The primary objective of this study was to examine environmental parameters thought to affect cannibalism in certain fish species. It was found that environmental, behavioural, genetic and physiological factors all affect cannibalism in the species exhibiting the phenomenon. The diversity of factors nfluencing cannibalism served to illustrate the complexity of this behaviour pattern. Feeding to satiation was found to suppress cannibalism in catfish, trout and koi carp. High population densities were found to increase the rate of cannibalism, thereby acting as a population regulation mechanism for catfish, trout and the common and koi carps. Live food, as compared with dry pelletized feed was found to significantly suppress cannibalistic aggression. Catfish grown in total darkness, provided with refuges and living in turbid conditions were found to exhibit lowered cannibalistic and territorial aggression. Various lines of evidence suggested that cannibalism has a genetic basis, as was shown by the differences in cannibalistic behaviour of the two strains of Cyprinus carpio, viz. common and koi carp, with cannibalism being higher in the latter. This finding substantiates the hypothesis that cannibalism is genetically controlled and therefore open to evolutionary change. It is concluded that cannibalism is adaptive in times of food limitation, but that it is merely a by-product of normal feeding behaviour when food is abundant. Since cannibalism is advantageous and thus adaptive, the question arises ai to whether selection is occurring at the individual or the population level (or both). It was concluded that it is acting at the individual level, and that any benefits accruing at the population level iv were simply the effect of the initial cause, viz. individual selection. One of the aims of this study was to determine whether cannibalistic tendencies in fish are influenced by differing life history style trajectories. Based on the results of this study it is hypothesized that cannibalism is an r-selected trait. wi th the understanding gained from the knowl edge of the fundamental principles governing cannibalism, certain recommendations for its control in fish culture could be made. It is, however, imperative that further intensive studies be carried out to understand more fully this complex subject. General "rules" for regulating cannibalism could be helpful for any given cannibalistic species. However, in considering the differing life-history styles of each species, it becomes evident that species-specific guidelines need to be worked out. Until then, any suggestions for cannibalistic control offered to the aquaculturist can only serve as unrefined tools.

In aquaculture, a thorough knowledge of the specific environmental requirements of a species is needed in order to maximize growth rate and survival. There is a paucity of data regarding the fundamental environmental requirements for the ongrowing phase of clownfish juveniles. This prompted the design of three experiments to determine the best feeding regimen, temperature and stocking density that maximize growth and survival of Amphiprion percula. Ration size and feeding frequency are important factors for optimizing fish growth during the juvenile grow-out phase. A factorial growth trial was conducted to determine the effect of feeding frequency and ration size on the growth of juvenile clownfish (Amphiprion percula).Three feeding frequencies (1, 2 and 3 times daily) and six rations (2,4,6,8, 10 and 12 % body weight per day (BW.day⁻¹)) were used to test the growth response over a twelve week period. Non-linear regression analysis on the effect of ration, independent of feeding frequency, on growth resulted in a significant (n = 36; r² = 68.7) parabolic model: In y = -0.0302x² + 0.5159x + -4.4377. Maximum growth corresponded to a ration of 8.5% BW.day⁻¹. Survival as a function of ration was significantly lower at 2% BW.day⁻¹. Data were further examined with Analysis of CoVariance (ANCOVA) to determine the effect of ration on growth at each feeding frequency. The combination revealed a maximum growth rate when the fish were fed a ration of 10% BW.day⁻¹ divided into two equal meals. The required ration per meal to maintain maximum growth was also found to decrease as feeding frequency increased. The determination of the best temperature for growth is of great importance due to the direct relationship between fish metabolism and temperature. The thermal preferendum of A. percula has already been estimated at 26 ± 0.7°C but it is not known whether this closely approximates the temperature for maximum growth. Sixteen tanks were set to different temperatures ranging between 21.5 and 30.2 °C. Ten juvenile A. percula were placed in each tank and growth was measured fortnightly over the course of the 10 week experiment. Non-linear regression analysis resulted in significant models for fish length (y = -0.0005x² + 0.00267x - 0.0338; r² = 56.7, n = 11) and weight (y= -0.00016x² + 0.0084x - 0.1073; r² = 61.6, n = 11). These models predict that maximum growth would be at 27.7 and 27.1 °C for length and weight, respectively. Temperature, over the range tested, had no apparent effect on survival. There was no significant difference between the temperatures for maximum growth and the preferred temperature. The effect of stocking densities ranging from 0.2 fish.L¹ to 4.0 fish.L⁻¹ on growth were used in the third experiment. The fish were fed to satiation twice daily and growth was measured fortnightly throughout the 8 week experiment. No effects on growth, survival or coefficient of variation were found within the range of stocking densities tested.

The proximate composition of juvenile spotted grunter, Pomadasys commersonnii and their major prey items were analyzed to test the hypothesis that the dietary protein requirements would approximate the composition of the natural diet. The amino acid profile of juvenile P. commersonnii was analyzed to establish the pattern of limiting amino acids for this species. Juvenile P. commersonnii feed primarily on the mysid, Mesopodopsis slabberi, which has a protein content of 58.27±0.04% and a calorific value of 19.2kJ/g. The first-limiting essential amino acid for this fish was found to be lysine and it was predicted that the optimal dietary protein requirement would be between 50 and 60%. The optimal dietary protein inclusion level was investigated by feeding semi-purified diets containing graded levels of protein, ranging from 37-62%. Maximum growth was found to occur at dietary protein levels ranging from 40-51%. The best food conversion ratio was achieved at 56% dietary protein and the best protein efficiency ratio was obtained at a dietary protein inclusion level of 37-40%. The protein to energy ratio was defined by feeding 3 different protein levels at 3 different P:E levels. These semi-purified diets contained 35, 45 or 55% protein and 6, 8 or 12% dietary lipid, resulting in protein to energy ratios ranging from 21.1 to 42.3mg/kJ. The optimal P:E ratio for this species was found to be 26.7mg/kJ. This diet effected a low food conversion ratio (1.72±0.19), a low hepatosomatic index (4.01±0.23) and a high specific growth rate (5.96±0.36). The essential amino acid requirements of juvenile P. commersonnii were investigated. Semi-purified diets were formulated to contain graded levels of crystalline lysine based on the amino acid profile of the whole body and fed to the fish for a period of 60 days. Fish fed the "ideal protein" diet had significantly higher (p<0.05) specific growth rates (2.95±0.18), protein efficiency ratios (0.41±0.05) and significantly lower (p<0.05) food conversion ratios (3.02±0.29). Lysine levels in the whole body increased with increasing levels of supplemented lysine. The dietary requirement of lysine was found to be 4.30% of dietary protein. The crude protein digestibility of six protein sources was investigated. Diets were prepared with 1% chromic oxide as an internal marker. The tested protein sources included low temperature Danish fishmeal, steam dried Chilean fishmeal, blood meal, carcass meal, defatted soyabean meal and Spirulina meal. These potential fishmeal substitutes were selected due to their favourable amino acid profiles, and in particular their high levels of lysine, and their high protein content. Both the animal and the plant protein sources were highly digestible. Digestibility co-efficients ranged from 66.09% for Spirulina meal to 73.38% for low temperature Danish fishmeal. The results have shown that juvenile spotted grunter require a minimum of 40% crude protein in their diet, a P:E ratio of 26.7mg/kJ and a lysine concentration of 4.30% of the dietary protein. Long term growth trials are needed to confirm these results. The hypothesis that the proximate composition of the natural diet, and the proximate composition of the animal under investigation, provides a reliable indication of the animals' nutritional requirements was shown to be valid. Differences between the predicted, and the empirically determined optimal protein and protein:energy ratios were slight.

This study aimed to expand the existing knowledge on the diversity and distribution patterns of intertidal fishes in the Sardinia Bay MPA and adjacent open access areas. It focussed particularly on in intertidal fish communities along the Agulhas Bioregion coast which has been understudied, especially in recent years. Typical resident species belonging to the family Clinidae were the most abundant, conforming to previous studies. Species from the family Gobiidae were the second most abundant in this study but this family was not previously recorded as being abundant. Transient species were unimportant in the current study which is in contrast to previous studies in the region and suggests a change in species composition. Certain transient species utilised intertidal rockpools as part of their nursery areas in the Eastern Cape, as has previously been found around Algoa Bay. A decrease in species richness from east to west was recorded in this study which has been noted by previous authors and the diversity and distribution patterns of the intertidal fish in the current study conformed to patterns found previously. The position of the biogeographic boundary between the Agulhas and Natal Bioregions could not be confirmed but Wavecrest (along the Transkei coastline) appeared to be part of a transition zone rather than a fixed break. More sampling around this area is recommended to determine the location and understand the dynamic nature of this boundary. The fish species were found to be vertically distributed across the shore with most of the resident species being more abundant across the low shore while the transient species were more abundant in the middle to low shore pools. This vertical distribution has been found at many sites around the world. The volume of the pools proved to be the primary controlling factor while the effect of temperature on vertical distribution could not be demonstrated. The benefits of the Sardinia Bay Marine Protected Area on this unexploited community of fishes could not be demonstrated but the long term benefit of protection has yet to be shown. Results from this study suggest that despite the correspondence with general biogeographic trends, the intertidal fish community has changed in composition (at least in terms of transient species) during the last 30 years and the cause for these changes may in part be reduced recruitment from exploited linefish.

Tests showed that, in Kamloops trout, Salmo gairdneri kamloops Jordan, egg number produced at spawning is dependent on egg size for fish of a given length. Mean egg size in trout from Paul lake was considerably smaller than that of Penask lake trout. The difference is associated with natural selection pressures of low and high population densities, respectively. Egg number was inversely correlated with egg size in all samples. Pew differences were found between age classes within the natural populations. Starvation during early ovarian maturation produced a reduction in numbers of eggs shed at spawning. Experimental starvation treatments of hatchery trout indicated that increasing degrees of starvation resulted in commensurately fewer eggs reaching maturity. Pull diet conditions for the remainder of maturation resulted in no compensatory change in egg size. Maturing ovaries and stomach content volumes from trout reared naturally indicated a positive correlation between reduced food intake and increased follicular degeneration. Variations in egg number are therefore attributable to differences in egg size, fish size and adequacy of food supply. Egg size is apparently genetically controlled. Direct reduction of fecundity by starvation has an adaptive value in partially limiting population density. / Science, Faculty of / Zoology, Department of / Graduate

The effects of temperature upon acetylcholinesterase (AChE) from the nervous system of fish were studied to determine if such compensatory phenomena as thermal accommodation, thermal acclimation and evolutionary adaptation to temperature as displayed by this physiological system could be observed and interpreted at the level of enzyme function. At probable physiological substrate concentrations the rate of acetylcholine (ACh) hydrolysis by AChE from rainbow trout (Salmo gairdnerii) and electric eel remains relatively unaffected by assay temperature over the temperature ranges normally experienced by these animals. Plots of Km versus temperature for these enzymes yield U shaped curves with minimum Km values occurring at temperatures close to the minimum habitat temperature. It is proposed that thermal accommodation of reaction rate is achieved throughout the habitat temperature range by temperature directed changes in enzyme-substrate affinity. Thermal acclimation in rainbow trout, and probably in speckled trout (Salvelinus fontinalis) and lake trout (Salvelinus namaychus) is accompanied by alterations in the relative proportions of two electrophoretically distinct AChE variants displaying different and adaptive Km-temperature relationships. Since the minimum Km values and energies of activation of the two rainbow trout enzymes are similar, and the specific activities of the enzymes are essentially identical following acclimation of fish to 2° and 17°C, it is suggested that rate compensation of AChE activity may not occur at different acclimation temperatures. However, the possibility remains that changes in such factors as pH, ionic environment and membrane lipids which accompany the acclimation process may act to stabilize reaction rates. Comparisons of AChE enzymes from rainbow trout, electric eel and the Antarctic fish Trematomus borchgrevinki indicate that the evolutionary adaptation of AChE function in species inhabiting different thermal environments is based upon selection for a Km-temperature relationship that will allow thermal accommodation of reaction rate over the temperature range normally encountered. Shifts in the Km-temperature relationship during speciation are interpreted in terms of changes in enzyme conformation following the accumulation of amino acid substitutions. Possible mechanisms by which two AChE enzymes could be incorporated into the trout central nervous system were considered and a hypothesis involving hybridization between fish populations was tested with trout inter-species crosses. It was observed that hybrids formed between speckled and lake trout contained a greater number of electrophoretically distinct AChE variants than did either parent and further, the presence of similar thermally controlled AChE complexes in rainbow, speckled and lake trout indicated that the original incorporation of multiple AChE enzymes into the rainbow trout probably occurred prior to the evolutionary divergence of these three species. It is concluded from this study that changes in enzyme-substrate affinity with temperature, and the temperature directed production of enzyme variants displaying adaptive Km-temperature relationships, are both important mechanisms for controlling catalytic activity in an enzyme system which functions over a wide range of temperatures. / Science, Faculty of / Zoology, Department of / Graduate

Laboratory experiments were conducted to study the effects of dehydro-abietic acid (DHA) on the physiology of the adaptation of sockeye salmon smolts (Oncorhynchus nerka) to sea water. Dehydroabietic acid occurs in the rosin of commercially important coniferous trees and is found in the untreated effluents of the pulp and paper industry at concentrations acutely toxic to salmonids. As this resin acid is known to be one of the more persistent toxic components of kraft mill effluent (KME) and although its concentrations are greatly reduced by biological treatment, DHA is nevertheless discharged in the effluents of the pulp mills situated on the Fraser River system as well as of those located on the coast of British Columbia. As sockeye salmon utilize both the Fraser and Thompson Rivers during their downstream migration, this species may be exposed to DHA before entering the sea. An attempt was made to simulate this situation in the laboratory by exposing sockeye salmon smolts to a sublethal concentration of DHA (0.65 mg/L) in fresh water for 120 h and then transferring them into sea water (28 °/oo) containing no DHA. Hydromineral balance was studied by monitoring changes in plasma osmolality, plasma NA⁺, K⁺ , Ca⁺⁺, Mg⁺⁺ and Cl⁻, blood hematocrit and muscle water content at the end of the freshwater DHA exposure and at 24 h intervals during the adaptation to sea water (120 h). After 24 h in sea water the gill permeability to water and the water transport ability of the gut were also determined. Supportive experiments measured changes in the size of red blood cells, the levels of plasma bilirubin as well as the uptake and tissue distribution of DHA in sockeye salmon smolts. Lipid extracts of various tissues were analyzed for DHA residues by gas chromatography coupled with mass spectrometry (GC-MS). The exposure of sockeye salmon to DHA in fresh water resulted in a hydromineral disturbance characterized by a drop in plasma osmolality, sodium, and chloride, indicating a general hydration which was reflected by increased muscle water content. A lowering of dissolved oxygen to 75% saturation markedly increased the toxicity of DHA and the osmotic imbalance may have been a secondary result of an adaptive respiratory response to a hypoxic stress brought on by DHA exposure. Increases in blood hematocrit were caused by a swelling of the red blood cells related to lowered plasma osmolality. When these fish were transferred to sea water, the hydration was replaced by dehydration and a rise in osmolality was caused by abnormally elevated levels of all the plasma ions. The added salinity stress resulted in some mortality and considerably greater excursions in plasma electrolytes occurred in fish which were experiencing locomotor difficulty. Plasma magnesium showed the greatest elevation and took the longest (96 h) to return to normal levels. Prior DHA exposure increased the permeability of the gill. During acute DHA exposure in fresh water a gradual deterioration in schooling and fright response was followed by hypersensitivity to mechanical stimuli and abnormal swimming behavior. After sublethal exposure, the reduction in schooling and fright response generally became most evident during the first 24 h of sea water adaptation. These results of the study are discussed in terms of the possible roles played by the gills, gut and kidney in the DHA-induced perturbations of hydromineral balance. The implications of the accompanying alterations in behavior are discussed in the context of the ecological survival of sockeye salmon smolts during adaptation to sea water. Residue analyses showed that sockeye salmon accumulated DHA from the water to high levels in the brain (954 x), liver (428 x) and kidney (404 x) as well as in other tissues. The presence of DHA metabolites in the bile, which also contained the highest DHA residues (647.3 μg/g), indicates that the hepatobiliary route is important in the excretion of DHA by fish. The possibility of the bioaccumulation of DHA by fish in the wild is discussed in relation to the setting of water quality criteria for pulp mill effluent. / Science, Faculty of / Zoology, Department of / Graduate

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