This study aimed to investigate the feeding behaviour of the calanoid copepod, Pseudodiaptomus hessei, particularly whether it prefers to feed on a planktonic or benthic food source. The effect of different microalgae species on the feeding preference, ingestion, and gut evacuation rate were investigated. Two microalgae species (Isochrysis galbana and Tetraselmis suecica) were used, to test gut fullness and gut evacuation of P. hessei. The copepods were starved for 6 h and allowed to feed on monalgae diets, I .galbana and T. suecica, and a 1:1 binary diet mixture of T. suecica and I. galbana. The gut fullness and gut evacuation rates were determined by observing under the dissecting microscope and gut content percentage was recorded (as 0, 25, 50, 75 or 100 percent) along with copepod sex. Copepods that feed on T. suecica fill their gut after 30 min, while those that feed on I. galbana do so after 40 min. There was a significant difference (p= 0.02) between sexes with males filling their gut faster than females. However, copepods that fed on I. galbana evacuated their gut content completely after 30 min, while those fed on T suecica evacuated theirs after 40 min. There was no difference between males and females for gut evacuation. Even though there was high gut fullness rate when P. hessei was feeding on T. suecica, I. galbana is recommended as the best mono-algae diet to culture P. hessei. The feeding behaviour of P. hessei was investigated, as to whether it prefers to feed on a planktonic or benthic food source. Copepods were starved for 3 h and then allowed to feed on two microalgae species (I. galbana and T. suecica), one presented as a benthic and other as planktonic. Controls included swapping the modes of presentation for each algae species. Ingested microalgae species were quantified using real-time PCR, with threshold cycles interpreted as relative abundance ratio (planktonic microalgae divided by benthic microalgae species). Pseudodiaptomus hessei preferred to feed on planktonic food sources initially as there was a difference between planktonic and benthic ingested food (p=0.026). Copepods shifted from planktonic to benthic food sources after 80 min of feeding planktonically. Planktonic food sources were the preferred choice for P. hessei regardless of microalgae species offered. The results from this study also confirm that P. hessei feed on a benthic food source during the day under culture conditions. This information can be used as baseline information for aquaculturists to rear the species as live feed for marine fish larvae.

M.Sc. (Zoology) / Please refer to full text to view abstract

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 biotechnology of production and utilisation of the cyanobacterium Spirulina has been well documented. Research has centred mainly on application in human and animal nutrition, and has been motivated by the high protein, vitamin, fatty acid and growth factor contents. The main obstacle in realising the full potential of this feed source has been the high production costs associated with its mass culture in defined media. The observation of blooms of Spirulina in tannery effluent evaporation ponds in Wellington, South Africa, prompted this investigation into the harvesting, and nutritional and toxicological evaluation of this potentially low-cost production system, with the ultimate aim of using the product in aquaculture rations. An investigation of the chemical gradient along the evaporation cascade showed a positive correlation between the prevailing chemical conditions and the dominant species populations. A standing crop of 9.5 tonnes/ha of Spirulina was found to be present in the latter alkaline ponds, characterised by relatively lower organic and sulphur contents. Initial harvesting of the biomass was achieved by the design, construction and implementation of a small-scale screen harvest, which yielded a 25 kg (dry weight) crop. A scale-up model was then designed, and implemented in a technical scale harvest, yielding a crop of 250 kg (dry weight). Both these harvests utilised the bloom of surface-autoflocculated biomass. Concentrated cell slurries were sun-dried on muslin beds, and milled to a coarse powder. An evaluation of the harvest revealed a chemical content similar to other published reports of defined media cultures, with the exception of the protein and amino acid contents. The observed lower levels of the latter two are almost certainly due to the sun-drying method employed, known to reduce the protein content due to thermal denaturation. Legislation demands the strict toxicological evaluation of new protein sources, and because of the effluent-nature of the growth medium of this source of Spirulina, its viability lies only in the application as an animal feed or supplement. A range of toxicological tests were chosen that were targeted to elucidate the possible toxicological constraints of this effluentgrown source of protein in animal nutrition. The nucleic acid and pesticide contents of the harvested biomass were within the prescribed safety ranges. Atomic absorption showed minimal accumulation of minerals and heavy metals from the effluent. A bioassay with the brine shrimp Anemia salina showed that the biomass contained no toxicologically active water-soluble components. A short term feeding trial with new-born chicks showed that supplementation with Spirulina had no effect on the growth rates and feed conversion ratios of the different feeding groups. Pathological analyses showed that the liver was the only target organ to elicit a change in response to supplementation of the diets with Spirulina. A general decrease in liver weight was noted, with Cu, Ca, Fe and Zn being significantly accumulated. A histopathological examination however, showed no cellular and functional aberration from the control animals. The toxicological analyses gave the preliminary safe go-ahead for the evaluation of effluent-grown Spirulina in aquaculture nutrition. The South African abalone Haliotis midae, and the rainbow trout Oncorhynchus mykiss were chosen as representative species of edible cultured organisms. The technology for the culture of the perlemoen abalone is being established in South Africa, with the main area of research being the development of an artificial diet for high density culture. A 40 day growth trial demonstrated that lower concentrations of Spirulina supplemented to an agar-based fishmeal diet resulted in growth rates and feed conversion ratios similar to the control fishmeal and purified-casein diets, and thus has application potential in the nutrition of this high-cost marine delicacy. The aquaculture technology of freshwater rainbow trout is already well established. An eight week feeding trial with various concentrations of Spirulina showed that this effluent-grown protein source can partially replace fishmeal in semi-purified diets. Fish fed Spirulina did not exhibit decisive manifestations of toxicity, as determined in a histopathological study. In addition, Spirulina supplementation resulted in enhanced colouration of the skin and flesh, which may have implications in the aesthetic marketing of this sought-after table fish. The primary aim of this preliminary investigation thus concerned the determination of the biotechnological potential of this effluent-source of Spirulina. A technology transfer from the economically unfeasible defined-media culture was implemented. This project is ultimately aimed as a contribution towards the treatment of tannery wastewater, by the removal of contaminants from the effluent in the form of organic biomass.

The gammarid amphipod Eogammarus confervicolus (Stimpson) was investigated as a potential mass culture organism, with utility as a diet supplement for artificially reared fish. Suitable conditions for large-scale culture were determined in a series of experiments. E. confervicolus demonstrated wide salinity and temperature tolerances, with best survival at low salinities (5 - 10⁰/00) and temperatures (5⁰ - 10⁰C). Population densities greater than 2 mg/1 reduced amphipod growth and survival, although densities may be increased with a flow-through system. E. confervicolus showed good growth and survival on a variety of algae and associated epiphytes, demonstrating the broad diet of the species. Clumping diatoms or phytodetritus were suggested as suitable foods for mass culture. Maintenance of populations over three generations showed the feasibility of long term culture of this amphipod. Short term growth rates of juvenile coho at 12°C were similar on live amphipods (3.2%/day), freeze-dried amphipods (2.4%/day) and Oregon Moist Pellets (3.1%/day). Protein analysis showed E. confervicolus to have a well-balanced amino acid spectrum, and proximate analysis indicated that the amphipod was a nutritionally satisfactory component of fish diets. A Leslie matrix model was developed from information about growth, mortality and fecundity of Eogammarus confervicolus under optimal conditions, and was used to test various harvest strategies. Highest yield of the strategies examined was produced by a weekly 41% harvest applied to amphipods between 0.6 and 2.2 mg dry weight. Further experiments testing the predictions of the Leslie matrix model were recommended. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

No description available.

A series of five experiments were carried out to determine the effect of supplementary enzymes on growth performance and feed utilisation of juvenile gilthead sea bream, Sparus aurata, fed diets in which soybean meal (S8M) partially replaced fish meal (FM). In the first of these experiments the addition of cocktails containing 1 g/kg low pH active protease and 1 glkg a-galactosidase or 1 glkg high pH active protease and ] glkg a.-galactosidase to a 320 glkg SBM, 260 glkg FM pressed diet were both found to significantly (P<0.05) improve performance of fish fed these diets compared to fish fed the unsupplemented diet and a 320 glkg FM, 220 glkg SBM diet. This improvement in performance was not obtained when fish were fed 440 glkg SBM, 230 glkg FM diets with the same enzyme combinations. In some parameters performance of fish decreased as the SBM level in the diets was increased. The significant improvements observed in Experiment 1, with addition of enzyme cocktails to the 320 glkg S8M diet, were not repeated in any of the subsequent experiments. The second experiment was aborted due to ahnormal feeding hehaviour of the fish. In the third experiment, in which the enzymes employed in Experiment 1 were used individually at 1 glkg in 320 glkg SBM diets, no significant differences in specific growth rate (SGR), food conversion ratio (FeR) or protein efficiency ratio (PER) were noted in comparison to fish fed the unsupplemented diet. This was also the case with fish fed diets to which the two enzyme cocktails had been added at enzyme inclusion levels of 0.5 glkg each. Although no significant differences were found, feeding the diet with low pH protease alone appeared to increase performance compared to fish fed the unsupplemented diet, and the results of fish fed diets with high pH protease alone or with a.-galactosidase alone indicated that there was a decrease in performance compared to fish fed the unsupplemented diet. In Experiment 4 fish fed 320 g/kg SBM diets with 0.5, 1.0 and 1.5 g/kg low pH protease showed similar SGRs, FCRs and PERs which appeared to show an improved performance (although not significantly so) compared to fish fed diets with 1.0 glkg agalactosidase used together with either 0.5 or 1.0 glkg low pH protease. In the fmal experiment fish were fed 320 g/kg SBM extruded diets to which 0, 0.33, 0.66, 1.00 and 1.33 glkg of low pH protease had been added. Although no significant differences in SGR, FCR or PER were obtained, fish fed the diets containing 0.66 and 1.33 glkg protease appeared to improve performance compared to fish fed any of the other diets or a diet containing 320 glkg FM and 220 glkg SBM. Fish fed the other 320 glkg SBM supplemented dietc; gave similar results. A histological study of the position of nuclei in hepatocytes and the presence of fat globules around hepatopancreatic tissue in liver samples taken from fish fed the various experimental diets failed to show any relationships with either SBM level or enzyme inclusion in the diet. A series of analyses on the distribution of activities of six enzymes in the digestive tract of sea bream indicated that relative activities differed from one enzyme to another and from one region to another. In an investigation into the variation of pH in various parts of the digestive tract after one or two feeds, it was observed that within the first 24 hours after feeding the pH in the stomach decreased to a minimum value of 2.5 and the pH in the rest of the intestine varied between 6.5 and 7.7. vi From a series of gastric evacuation trials which were performed, it was found that the time of day sea bream were fed a meal influenced the gastric evacuation rate, with fish fed in the afternoon taking longer to evacuate the meal than fish fed a similar meal in the morning. Doubling the size of a meal did not double the gastric evacuation time. Instead, the time to evacuate a given percentage of the larger meal only increased by 1.4 and 1.6 times in fish fed the pressed and extruded feeds respectively compared to fish fed the smaller meal. When the sea bream were fed multiple meals it was found that the evacuation rate of an earlier meal was increased by a subsequent meal. A series of trials investigating the distribution in consumption of a population of sea bream fed a single meal indicated that there was a wide variation in the amount of food consumed by each fish in the population and it was observed that even fish of the same size consumed very different quantities of food. Before any definite conclusions can be drawn regarding the use of the three enzymes tested in these experiments to improve growth and feed utilisation in FM-substituted diets, further investigations need to be carried out in an attempt to obtain more significant results. This thesis has shown that additional research into the mode of action of these enzymes is required as well as studies into how the digestive physiology of the sea bream may affect the use of these (and other) supplementary enzymes.

The nutritional suitability of some Bangladeshi oilseed by-products (mustard, Brassica juncea; linseed, Linum usitatissimum; sesame, Sesamum indicum) as fish meal substitutes in carp diets was investigated. These protein sources were shown to cause depressed growth and feed efficiency when substituting 25% or more of the fish meal protein in semi-purified diets. However, the use of these oilseed meals in combination was found to be more effective than that of single sources. Supplementation of plant protein diets with crystalline EAA improved their nutritive value. Growth performance was better in fish fed diets supplemented with all deficient EAA than in fish fed diets supplemented with the first limiting EAA. Nutrient digestibility studies with these plant proteins suggested reasonable agreement between apparent protein digestibility (APD) and average apparent amino acid digestibility (AAAD). APD and AAAD values ranged from 78.9% to 85% and 82.4% to 85.8% respectively. Both aqueous and enzyme treatments were effective in reducing (49% and 57% respectively) the anti-nutritional factors (e. g. allyl isothiocyanate) in mustard oilcake. In linseed and sesame meals heat treatment was the most effective (reducing phytic acid levels by 72% and 74% respectively). Use of detoxified meals in diets improved growth performance and food utilization compared to untreated meals. Dietary phytic acid in the presence of increased levels of calcium and magnesium significantly (p &lt; 0.05) depressed growth, food utilization and mineral bioavailability (especially Ca and Zn) in carp. Carp were shown to be tolerant of a dietary glucosinolate (allyl isothiocyante) level of 0.4 mg glucosinolate/g diet without inhibiting growth performance or adverse effects on fish health. However, fish fed diets containing higher levels of mustard oilcake or allyl isothiocyanate showed abnormal changes in thyroid tissues. The results of this study are discussed in relation to previously published research on fish and other monogastric animals.

In Thailand, culture and production of a high value freshwater fish, the marble goby, is dependant upon farm-made feeds using marine and freshwater trash fish as primary ingredients. However, there is lack of nutritional research regarding the use of such farm-made feeds and their impacts on the nutritional status, growth and health of marble goby. The aims of the present study were to evaluate the effects of farm- made feeds on slaughter indices, fish lipid classes and fatty acid profiles, nutrient composition and digestibility. In addition it was intended to improve on-farm feed quality for both current practical feeds as used by farmers and alternative feeds using rice bran and tilapia with reference to biochemical composition, growth performance and haematology of marble goby. Nutritional evaluation of farmed fish compared to their wild counterparts indicated that fatty acid composition of farmed marble goby was markedly influenced by diet. Marble goby appeared to utilize MUFA preferentially as an energy source compared to SFA. Fish muscle was characterised by higher n-6 PUFA; arachidonic acid (20:4n-6, AA) and docosapentaenoic acid (22:5n-6, DPA). Eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22: 6n-3, DHA) comprised the majority of n-3 PUFA found in fish muscle and can potentially be enriched into marble goby muscle through the diet. The significantly higher ratios of neutral liver lipid to polar lipid (NL/PL) indicated the imbalance of dietary lipid and energy of on-farm feeds. Moreover, findings on slaughter indices and lipid peroxidation of farmed fish; higher HSI, VSI, liver TBARS and the pale lipid-rich liver of farmed fish indicated problems with the nutritional quality of lipid in farm-made feeds. Experiments aimed to improve farm-made feeds using supplemental vitamin E in the form of α-tocopherol. These demonstrated that supplementation of α-tocopherol to oxidised diets, both mackerel and tilapia based, did not result in a significant beneficial effect in reducing mortality, and improving growth and haematology in marble goby. However, dietary α-tocopherol supplementation helped in reducing fish muscle peroxidation but was not related to muscle α-tocopherol levels. In mackerel based diets containing lipid peroxidation up to 250-300 µmols MDA g-1, α-tocopherol supplementation appeared not to help in reducing liver peroxidation. The alternative use of tilapia as a feed for marble goby resulted in growth and survival rates similar to those of fish fed mackerel based diets. Tilapia contained intrinsic α-tocopherol levels that appeared to be sufficient to reduce marble goby tissue peroxidation. The synergic effects on antioxidant activities between α- tocopherol supplement and natural E vitamer contained in rice bran helped to reduce tissue TBARS and improve haematology in fish fed combination diets of oxidised tilapia and rice bran. The inclusion of rice bran in farm based diets resulted in decreased tissue peroxidation, an adverse affect on dry matter and protein digestibility; and lower fish feed intake, growth and survival rate when 25% of rice bran was added into practical mackerel based diet. Overall, formulated feeds showed promising growth and survival rate in marble goby but more research on dietary nutrients and energy balances are required.