 1.6, 2.1 and 2.2
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An assessment of the South African longline fishery with emphasis on stock integrity of kingklip, Genypterus capensis (Pisces : ophidiidae)
- Authors: Japp, David William
- Date: 1989
- Subjects: Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5209 , http://hdl.handle.net/10962/d1004660 , Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Description: The South African demersal longline experiment is assessed with emphasis on the target species, kingklip Genypterus capensis. The hypothesis that kingklip on the South African coast comprise a unit stock is tested. Recommendations for the management of the fishery are made. Longlining was found to be commercially viable. Techniques have been developed to target on either kingklip or the Cape hakes, Herluccius capensis and H. paradoxus. Longline fishermen exploit the kingklip spawner stock from August to No v ember by taking advantage of prespawning aggregations on the South-East Coast . Effort switches to the West Coast in late summer and early winter where kingklip are less abundant and a larger proportion of hake is caught. Catch rates of kingklip on the South Coast have declined sharply and the resource there has been exploited at a rate greater than that required to retain 50% of the unexploited biomass . There is a 17,6% probability that the spawner biomass on the South Coast has already been depleted below its pristine level. On the West Coast the catch rates of kingklip are lower than on the South Coast and have not changed significantly, although within the 95% confidence limits there is a possibility that the resource there has also been depleted below 50% of its pristine level. Genypterus capensis on the South African coast comprise a unit stock. Comparison of kingklip morphology using multivariate and discriminant function analysis and of otolith morphology using univariate statistics shows that there are no significant differences between the fish on the West and South Coasts. They are a slow growing species and were aged up to 25 years. Kingklip on the West Coast are smaller and have a lower L~ than those on the South Coast, but this is not a characteristic of discrete stocks. Kingklip on the South Coast mature earlier than those on the West Coast and aggregate to spawn on the South - East Coast in spring. There is no obvious spawning period on the West Coast. It is hypothesized that kingklip spawning on the South-East Coast is in response to favourable environmental conditions that enhances the survival of their eggs and larvae. It is recommended that demersal longlining be established as a permanent kingklip-directed fishery but that effort should not be allowed to increase. The West and South Coasts should be managed .separately. A TAC of 5 OOOt for kingklip should be introduced for 1989 of which 2 OOOt should be allocated to the West Coast and 3 OOOt to the South Coast . A closed season for kingklip from 1 August to 30 September on the South-East Coast is recommended. Hake-directed longlining should not be allowed as its effect on the hake spawner stocks are unknown and could be a potential threat to the stability of the demersal trawl fishery.
- Full Text:
- Authors: Japp, David William
- Date: 1989
- Subjects: Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5209 , http://hdl.handle.net/10962/d1004660 , Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Description: The South African demersal longline experiment is assessed with emphasis on the target species, kingklip Genypterus capensis. The hypothesis that kingklip on the South African coast comprise a unit stock is tested. Recommendations for the management of the fishery are made. Longlining was found to be commercially viable. Techniques have been developed to target on either kingklip or the Cape hakes, Herluccius capensis and H. paradoxus. Longline fishermen exploit the kingklip spawner stock from August to No v ember by taking advantage of prespawning aggregations on the South-East Coast . Effort switches to the West Coast in late summer and early winter where kingklip are less abundant and a larger proportion of hake is caught. Catch rates of kingklip on the South Coast have declined sharply and the resource there has been exploited at a rate greater than that required to retain 50% of the unexploited biomass . There is a 17,6% probability that the spawner biomass on the South Coast has already been depleted below its pristine level. On the West Coast the catch rates of kingklip are lower than on the South Coast and have not changed significantly, although within the 95% confidence limits there is a possibility that the resource there has also been depleted below 50% of its pristine level. Genypterus capensis on the South African coast comprise a unit stock. Comparison of kingklip morphology using multivariate and discriminant function analysis and of otolith morphology using univariate statistics shows that there are no significant differences between the fish on the West and South Coasts. They are a slow growing species and were aged up to 25 years. Kingklip on the West Coast are smaller and have a lower L~ than those on the South Coast, but this is not a characteristic of discrete stocks. Kingklip on the South Coast mature earlier than those on the West Coast and aggregate to spawn on the South - East Coast in spring. There is no obvious spawning period on the West Coast. It is hypothesized that kingklip spawning on the South-East Coast is in response to favourable environmental conditions that enhances the survival of their eggs and larvae. It is recommended that demersal longlining be established as a permanent kingklip-directed fishery but that effort should not be allowed to increase. The West and South Coasts should be managed .separately. A TAC of 5 OOOt for kingklip should be introduced for 1989 of which 2 OOOt should be allocated to the West Coast and 3 OOOt to the South Coast . A closed season for kingklip from 1 August to 30 September on the South-East Coast is recommended. Hake-directed longlining should not be allowed as its effect on the hake spawner stocks are unknown and could be a potential threat to the stability of the demersal trawl fishery.
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Some aspects of the ecology of the Eastern Cape rocky Sandelia Bainsii (Pisces : Anabantidae) in the Tyume River, Eastern Cape, South Africa
- Authors: Mayekiso, Monde
- Date: 1986
- Subjects: Anabantidae , Perciformes , Labyrinth fishes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5196 , http://hdl.handle.net/10962/d1001972 , Anabantidae , Perciformes , Labyrinth fishes
- Description: This is an account of some aspects of the ecology of the eastern Cape rocky, Sandelia bainsii Castelnau in the Tyume river in the eastern Cape. Previous unpublished work carried out by the Zoology Department of the University of Fort Hare in the mid-seventies indicated that the species was rare in the Tyume river. Because of its uncertain conservation status, its restricted geographic distribution and the lack of information on its biology, demography, feeding and reproductive biology were studied. The species occurs in the upper, middle and lower reaches of the Tyume river and is common in rocky , shallow habitats in the middle reaches of the system. The most important threats to the survival of S. bainsii appear to be habitat alteration and alien species. The presence of these threats and the small size of the population suggest that the species may be vulnerable to local extinction. As the total range of the species extends to only a few rivers in the eastern Cape, the species might face extinction if these threats are faced throughout its range. A detailed study on the autecology of S. bainsii was therefore carried out in order to provide a basis for rational conservation and management of the remaining populations of the species.The age structure and the growth rate of S. bainsii was determined using checks on scales and otoliths. Males grow faster and reach a larger size than females. The maximum length of S. bainsii is compared to that of other anabantids. The longevity of males is 5 years and that of females 3 years. Food preferences were determined by three different methods and the indices of relative importance of food items calculated for different length groups and seasons. S. bainsii was found to be an euryphagous and opportunistic predator whose diet consists largely of insects. A considerable overlap was found between the diet of S. bainsii and that of the two alien species, Salmo gairdneri and Micropterus salmoides which indicates a possibility of competition for food. Mark and recapture experiments showed that S. bainsii is a "sedentary " species which is unlikely to be seriously affected by man-made barriers to fish migration, such as weirs. The species reaches maturity during its second growing season (males 80 - 89mm and females 60 - 69mm) and the length at maturity is related to the modal length of males and females. A large proportion of the fish are thus mature at any given time. The fish spawn repeatedly during the summer breeding season, October to February resulting in near continuous recruitment. The possible adaptive value of this habit is discussed. An attempt is made to evaluate the life history style of S. bainsii in terms of the theory of r - and K- selection and altricial and precocial life history styles
- Full Text:
- Authors: Mayekiso, Monde
- Date: 1986
- Subjects: Anabantidae , Perciformes , Labyrinth fishes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5196 , http://hdl.handle.net/10962/d1001972 , Anabantidae , Perciformes , Labyrinth fishes
- Description: This is an account of some aspects of the ecology of the eastern Cape rocky, Sandelia bainsii Castelnau in the Tyume river in the eastern Cape. Previous unpublished work carried out by the Zoology Department of the University of Fort Hare in the mid-seventies indicated that the species was rare in the Tyume river. Because of its uncertain conservation status, its restricted geographic distribution and the lack of information on its biology, demography, feeding and reproductive biology were studied. The species occurs in the upper, middle and lower reaches of the Tyume river and is common in rocky , shallow habitats in the middle reaches of the system. The most important threats to the survival of S. bainsii appear to be habitat alteration and alien species. The presence of these threats and the small size of the population suggest that the species may be vulnerable to local extinction. As the total range of the species extends to only a few rivers in the eastern Cape, the species might face extinction if these threats are faced throughout its range. A detailed study on the autecology of S. bainsii was therefore carried out in order to provide a basis for rational conservation and management of the remaining populations of the species.The age structure and the growth rate of S. bainsii was determined using checks on scales and otoliths. Males grow faster and reach a larger size than females. The maximum length of S. bainsii is compared to that of other anabantids. The longevity of males is 5 years and that of females 3 years. Food preferences were determined by three different methods and the indices of relative importance of food items calculated for different length groups and seasons. S. bainsii was found to be an euryphagous and opportunistic predator whose diet consists largely of insects. A considerable overlap was found between the diet of S. bainsii and that of the two alien species, Salmo gairdneri and Micropterus salmoides which indicates a possibility of competition for food. Mark and recapture experiments showed that S. bainsii is a "sedentary " species which is unlikely to be seriously affected by man-made barriers to fish migration, such as weirs. The species reaches maturity during its second growing season (males 80 - 89mm and females 60 - 69mm) and the length at maturity is related to the modal length of males and females. A large proportion of the fish are thus mature at any given time. The fish spawn repeatedly during the summer breeding season, October to February resulting in near continuous recruitment. The possible adaptive value of this habit is discussed. An attempt is made to evaluate the life history style of S. bainsii in terms of the theory of r - and K- selection and altricial and precocial life history styles
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The effect of the pesticide, endosulfan, on hepatic cytochrome P-450, liver and gill ultrastructure, and selected haematological parameters of Oreochromis Mossambicus (Peters, 1852) (Pisces : Cichlidae)
- Authors: Quick, Arthur Joseph Rex
- Date: 1986
- Subjects: Pesticides , Mozambique tilapia , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5195 , http://hdl.handle.net/10962/d1001971 , Pesticides , Mozambique tilapia , Cichlids
- Description: Two possible ways in which fish may acclimate to prolonged exposure· to sublethal levels of endosulfan were investigated: induction of the hepatic monooxygenase system and changes in haematology. These studies also involved an examination of the ultrastructure of liver and gill tissue. Endosulfan caused none of the characteristic phenobarbital-type inductive effects on the liver of Oreochromis mossambicus. There was no increase in cytochrome P-450 levels, microsomal protein or hepatosomatic index. The reasons for the lack of induction are discussed. The effect of endosulfan on the following haematological parameters was determined: haemoglobin, erythrocyte count, microhaematocrit, mean erythrocyte volume and mean erythrocyte haemoglobin concentration. The only effect was an increase in erythrocyte count. The value of changes in haematological parameters as indicators of pollutioninduced anemia in the field is discussed. No changes in gill ultrastructure were noted although electron micrographs of liver tissue showed lesions in hepatocytes. The diagnostic value of pollution-induced pathological changes on cell ultrastructure are discussed. Recommendations are made with regard to future large scale application of pesticides on or near large water bodies
- Full Text:
- Authors: Quick, Arthur Joseph Rex
- Date: 1986
- Subjects: Pesticides , Mozambique tilapia , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5195 , http://hdl.handle.net/10962/d1001971 , Pesticides , Mozambique tilapia , Cichlids
- Description: Two possible ways in which fish may acclimate to prolonged exposure· to sublethal levels of endosulfan were investigated: induction of the hepatic monooxygenase system and changes in haematology. These studies also involved an examination of the ultrastructure of liver and gill tissue. Endosulfan caused none of the characteristic phenobarbital-type inductive effects on the liver of Oreochromis mossambicus. There was no increase in cytochrome P-450 levels, microsomal protein or hepatosomatic index. The reasons for the lack of induction are discussed. The effect of endosulfan on the following haematological parameters was determined: haemoglobin, erythrocyte count, microhaematocrit, mean erythrocyte volume and mean erythrocyte haemoglobin concentration. The only effect was an increase in erythrocyte count. The value of changes in haematological parameters as indicators of pollutioninduced anemia in the field is discussed. No changes in gill ultrastructure were noted although electron micrographs of liver tissue showed lesions in hepatocytes. The diagnostic value of pollution-induced pathological changes on cell ultrastructure are discussed. Recommendations are made with regard to future large scale application of pesticides on or near large water bodies
- Full Text: