A holistic approach in understanding the effects of dietary protein sources on the growth and reproductive development of farmed abalone, Haliotis midae
- Wu, Yu
- Authors: Wu, Yu
- Date: 2020
- Subjects: Abalones -- Nutrition , Abalones -- Reproduction , Abalones -- Growth , Abalone culture , Haliotis midae -- Nutrition , Haliotis midae -- Reproduction , Haliotis midae -- Growth , Haliotis midae fisheries
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167719 , vital:41506
- Description: The combination of fishmeal and soya in the formulated feed of farmed South African abalone, Haliotis midae, not only improved abalone growth, but also the sustainability of the compound diets by reducing the reliance on fishmeal. However, the presence of soya produced larger gonads compared to those of abalone fed kelp or single-source protein diets. There is an increasing drive to control sexual maturation and reduce undesirable spawning events in farmed abalone. However, the reasons for the reported effects of soya inclusion on the reproductive development of farmed H. midae remain unresolved. The aim of this research was to use a combination of techniques to contribute to the understanding of the relationship between growth, reproductive and nutritional physiology of farmed H. midae fed diets of varying protein sources. These techniques included stable isotope analysis (SIA), fatty acid analysis, gonad histological assessments and haemolymph sexsteroid hormone analysis. The objectives were to examine the allocation of protein and nutritional components to somatic and reproductive tissues. This study also included the first attempt to investigate the role that sex steroid hormones play during gametogenesis. Abalone (40 – 50 g abalone-1) were fed one of four diets: either a single-source protein-based diet, i.e., (1) fishmeal-only (FM) or (2) soya-only (S), or a combination diet of (3) fishmeal-soya (FM S) or (4) fishmeal-sunflower meal (FM SM). Sampling occurred in 45-day intervals over one year. Dietary protein source had an effect on the growth of abalone, with enhancements in growth linked to the combination of fishmeal and a plant-protein source. The fishmeal ingredient was the most utilised protein source throughout the temporal changes in protein allocation into somatic and reproductive tissue, followed by soya and then sunflower meal. The mean whole- body mass of abalone was significantly influenced by an interaction between time and dietary treatment, with average whole-body mass changing differently over time between treatments (RM-ANOVA, F(24, 96) = 2.13, p = 0.005). Overall, abalone that were fed FM S had higher mean whole-body mass values than abalone that were fed the single-protein based diets, while abalone that were fed FM SM were similar to animals from all dietary treatments (RMANOVA, F(3, 12) = 5.75, p = 0.01). Male abalone had significantly higher gonad bulk index (GBI) values compared to females (RM-ANOVA, F(1, 24) = 49.03, p < 0.001) and this was independent of dietary treatment. Within each sex, female abalone fed the FM S diet (15.92 ± 1.88 mm3 g-1) had significantly higher GBI values than abalone fed S (9.76 ± 1.08 mm3 g-1), while abalone fed FM (11.96 ± 1.71 mm3 g-1) and FM SM (11.90 ± 0.80 mm3 g-1) were similar to abalone from all other dietary treatments (Tukey’s HSD, p < 0.05). Male abalone fed the FM S (21.59 ± 2.10 mm3 g-1) and FM SM diet (19.30 ± 2.63 mm3 g-1) had similar GBI values and they were significantly higher than in abalone fed the S diet (14.74 ± 1.27 mm3 g-1), while abalone fed FM S had significantly higher GBI values than abalone that consumed the FM diet (15.08 ±1.63mm3 g-1) ( Tukey’s HSD, p < 0.05). Although sunflower meal was poorly utilised, it produced similar overall growth to abalone that were fed the FM S diets. Yet, feed conversion ratio values were significantly lower for abalone fed FM S (1.30 ± 0.13) compared to those in the other three treatments, with ratios ranging from 1.65 – 1.72 over the one-year. The fatty acid compositions of the somatic and gonadal tissues were similar between treatments (PERMANOVA, p = 0.21), while fatty acid composition was influenced by sampling day, tissue type and abalone sex (PERMANOVA, p < 0.05). The essential fatty acids (EFAs) eicosadienoic acid and a-linolenic acid were present in abalone tissue, but they were not detected in the diets, suggesting the important role that an alternate food source (e.g. farmed abalone also had access to diatoms) may have played and the ability that H. midae may have in converting long-chain polyunsaturated fatty acids from C18 precursors. A change in the abundance of EFAs in the gonad tissue during highest and lowest GBI values suggested that arachidonic, eicosapentaenoic, g-linolenic and linoleic acid were important in females, while eicosapentaenoic, eicosadienoic and a-linolenic acid were important for male reproductive development. Dietary protein sources had an effect on the frequency distribution of maturity stages, where females that were fed FM S produced more ripe gonads and more males that were fed FM SM contained testes that showed signs of ripeness over the one-year study. Although dietary protein influenced the sex steroid concentrations in females and males, exhibiting fluctuations throughout the one-year period, no distinct pattern linked to gametogenesis were observed. The results from this study illustrate: (1) the importance of conducting laboratory studies when implementing SIA and mixing models in aquaculture nutrition; (2) conducting nutritional studies on mature, grow-out abalone; and (3) assessing the importance of naturally occurring diatoms in their diet and their contribution to growth and reproduction. The novel contribution of this research towards abalone nutritional physiology, the implications of these findings to industry as well as potential considerations for future studies were addressed.
- Full Text:
- Date Issued: 2020
- Authors: Wu, Yu
- Date: 2020
- Subjects: Abalones -- Nutrition , Abalones -- Reproduction , Abalones -- Growth , Abalone culture , Haliotis midae -- Nutrition , Haliotis midae -- Reproduction , Haliotis midae -- Growth , Haliotis midae fisheries
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167719 , vital:41506
- Description: The combination of fishmeal and soya in the formulated feed of farmed South African abalone, Haliotis midae, not only improved abalone growth, but also the sustainability of the compound diets by reducing the reliance on fishmeal. However, the presence of soya produced larger gonads compared to those of abalone fed kelp or single-source protein diets. There is an increasing drive to control sexual maturation and reduce undesirable spawning events in farmed abalone. However, the reasons for the reported effects of soya inclusion on the reproductive development of farmed H. midae remain unresolved. The aim of this research was to use a combination of techniques to contribute to the understanding of the relationship between growth, reproductive and nutritional physiology of farmed H. midae fed diets of varying protein sources. These techniques included stable isotope analysis (SIA), fatty acid analysis, gonad histological assessments and haemolymph sexsteroid hormone analysis. The objectives were to examine the allocation of protein and nutritional components to somatic and reproductive tissues. This study also included the first attempt to investigate the role that sex steroid hormones play during gametogenesis. Abalone (40 – 50 g abalone-1) were fed one of four diets: either a single-source protein-based diet, i.e., (1) fishmeal-only (FM) or (2) soya-only (S), or a combination diet of (3) fishmeal-soya (FM S) or (4) fishmeal-sunflower meal (FM SM). Sampling occurred in 45-day intervals over one year. Dietary protein source had an effect on the growth of abalone, with enhancements in growth linked to the combination of fishmeal and a plant-protein source. The fishmeal ingredient was the most utilised protein source throughout the temporal changes in protein allocation into somatic and reproductive tissue, followed by soya and then sunflower meal. The mean whole- body mass of abalone was significantly influenced by an interaction between time and dietary treatment, with average whole-body mass changing differently over time between treatments (RM-ANOVA, F(24, 96) = 2.13, p = 0.005). Overall, abalone that were fed FM S had higher mean whole-body mass values than abalone that were fed the single-protein based diets, while abalone that were fed FM SM were similar to animals from all dietary treatments (RMANOVA, F(3, 12) = 5.75, p = 0.01). Male abalone had significantly higher gonad bulk index (GBI) values compared to females (RM-ANOVA, F(1, 24) = 49.03, p < 0.001) and this was independent of dietary treatment. Within each sex, female abalone fed the FM S diet (15.92 ± 1.88 mm3 g-1) had significantly higher GBI values than abalone fed S (9.76 ± 1.08 mm3 g-1), while abalone fed FM (11.96 ± 1.71 mm3 g-1) and FM SM (11.90 ± 0.80 mm3 g-1) were similar to abalone from all other dietary treatments (Tukey’s HSD, p < 0.05). Male abalone fed the FM S (21.59 ± 2.10 mm3 g-1) and FM SM diet (19.30 ± 2.63 mm3 g-1) had similar GBI values and they were significantly higher than in abalone fed the S diet (14.74 ± 1.27 mm3 g-1), while abalone fed FM S had significantly higher GBI values than abalone that consumed the FM diet (15.08 ±1.63mm3 g-1) ( Tukey’s HSD, p < 0.05). Although sunflower meal was poorly utilised, it produced similar overall growth to abalone that were fed the FM S diets. Yet, feed conversion ratio values were significantly lower for abalone fed FM S (1.30 ± 0.13) compared to those in the other three treatments, with ratios ranging from 1.65 – 1.72 over the one-year. The fatty acid compositions of the somatic and gonadal tissues were similar between treatments (PERMANOVA, p = 0.21), while fatty acid composition was influenced by sampling day, tissue type and abalone sex (PERMANOVA, p < 0.05). The essential fatty acids (EFAs) eicosadienoic acid and a-linolenic acid were present in abalone tissue, but they were not detected in the diets, suggesting the important role that an alternate food source (e.g. farmed abalone also had access to diatoms) may have played and the ability that H. midae may have in converting long-chain polyunsaturated fatty acids from C18 precursors. A change in the abundance of EFAs in the gonad tissue during highest and lowest GBI values suggested that arachidonic, eicosapentaenoic, g-linolenic and linoleic acid were important in females, while eicosapentaenoic, eicosadienoic and a-linolenic acid were important for male reproductive development. Dietary protein sources had an effect on the frequency distribution of maturity stages, where females that were fed FM S produced more ripe gonads and more males that were fed FM SM contained testes that showed signs of ripeness over the one-year study. Although dietary protein influenced the sex steroid concentrations in females and males, exhibiting fluctuations throughout the one-year period, no distinct pattern linked to gametogenesis were observed. The results from this study illustrate: (1) the importance of conducting laboratory studies when implementing SIA and mixing models in aquaculture nutrition; (2) conducting nutritional studies on mature, grow-out abalone; and (3) assessing the importance of naturally occurring diatoms in their diet and their contribution to growth and reproduction. The novel contribution of this research towards abalone nutritional physiology, the implications of these findings to industry as well as potential considerations for future studies were addressed.
- Full Text:
- Date Issued: 2020
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
Use of bioindicators and biomarkers to assess aquatic environmental contamination in selected urban wetlands in Uganda
- Authors: Naigaga, Irene
- Date: 2013
- Subjects: Indicators (Biology) Biochemical markers Environmental monitoring -- Uganda Water quality biological assessment -- Uganda Water -- Pollution -- Uganda Wetlands -- Monitoring -- Uganda Wetland management -- Uganda Aquatic resources -- Uganda Aquatic resources conservation -- Uganda Aquatic resources -- Management -- Uganda Fishes -- Histopathaology -- Uganda Urban ecology (Biology) -- Uganda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5198 , http://hdl.handle.net/10962/d1002603
- Description: Pollution of aquatic resources in Uganda is on the increase and the trends are expected to increase with increase in population size and urbanisation. Assessment and mitigation of the environmental impacts on water quality and biodiversity have now become necessary. The aim of the study was to integrate invertebrate and fish as bioindicators and fish histopathology as a biomarker in the assessment of water quality deterioration in urban wetlands in Uganda. The integration harnesses the advantages and counteracts the shortcomings of each method and thus builds a more robust diagnostic tool that gives a better view of the impacts to the entire ecosystem. Four endpoints which included, physicochemical variables, benthic macroinvertebrate bioindicators, fish bioindicators and fish histopathology biomarkers were compared between varied effluent-impacted wetlands (Murchison Bay in Kampala, and Kirinya, Masese and Winday Bay in Jinja) and a non-impacted reference wetland (Lwanika in Mayuge). Results from the effluent-impacted sites differed from the less impacted reference site. The two sampling locations at Murchison Bay (inshore and offshore) and one sampling location at Kirinya (inshore), that were highly impacted with urban effluent, showed elevated nutrient levels, low pH, dissolved oxygen and secchi depth readings. This corresponded with low invertebrate taxa and fish species diversity and richness; and severe histopathological responses in liver, gonads and gills of O. niloticus. Sensitive taxa such as ephemeroptera and trichoptera were completely absent while pollution tolerant taxa Chironomus sp, Corbicula and Oligochaeta were present. Also notable was the absence of many native haplochromines and presence of mainly Brycinus sadleri, Oreochromis niloticus and leucostictus. The organs manifested high prevalence of severe inflammatory and regressive changes and higher organ indices that fell within the pathological category. These sites were consistently classified as highly polluted under the four endpoints. The reference site was classified as least polluted while Masese and Winday Bay were moderately polluted. Results suggested that the approach of using invertebrate and fish as bioindicators and the fish histopathology as a biomarker, in relation to water quality physicochemical variables was a useful tool in highlighting the spatial differences in environmental quality.
- Full Text:
- Date Issued: 2013
- Authors: Naigaga, Irene
- Date: 2013
- Subjects: Indicators (Biology) Biochemical markers Environmental monitoring -- Uganda Water quality biological assessment -- Uganda Water -- Pollution -- Uganda Wetlands -- Monitoring -- Uganda Wetland management -- Uganda Aquatic resources -- Uganda Aquatic resources conservation -- Uganda Aquatic resources -- Management -- Uganda Fishes -- Histopathaology -- Uganda Urban ecology (Biology) -- Uganda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5198 , http://hdl.handle.net/10962/d1002603
- Description: Pollution of aquatic resources in Uganda is on the increase and the trends are expected to increase with increase in population size and urbanisation. Assessment and mitigation of the environmental impacts on water quality and biodiversity have now become necessary. The aim of the study was to integrate invertebrate and fish as bioindicators and fish histopathology as a biomarker in the assessment of water quality deterioration in urban wetlands in Uganda. The integration harnesses the advantages and counteracts the shortcomings of each method and thus builds a more robust diagnostic tool that gives a better view of the impacts to the entire ecosystem. Four endpoints which included, physicochemical variables, benthic macroinvertebrate bioindicators, fish bioindicators and fish histopathology biomarkers were compared between varied effluent-impacted wetlands (Murchison Bay in Kampala, and Kirinya, Masese and Winday Bay in Jinja) and a non-impacted reference wetland (Lwanika in Mayuge). Results from the effluent-impacted sites differed from the less impacted reference site. The two sampling locations at Murchison Bay (inshore and offshore) and one sampling location at Kirinya (inshore), that were highly impacted with urban effluent, showed elevated nutrient levels, low pH, dissolved oxygen and secchi depth readings. This corresponded with low invertebrate taxa and fish species diversity and richness; and severe histopathological responses in liver, gonads and gills of O. niloticus. Sensitive taxa such as ephemeroptera and trichoptera were completely absent while pollution tolerant taxa Chironomus sp, Corbicula and Oligochaeta were present. Also notable was the absence of many native haplochromines and presence of mainly Brycinus sadleri, Oreochromis niloticus and leucostictus. The organs manifested high prevalence of severe inflammatory and regressive changes and higher organ indices that fell within the pathological category. These sites were consistently classified as highly polluted under the four endpoints. The reference site was classified as least polluted while Masese and Winday Bay were moderately polluted. Results suggested that the approach of using invertebrate and fish as bioindicators and the fish histopathology as a biomarker, in relation to water quality physicochemical variables was a useful tool in highlighting the spatial differences in environmental quality.
- Full Text:
- Date Issued: 2013
The biology and systematics of South African pipefishes of the genus Syngnathus
- Authors: Mwale, Monica
- Date: 2007
- Subjects: Pipefishes -- South Africa Syngnathus -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5237 , http://hdl.handle.net/10962/d1005080
- Description: Syngnathus the most speciose genus in the family Syngnathidae is widely in the Atlantic and Eastern Pacific oceans. However, it is poorly represented in the Indian Ocean with the only two species, Syngnathus temminckii and S. watermeyeri occurring in Southern African estuaries and coastal areas. Syngnathus temminckii the most common South African pipefish has been synonymised with S. acus, as the morphological and genetic divergence between these two populations has not been documented. There is also uncertainty in the taxonomic status of S. watermeyeri, an endemic estuarine pipefish that is restricted to two Eastern Cape estuaries. The purpose of this study was therefore to compare biological, morphological and genetic variation of South African Syngnathus species among different populations/locations, and with European populations of S. acus. Sixteen meristic and ten morphometric characteristics were quantified from specimens obtained from field as well as various international natural history museum collections. Univariate (ANOVA) and multivariate (principal component analysis and discriminant analyses) analyses were used to assess morphological differences among the species. Morphometric variables were adjusted as ratios of the standard length and using an allometric procedure. ANCOVA analysis indicated significant differences between S. acus and S. temminckii for the relationships of the standard length (SL) and all morphological characters. There was no significant correlation between SL and snout length, snout depth, inter-orbital width and trunk depth for S. watermeyeri. The analyses provided evidence for distinct populations of S. acus, S. temminckii and S. watermeyeri although morphological character differentiation was greater between S. watermeyeri and the other two larger species. Although, significant differences were observed for meristic characters, pairwise comparisons did not reflect a clear pattern of variability. Most of the measured morphological characters contributed more than 70% to the morphological variation between the populations. Plot of the canonical scores for the variables resulted in the specimens clustering according to species groups and locations of S. temminckii. Sequences of 750 base pairs of the mitochondrial cytochrome gene from 11 localities were compared with published sequences of other species of Syngnathus. Phylogenetic analysis was performed using parsimony, maximum likelihood (ML) and Bayesian inference (BI). The South African species were revealed to be sister-taxa with about 6 % divergence, while S. temminckii and S. acus had about 11% sequence divergence. 20 haplotypes among 46 total specimens from the three species. Gene flow was estimated at approximately 3 migrants per generation between the two South African populations and about 1 per generation between S. temminckii and S. acus. Such strong stock structuring among presumably recently established post-Pliocene (< 2 Million years ago) populations suggests that these species are reproductively isolated. Morphological and genetic variation observed in this study combined with current knowledge of life history attributes of the South African pipefishes indicate that conservative management decisions are necessary until the patterns and extent of differentiation among populations species-wide can be investigated further. It is thus being proposed that the name of the South African population of S. acus be changed to Syngnathus temminckii (Kaup, 1856).
- Full Text:
- Date Issued: 2007
- Authors: Mwale, Monica
- Date: 2007
- Subjects: Pipefishes -- South Africa Syngnathus -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5237 , http://hdl.handle.net/10962/d1005080
- Description: Syngnathus the most speciose genus in the family Syngnathidae is widely in the Atlantic and Eastern Pacific oceans. However, it is poorly represented in the Indian Ocean with the only two species, Syngnathus temminckii and S. watermeyeri occurring in Southern African estuaries and coastal areas. Syngnathus temminckii the most common South African pipefish has been synonymised with S. acus, as the morphological and genetic divergence between these two populations has not been documented. There is also uncertainty in the taxonomic status of S. watermeyeri, an endemic estuarine pipefish that is restricted to two Eastern Cape estuaries. The purpose of this study was therefore to compare biological, morphological and genetic variation of South African Syngnathus species among different populations/locations, and with European populations of S. acus. Sixteen meristic and ten morphometric characteristics were quantified from specimens obtained from field as well as various international natural history museum collections. Univariate (ANOVA) and multivariate (principal component analysis and discriminant analyses) analyses were used to assess morphological differences among the species. Morphometric variables were adjusted as ratios of the standard length and using an allometric procedure. ANCOVA analysis indicated significant differences between S. acus and S. temminckii for the relationships of the standard length (SL) and all morphological characters. There was no significant correlation between SL and snout length, snout depth, inter-orbital width and trunk depth for S. watermeyeri. The analyses provided evidence for distinct populations of S. acus, S. temminckii and S. watermeyeri although morphological character differentiation was greater between S. watermeyeri and the other two larger species. Although, significant differences were observed for meristic characters, pairwise comparisons did not reflect a clear pattern of variability. Most of the measured morphological characters contributed more than 70% to the morphological variation between the populations. Plot of the canonical scores for the variables resulted in the specimens clustering according to species groups and locations of S. temminckii. Sequences of 750 base pairs of the mitochondrial cytochrome gene from 11 localities were compared with published sequences of other species of Syngnathus. Phylogenetic analysis was performed using parsimony, maximum likelihood (ML) and Bayesian inference (BI). The South African species were revealed to be sister-taxa with about 6 % divergence, while S. temminckii and S. acus had about 11% sequence divergence. 20 haplotypes among 46 total specimens from the three species. Gene flow was estimated at approximately 3 migrants per generation between the two South African populations and about 1 per generation between S. temminckii and S. acus. Such strong stock structuring among presumably recently established post-Pliocene (< 2 Million years ago) populations suggests that these species are reproductively isolated. Morphological and genetic variation observed in this study combined with current knowledge of life history attributes of the South African pipefishes indicate that conservative management decisions are necessary until the patterns and extent of differentiation among populations species-wide can be investigated further. It is thus being proposed that the name of the South African population of S. acus be changed to Syngnathus temminckii (Kaup, 1856).
- Full Text:
- Date Issued: 2007
The life history patterns of the polychaete, Terebrasabella heterouncinata, a pest of cultured abalone
- Authors: Simon, Carol Anne
- Date: 2005
- Subjects: Polychaeta -- Physiology Sabellidae -- Physiology Abalones -- Diseases Polychaeta -- Reproduction Sabellidae -- Reproduction Abalone culture -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5336 , http://hdl.handle.net/10962/d1005632
- Description: Terebrasabella heterouncinata is a small K-selected sabellid polychaete. It is a simultaneous hermaphrodite with a semi-continuous mode of reproduction, producing relatively few large eggs that are brooded within the parental burrow until the larvae emerge, to settle on the growing edge of the abalone shell. Despite its low fecundity, this worm has become problematic on abalone farms in South Africa. The present study was conducted to gain an understanding of the life history patterns of T. helerouncinata to determine how they contributed to the success of these worms under altered conditions. This study demonstrated that conditions prevalent on abalone farms were conducive to enhancing the reproductive success of this worm, and suggests that larger, more fecund worms may have been selected for in the decade that these worms have been present on the farms. Increased nutrient availability, and possibly the increased stability of the farm environment relative to its natural environment, has led to a 1.5-fold increase in the average size of the worms. Body size was found to be positively correlated with brood size, and this resulted in worms on farms brooding 3 to 4.5 times more offspring at a time than worms from wild abalone. The ability to increase the number of eggs produced at a time may have been limited by the fact that these worms have only two ovaries. Thus, the increase in fecundity may have been related primarily to the increase in the rate at which the eggs were laid by the worms on the farms, and the increase in the coelomic space available for the storage of these rapidly developing eggs. The ability to increase the rate at which oocytes develop may be related to the vitellogenic mechanisms employed by these worms. Vitellogenic oocytes are able to incorporate high molecular weight yolk precursors from the surrounding coelomic fluid through endocytotic activity. This may allow the oocytes to increase the rate at which they incorporate yolk material under conditions of nutrient enrichment. The increase in fecundity did not occur at the expense of offspring size and, presumably, quality. The increased reproductive output on the farms was compounded by a proportionate increase in the number of reproducing worms within the population. In addition, these worms are long-lived (worms from farmed abalone reached a maximum age of approximately 40 months) and exhibit negligible senescence. Thus, their reproductive output did not change significantly with an increase in age. Furthermore, the proportion of the reproductive worms did not decrease with an increase in age. Thus, within the age range tested, worms of all ages have the potential to make equal contributions to population growth. While diet and abalone stocking density could not be identified as having a significant effect on reproductive output and infestation rate under intensive culture conditions, it was demonstrated that in a naïve abalone population, the total intensity of infestation increased exponentially with time. This increase may be a consequence of an increase in fertilisation success. These worms continuously produce entaquasperm that are released into the water column. The sperm are collected by other individuals that then store the sperm in a single spermatheca. The ability to store sperm relieves individuals of a dependence on the synchronisation of spawning of eggs and sperm. As the population size and density increases, there could be more individuals releasing sperm into the water column, resulting in a continuous supply of sperm. The increased production of eggs would therefore not be constrained by a lack of sperm. The stored sperm are released into the brood chamber to fertilise eggs as they are laid, and this would probably increase the fertilisation success in the species. This study also provides evidence to suggest that reproduction in this worm has a seasonal component. Future studies should concentrate on measuring fertilisation success in greater detail, measuring the effect of season on reproduction, determining whether there are genetic differences between worms on farmed and wild abalone and determining whether wild worms have similar life-spans and age-related fecundity as worms on farms.
- Full Text:
- Date Issued: 2005
- Authors: Simon, Carol Anne
- Date: 2005
- Subjects: Polychaeta -- Physiology Sabellidae -- Physiology Abalones -- Diseases Polychaeta -- Reproduction Sabellidae -- Reproduction Abalone culture -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5336 , http://hdl.handle.net/10962/d1005632
- Description: Terebrasabella heterouncinata is a small K-selected sabellid polychaete. It is a simultaneous hermaphrodite with a semi-continuous mode of reproduction, producing relatively few large eggs that are brooded within the parental burrow until the larvae emerge, to settle on the growing edge of the abalone shell. Despite its low fecundity, this worm has become problematic on abalone farms in South Africa. The present study was conducted to gain an understanding of the life history patterns of T. helerouncinata to determine how they contributed to the success of these worms under altered conditions. This study demonstrated that conditions prevalent on abalone farms were conducive to enhancing the reproductive success of this worm, and suggests that larger, more fecund worms may have been selected for in the decade that these worms have been present on the farms. Increased nutrient availability, and possibly the increased stability of the farm environment relative to its natural environment, has led to a 1.5-fold increase in the average size of the worms. Body size was found to be positively correlated with brood size, and this resulted in worms on farms brooding 3 to 4.5 times more offspring at a time than worms from wild abalone. The ability to increase the number of eggs produced at a time may have been limited by the fact that these worms have only two ovaries. Thus, the increase in fecundity may have been related primarily to the increase in the rate at which the eggs were laid by the worms on the farms, and the increase in the coelomic space available for the storage of these rapidly developing eggs. The ability to increase the rate at which oocytes develop may be related to the vitellogenic mechanisms employed by these worms. Vitellogenic oocytes are able to incorporate high molecular weight yolk precursors from the surrounding coelomic fluid through endocytotic activity. This may allow the oocytes to increase the rate at which they incorporate yolk material under conditions of nutrient enrichment. The increase in fecundity did not occur at the expense of offspring size and, presumably, quality. The increased reproductive output on the farms was compounded by a proportionate increase in the number of reproducing worms within the population. In addition, these worms are long-lived (worms from farmed abalone reached a maximum age of approximately 40 months) and exhibit negligible senescence. Thus, their reproductive output did not change significantly with an increase in age. Furthermore, the proportion of the reproductive worms did not decrease with an increase in age. Thus, within the age range tested, worms of all ages have the potential to make equal contributions to population growth. While diet and abalone stocking density could not be identified as having a significant effect on reproductive output and infestation rate under intensive culture conditions, it was demonstrated that in a naïve abalone population, the total intensity of infestation increased exponentially with time. This increase may be a consequence of an increase in fertilisation success. These worms continuously produce entaquasperm that are released into the water column. The sperm are collected by other individuals that then store the sperm in a single spermatheca. The ability to store sperm relieves individuals of a dependence on the synchronisation of spawning of eggs and sperm. As the population size and density increases, there could be more individuals releasing sperm into the water column, resulting in a continuous supply of sperm. The increased production of eggs would therefore not be constrained by a lack of sperm. The stored sperm are released into the brood chamber to fertilise eggs as they are laid, and this would probably increase the fertilisation success in the species. This study also provides evidence to suggest that reproduction in this worm has a seasonal component. Future studies should concentrate on measuring fertilisation success in greater detail, measuring the effect of season on reproduction, determining whether there are genetic differences between worms on farmed and wild abalone and determining whether wild worms have similar life-spans and age-related fecundity as worms on farms.
- Full Text:
- Date Issued: 2005
Towards the development of a protocol for the selection of probiotics in marine fish larviculture
- Authors: Vine, Niall Gordon
- Date: 2005
- Subjects: Marine fishes -- Larvae Bacteria Fishes -- Microbiology Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5329 , http://hdl.handle.net/10962/d1005175
- Description: Manipulation or control of the microbiological aquaculture environment has been identified as an important focus area for future hatchery development. Subsequently, alternatives to obtain control of the microbiological environment are being sought of which the field of probiotics appears highly promising. Probiotics are usually selected based on various in vitro characteristics, however, the methods used differ and are sometimes unsuccessful due to poor experimentation. The aim of this work is to contribute towards the development of a protocol for the in vitro screening of bacterial candidate probiotics for marine fish larviculture. To reduce the number of candidate probiotics to be tested in vivo, various in vitro experiments need to be conducted, each screening for a particular mode of action – antagonism towards pathogen through production of antimicrobial compounds, growth and attachment to fish intestinal mucus, and the production of other beneficial compounds such as vitamins, fatty-acids and digestive enzymes. A total of 108 bacteria species were isolated from the digestive tract of the adult common clownfish, Amphiprion percula to screen for potential probiotics to be used in clownfish larval rearing. The antagonistic compounds assay identified twelve isolates which showed antagonism towards two or more aquatic pathogens. This was followed by an in vitro test that involved growing the organisms in fish intestinal mucus and modeling their growth parameters. A ranking index (RI) was developed using the lag period (λ) and doubling time (td) of the organism, where (1over λ x td) x 100. Five candidate probionts (AP1-AP5) with varied growth parameters were used for further in vitro experiments. The attachment to mucus assay introduced a novel tool for quantifying competition for attachment sites between candidate probionts and pathogens on mucus. Candidate probiont Pseudoalteromonas AP5 reduced the attachment ability of Vibrio alginolyticus when added before the pathogen and partially out-competed the pathogen for attachment sites when added second. In vitro screening for the production of beneficial compounds tested the candidate probiotics’ ability to produce digestive enzymes - trypsin, lipase and alkaline phosphatase as well as carotenoids and vitamin C. Candidate probiont Pseudoalteromonas AP5 produced high levels of the enzymes (98.2, 34.1 and 91.3 mU product liberated.ml⁻¹, respectively) and contained carotenoids while Kocuria AP4 contained carotenoids but produced low quantities of enzymes (7.8, 0 and 59 mU product liberated.ml⁻¹, respectively). None of the candidate probiotics produced vitamin C. To eliminate potential pathogenic or toxic candidate probionts, Artemia nauplii were exposed to each candidate probiont and the percentage Artemia mortality after 24-hours was determined. Candidate probiont AP2 caused high mortality of Artemia nauplii (98.4%) and was excluded from further studies. Identification of candidate probionts AP3-AP5 was performed using 16S-rDNA molecular techniques and the bacteria were assigned the names Bacillus AP3, Kocuria AP4 and Pseudoalteromonas AP5, respectively. Two methods of larval probiont delivery were tested – attachment to Artemia, and in-water delivery. Attachment to Artemia was high for both Kocuria AP4 and Pseudoalteromonas AP5 (7.2 x10³ and 2.7x10⁴ bacteria.nauplius⁻¹, respectively) while the in-water viability experiment showed that Kocuria AP4 comprised 23.9% of the total culturable water microflora after 24 hours while Pseudoalteromonas AP5 contributed 100%. To validate the findings from the in vitro experiments, in vivo trials using clownfish larvae were performed. Of the four candidate probiotics tested, only Kocuria AP4 showed potential to increase larval survival. In vitro tests produced a better understanding of the possible mode of action and strategies of competition between bacteria, however, the number of criteria in which a candidate probiont is successful in vitro may not be the best predictor for its effectiveness in vivo. Commercial studies that reduce between-treatment variation are required to test predictions about the most suitable probiont or combinations thereof.
- Full Text:
- Date Issued: 2005
- Authors: Vine, Niall Gordon
- Date: 2005
- Subjects: Marine fishes -- Larvae Bacteria Fishes -- Microbiology Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5329 , http://hdl.handle.net/10962/d1005175
- Description: Manipulation or control of the microbiological aquaculture environment has been identified as an important focus area for future hatchery development. Subsequently, alternatives to obtain control of the microbiological environment are being sought of which the field of probiotics appears highly promising. Probiotics are usually selected based on various in vitro characteristics, however, the methods used differ and are sometimes unsuccessful due to poor experimentation. The aim of this work is to contribute towards the development of a protocol for the in vitro screening of bacterial candidate probiotics for marine fish larviculture. To reduce the number of candidate probiotics to be tested in vivo, various in vitro experiments need to be conducted, each screening for a particular mode of action – antagonism towards pathogen through production of antimicrobial compounds, growth and attachment to fish intestinal mucus, and the production of other beneficial compounds such as vitamins, fatty-acids and digestive enzymes. A total of 108 bacteria species were isolated from the digestive tract of the adult common clownfish, Amphiprion percula to screen for potential probiotics to be used in clownfish larval rearing. The antagonistic compounds assay identified twelve isolates which showed antagonism towards two or more aquatic pathogens. This was followed by an in vitro test that involved growing the organisms in fish intestinal mucus and modeling their growth parameters. A ranking index (RI) was developed using the lag period (λ) and doubling time (td) of the organism, where (1over λ x td) x 100. Five candidate probionts (AP1-AP5) with varied growth parameters were used for further in vitro experiments. The attachment to mucus assay introduced a novel tool for quantifying competition for attachment sites between candidate probionts and pathogens on mucus. Candidate probiont Pseudoalteromonas AP5 reduced the attachment ability of Vibrio alginolyticus when added before the pathogen and partially out-competed the pathogen for attachment sites when added second. In vitro screening for the production of beneficial compounds tested the candidate probiotics’ ability to produce digestive enzymes - trypsin, lipase and alkaline phosphatase as well as carotenoids and vitamin C. Candidate probiont Pseudoalteromonas AP5 produced high levels of the enzymes (98.2, 34.1 and 91.3 mU product liberated.ml⁻¹, respectively) and contained carotenoids while Kocuria AP4 contained carotenoids but produced low quantities of enzymes (7.8, 0 and 59 mU product liberated.ml⁻¹, respectively). None of the candidate probiotics produced vitamin C. To eliminate potential pathogenic or toxic candidate probionts, Artemia nauplii were exposed to each candidate probiont and the percentage Artemia mortality after 24-hours was determined. Candidate probiont AP2 caused high mortality of Artemia nauplii (98.4%) and was excluded from further studies. Identification of candidate probionts AP3-AP5 was performed using 16S-rDNA molecular techniques and the bacteria were assigned the names Bacillus AP3, Kocuria AP4 and Pseudoalteromonas AP5, respectively. Two methods of larval probiont delivery were tested – attachment to Artemia, and in-water delivery. Attachment to Artemia was high for both Kocuria AP4 and Pseudoalteromonas AP5 (7.2 x10³ and 2.7x10⁴ bacteria.nauplius⁻¹, respectively) while the in-water viability experiment showed that Kocuria AP4 comprised 23.9% of the total culturable water microflora after 24 hours while Pseudoalteromonas AP5 contributed 100%. To validate the findings from the in vitro experiments, in vivo trials using clownfish larvae were performed. Of the four candidate probiotics tested, only Kocuria AP4 showed potential to increase larval survival. In vitro tests produced a better understanding of the possible mode of action and strategies of competition between bacteria, however, the number of criteria in which a candidate probiont is successful in vitro may not be the best predictor for its effectiveness in vivo. Commercial studies that reduce between-treatment variation are required to test predictions about the most suitable probiont or combinations thereof.
- Full Text:
- Date Issued: 2005
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
On the use of metabolic rate measurements to assess the stress response in juvenile spotted grunter, Pomadasys commersonnii (Haemulidae, Pisces)
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
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