Thesis (M.Sc. (Aquaculture)) -- University of Limpopo, 2012 / The feeding habits of a macrophagous fish, Tilapia rendalli, were investigated at an oligotrophic dam that has no macrophytes, Flag Boshielo Dam. This dam supports a significant population of the macrophagous, Tilapia rendalli. The diet of T. rendalli was investigated by examining the frequency of occurrence of different food items in the stomach of the fish over a period of twelve months. A size related dietary shift was evident. The diet of juvenile fish (<5 cm) was dominated by zooplankton and the diet of adult fish (>15 cm) was predominantly marginal vegetation, particularly Cyperus sexangulasris and Panicum schinzi. However, dietary overlaps between the different size groups were evident. The diversity of food items increased with fish size until the fish were 15 cm in length and thereafter declined as the fish predominately fed on marginal vegetation. Scales were used to determine the age of T. rendalli. Age at length data was fitted to the Von Bertalanffy growth model, which showed that males grew faster and attained a larger size than females. The growth of T. rendalli in Flag Boshielo Dam was comparable to those reported in other dams with macrophytes. It is inferred here that the absence of macrophytes is not a limiting factor in the growth of T. rendalli in lentic ecosystems. The ability of T. rendalli to achieve good growth rates when feeding on marginal vegetation prompted a subsequent study where its utilisation of readily available plant diets was evaluated under culture conditions. The culture of macrophagous fish that naturally feed on plant diets may be the solution to reduce the current dependence on fishmeal. Fishmeal is not only expensive, but its supply is not always guaranteed. This study focussed on the growth performance, gastric evacuation rate, gastric transit time and carcass composition of Tilapia rendalli fed fresh plants, to determine the extent to which T. rendalli can utilise fresh plants. Kikuyu grass (Pennisetum clandestinum), cabbage (Brassica oleracea), duckweed (Lemna minor), vallisneria (Vallisneria aethiopica) and fishmeal pellets (control) were offered ad libitum to duplicate groups of T. rendalli for 224 days. Specific growth rate (SGR), protein efficiency ratio (PER) and food conversion ratio (FCR) were used to determine the growth performance. Fish fed kikuyu grass attained a significantly (P<0.05) higher SGR and a better FCR than those fed on the other plant diets. Fish fed vallisneria lost weight. The serial slaughter method showed that vallisneria was vii evacuated significantly (P<0.05, ANCOVA) faster and was eaten in significantly (P<0.05) higher quantities than the other diets. Kikuyu grass was evacuated much more slowly and eaten in lesser amounts than the other plant diets. The low energy content (14.74 MJ/kg) of vallisneria may explain its faster evacuation and high consumption levels. Digestibility studies indicated that T. rendalli is capable of breaking down both cellulose and fibre. Fish fed kikuyu grass had higher protein levels, higher omega-3 fatty acids (25.13%) and higher mineral content than those fed on the other experimental diets. Fishmeal fed fish had the lowest content of the omega-3 fatty acids (2.52%). T. rendalli performed better when fed plant diets with higher protein and energy contents. The good growth performance and carcass quality of T. rendalli fed on kikuyu grass, led to another study where the use of kikuyu grass meal as a dietary protein replacement for fishmeal in practical diets for T. rendalli was evaluated. To determine the optimum substitution level, kikuyu grass meal was used to replace 20, 40, 60 and 80% of fishmeal in isonitrogenous (CP =16.70%) and isocaloric (GE =15.20 MJ/kg) diets. The test diets were fed to triplicate groups of fish held in 1 m3 fibre glass tanks at 10 (36 ± 2 g) fish per tank for 60 days. The best specific growth rate (1.60 g/day) and feed conversion ratio (1.86) were recorded for fish fed diets with 20% kikuyu grass meal. The lowest specific growth rate (1.29 g/day) and feed conversion ratio (2.56) were recorded for fish fed diets with 80% kikuyu grass meal. When the level of kikuyu grass meal was more than 20% in the diet, growth performance was reduced. However, there were no statistically significant differences in the growth performance indices measured across the tested diets. The observed reduction in growth for diets containing higher kikuyu grass meal is explained by the decreasing amino acids levels (particularly methionine and lysine) and increasing fibre content. The results from the growth trials suggest that kikuyu grass meal is a suitable protein replacement for the expensive fishmeal in T. rendalli practical diets when it constitutes up to 20% of the dietary protein.

Mass transfer processes in food systems, such as solute infusion, are poorly understood because of their complex nature. Food systems contain porous matrices and a variety of continuous phases within cellular tissues. Mass transfer processes are generally not pure diffusion: often convection, binding and obstructing diffusion will occur. Monte Carlo (MC) simulation has been increasingly used in life science and engineering to elucidate molecular transport in biological systems. However, there are few articles available discussing MC simulation in food processing, especially mass transfer. The main goal of this study was to show the inherent simplicity of the MC approach and its potential when combined with traditional experimental and theoretical approaches to better describe and understand mass transfer processes. A basic framework for MC random walk - simulation applied to a diffusion problem - is developed in this project. Infusion of two sizes of dextran macromolecules in fish muscle cells is used to apply the MC framework in combination with Fluorescence Recovery After Photobleaching experiments. Effective diffusivity coefficients within cells, considering the degree of obstruction due to the myofibrilar matrix, are assessed. Then, the results are used as input in a mathematical model that was developed for theoretical simulation of mass transfer in the multi-cellular tissue. Diffusivity values obtained by the MC framework had an SD of ±0.02 [µm²/s] around the true value of 0.25 [µm²/s]. MC results for degree of obstruction were 0.29 and 0.34 for dextran FD1OS and FD2OS, respectively, and the Devalues were 23.7 and 11.2 [µm2/s]. The statistical error in the estimation of D was estimated to be [22.8-24.6] and [9.7-12.7] (95% CI), where average experimental values of 24.3 [µm²/s] for FD1OS and 11.4 [µm²/s] for FD2OS were captured by the respective interval. The theoretical model showed a significant influence of the cell membrane characteristics and tissue porosity in both the degree of solute penetration and the solute distribution between intra- and extra-cellular space. The combined approach was successfully applied to a diffusion problem. Overall, it is expected that the present work will contribute towards the application of MC simulation in the field of Food Science and Engineering. / Graduation date: 2006

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Intensive methods for the mass production of Oreochromis niloticus (Chitralada strain) seed using concrete tanks, hapas within earthen ponds and earthen ponds were investigated. On the basis of these trials, the productivity and economic performance of various production strategies for hormonally sex-reversed Oreochromis fry (MT fry) were then compared and modelled for adoption in Central and Northeast Thailand. Regular disturbance and harvesting of seed after a short period of spawning opportunity (5-10 days) was found to increase seed production in concrete spawning tanks. Exchange of female broodfish increased synchrony of breeding. A change in conditioning and spawning environment had no effect on seed yield from spawning tanks and hapas (area =12.57 m2and 40m2 respectively). Seed wet weight, seed clutch size and weight was greater in female fish spawned in tanks than hapas. Females conditioned in hapas however produced heavier seed clutches of larger absolute and relative size than tank conditioned fish. Records of tagged females indicated considerable differences in the frequency of spawning; in hapas the distribution was normal wheras in tanks it was skewed. The evidence suggests that hierarchy is important in the control of reproduction and exerts it's strongest effect in clear water, densely stocked tanks. Selective female broodfish exchange optimised seed yield per unit weight of broodfish and seed production was not improved by conditioning females for periods longer than 10 days. Male broodfish exchange did not significantly improve (P &gt; 0.05) seed yields. Early nutrition of broodfish raised under different supplemental feeding regimes in fertilised earthen ponds had a significant effect on later spawning frequency in concrete tanks. However, this effect was confined to broodfish maintained at densities lower or higher than optimal for seed production. Broodfish stocked over a range of densities for extended periods (201 days) showed greater variability of seed production in hapa than tank production systems. This was mainly due to periods of poor water quality in hapas; when water quality was high seed production was significantly higher in hapas than tanks over a range of broodfish densities. The optimal density of broodfish for seed production was exceeded in tanks but not hapas. The relationship between seed production and broodfish density over time suggested that both stocking biomass and number have an effect on fry output. Density of broodfish showed an inverse relationship to clutch size in both tanks and hapas and synchrony of spawning in tanks. Production of swim-up fry in large earthen ponds (area=1740m2) was not significantly different (P&gt;0.05) at 2 levels of harvest intensity. The use of small broodfish however produced double the yield of hormone treatable fry than a similar biomass of larger broodfish of the same cohort. A commercial scale incubation system was devised and evaluated in order to allow tank and hapa systems harvesting unhatched seed to be compared with the production of swim-up fry obtained from earthen ponds. Seed removed from mouthbrooding females was roughly staged and incubated in batches of similar development to give information on survival to swim-up fry. A simple incubation system was designed with a capacity for hatching &gt;100,000 eggs/set. A mean survival of 75% of all harvested seed to swim-up fry was obtained over several trials. A trend to intensification (fry/mVday) from ponds to hapas to tanks was evident when yields of swim-up fry are compared. Productivity exceeded any in the published literature for comparable systems, largely because of the intensity of broodstock management and early and efficient harvest of seed. Broodfish productivities (fry/kg female/month) were also higher across the range of systems tested often by a factor of 1.5-3. The best strategies were selected over a range of total investment cost using dominance analysis. Economic analysis suggested that for a start-up operation in Central Thailand fry production in earthen ponds can give the best return on levels of investment of less than Baht 0.8 million. Substitution of techniques into current carp fry production operations in Northeast Thailand indicated that more intensive methods (production in tanks and hapas) are more attractive over a range of investment levels. The break-even price of MT fry after hormone treatment in nylon hapas was approximately half the cost of treatment in a recirculated water concrete tank system. The break-even price in Central Thailand was lower than the Northeast by a factor of around 1.5 but the break-even price for both areas was lower than the current price of untreated Oreochromis fry.

Epidemiological studies have suggested that the consumption of fish may reduce the risk of cardiovascular disease. Compared to the number of studies using fish oils, few studies have used fish itself. Those which have used fish have generally used fattier fish such as mackerel and salmon as part of an uncontrolled diet. In this study, 23 healthy men consumed 200g each of Chinook salmon, Dover sole, and sablefish in a three-way crossover design for 18-day periods with three-week washout periods in between. The diets had the approximate composition of the 'Western' diet: 45% carbohydrates, 36% fat, and 16% protein with the sole diet containing 1.95 g omega-3 (n-3) fatty acids, the salmon diet 3.99 g n-3, and the sablefish diet 3.42 g n-3 fatty acids. Serum total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglycerides (TG), bleeding time (BT), blood pressure (BP), platelet aggregation (PA) using ADP and collagen as agonists, platelet fatty acid profiles (FAP), thromboxane B2 (TXB2) , and apolipoprotein B (Apo B) were measured at the beginning and end of each period. TC, and HDL-C, and TG changed significantly when compared to the prefish diet while both LDL-C and apo B demonstrated diet effect. LDL-C increased on both the salmon and sablefish diets (p = 0.08) compared to the sole diet, and increased approximately 15% on the former two diets compared to the prefish diet. Bleeding time was significantly longer when the salmon diet was consumed (p = 0.06). The impact of the three diets on PA depended upon the agonist. With collagen, only the sablefish diet decreased aggregation compared to the prefish diet. When ADP was used, aggregation decreased on both the fattier fish diets compared to the low fat fish (sole). Similar results were demonstrated for TXB₂: the fattier fish produced statistically equivalent decreases (p = 0.06) among the diets, and lowered TXB₂ compared to the prefish diet. There were no significant differences among the diets for either systolic or diastolic BP though there was a significant decrease (p = 0.01) in diastolic pressure compared to the prefish diet when the salmon diet was consumed. Platelet fatty acid profiles reflected diet composition. / Graduation date: 1993

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (MScFoodSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The preservation of various fresh fish products is achieved by either smoking, salting, canning, freezing or fermenting a highly perishable raw product. Since many of these facilities are not readily available, the use of fermentation as a means of preserving the product has been extensively practiced. However, the fermentation of fish is a time consuming practise and only by accelerating the process would it be possible to ensure the production of a more cost effective and readily available safe end-product. The quality of the fermented fish product is partially determined by the fermentation conditions and the metabolic activity of the microbes present. The rapid identification of the microbes present during the fermentation would enable the selection of possible starters to ensure an accelerated production of high quality fermented fish products. This study was thus undertaken to develop identification fingerprints for bacteria isolated from fermented fish products. A 1300 bp fragment of the 16S rRNA genes of each of the bacteria previously isolated was successfully amplified using the PCR technique. The isolates included strains of the genera Bacillus, Staphylococcus, Sphingomonas, Kocuria, Brevibacillus, Cryseomonas, Vibrio, Stenotrophomonas and Agrobacterium. The data obtained can, therefore, be used in the identification of these microbes isolated from other similar fermented fish products. The fingerprints could also be used to assist in determining the dominant microbial populations responsible for the characteristic qualitative changes occurring in the fish product during fermentation. The microbial composition of a fermenting fish product partially determines the quality of the end-product, therefore, the use of selected bacterial starters could result in the accelerated production of a microbial safe fermented fish product. A further objective of this study was to accelerate the production of a fermented fish product by inoculating macerated trout with either selected lactic acid bacteria (LAB) or with selected bacteria with high proteolytic activity over a 30 day fermentation period. The LAB included a combination of Lactobacillus plantarum, Lactococcus diacetylactis and Pediococcus cerevisiae strains, whereas the bacteria with high proteolytic activity included strains of Kocuria varians, Bacillus subtilis, two strains of B. amyloliquefaciens and a combination of these bacterial species. The quality of the fermented product was determined using changes in product pH, titratable acidity (%TA) and free amino nitrogen (FAN) formation as efficiency parameters. The data obtained during the fermentation of the macerated trout showed that the selected starters did not have a significant effect on the pH decrease in the product over a 30 day fermentation period. The LAB strains did not have a significant effect on the %TA of the fermenting fish product, yet the presence of these bacteria appeared to limit the FAN production in the product. The bacteria with high proteolytic activity resulted in slightly enhanced %TA values and a higher FAN content in the fermented product. It was also determined that the LAB and Kocuria varians, in contrast to the Bacillus spp. inoculums, did not survive the fermentation conditions well, possibly due to the low pH environment. The presence of the starter bacteria in the fermenting fish mixture at the end of the fermentation was also successfully determined with the use of the PCR-RFLP technique. The fermented fish product, obtained at the end of the fermentation period, had a good aroma and compared favourably to similar commercially available fermented fish products. The use of different microbial starters could in future enable the production of a diverse range of high quality products, which could be produced and marketed locally. / AFRIKAANSE OPSOMMING: Die preservering van ‘n verskeidenheid vars vis produkte word bereik deur die hoogs bederfbare produk te rook, te sout, te blik, te vries of te fermenteer. Aangesien baie van hierdie fasiliteite nie geredelik beskikbaar is nie, is die gebruik van fermentasie as ‘n preserverings metode al ekstensief beoefen. Die fermentasie van vis is egter 'n tydsame proses en slegs deur die versnelling van die proses sal dit moontlik wees om die produksie van ‘n meer koste effektiewe en geredelike beskikbare veilige eindproduk te verseker. Die kwaliteit van die gefermenteerde vis produk word gedeeltelik bepaal deur die fermentasie kondisies en die metaboliese aktiwiteit van die mikrobes teenwoordig. Die vinnige identifikasie van die mikrobes teenwoordig gedurende die fermentasie sal die seleksie van moontlike suursels om die versnelde produksie van hoë kwaliteit gefermenteerde vis produkte moontlik maak. Hierdie studie is dus onderneem om identifikasie vingerafdrukke vir bakteriee wat gei'soleer is van gefermenteerde vis produkte moontlik te maak. ‘n 1300 bp fragment van die 16S rRNA gene van elkeen van die bakteriee wat voorheen gei'soleer is, is suksesvol geamplifiseer deur die PCR tegniek. Die isolate sluit in stamme van die genera Bacillus, Staphylococcus, Sphingomonas, Kocuria, Brevibacillus, Cryseomonas, Vibrio, Stenotrophomonas en Agrobacterium. Die data kan dus gebruik word in die identifikasie van hierdie mikrobes as dit gei'soleer word van ander gefermenteerde vis produkte. Die vingerafdrukke kan ook gebruik word om die dominante mikrobiese populasies wat verantwoordelik is vir die kenmerklike kwalitatiewe veranderinge wat plaasvind in die vis produk gedurende die fermentasie, te identifiseer. Die mikrobiese samestelling van ‘n fermenterende vis produk bepaal gedeeltelik die kwaliteit van die eindproduk, daarom kan die gebruik van geselekteerde bakteriese suursels die versnelde produksie van ‘n mikrobies veilige gefermenteerde vis produk teweeg bring. ‘n Verdere doel van hierdie studie was om die produksie van ‘n gefermenteerde vis produk te versnel deur fyngemaakte forel met of geselekteerde melksuurbakteriee of met geselekteerde bakteriee met hoë proteolitiese aktiwiteit te inokuleer oor ‘n 30 dag fermentasie periode. Die melksuurbakteriee het ingesluit ‘n kombinasie van Lactobacillus plantarum, Lactococcus diacetylactis en Pediococcus cerevisiae, terwyl die bakterieë met hoë proteolitiese aktiwiteit stamme van Kocuria varians, Bacillus subtilis, twee stamme van Bacillus amyloliquefaciens en ‘n kombinasie van hierdie bakteriese stamme ingesluit het. Die kwaliteit van die gefermenteerde produk is bepaal deur die veranderinge in die pH, titreerbare suur (%TS) en vrye amino stikstof (VAS) vorming van die produk as effektiwiteits parameters te gebruik. Die data wat verkry is gedurende die fermentasie van die fyngemaakte forel het gedui daarop dat die geselekteerde suursels nie ‘n merkwaardige effek op die afname in pH in die produk oor ‘n 30 dag fermentasie periode het nie. Die melksuurbakteriee het nie ‘n merkwaardige effek op die %TS van die gefermenteerde vis produk gehad nie, terwyl dit geblyk het dat die teenwoordigheid van hierdie bakterieë die produksie van VAS in die produk belemmer het. Die bakteriee met hoe proteolitiese aktiwiteit het ‘n effense verhoogde %TS en ‘n hoër VAS inhoud in die gefermenteerde produk veroorsaak. Dit is ook bepaal dat die melksuurbakteriee en Kocuria varians, in teenstelling met die Bacillus spp. inokulums, nie die fermentasie kondisies goed oorleef het nie, moontlik as gevolg van die lae pH omgewing. Die teenwoordigheid van die suursel bakteriee in die fermenterende vis mengsel aan die einde van die fermentasie is ook suksesvol bepaal met die PKR-RFLP tegniek. Die gefermenteerde vis produk, verkry aan die einde van die fermentasie periode, het ‘n goeie aroma gehad en het goed vergelyk met soortgelyke kommersieel beskikbare gefermenteerde vis produkte. Die gebruik van verskillende mikrobiese suursels kan in die toekoms die produksie van ‘n diverse reeks hoë kwaliteit produkte wat plaaslik geproduseer en bemark kan word moontlik maak.

No description available.

Thesis (M. Sc. (Agriculture)) -- University of Limpopo, 2016 / Fish assemblages in relation to environmental variables within the Broederstroom and Debengeni Rivers were investigated. Both rivers were characterized by coarse substrates (pebble and gravel), temperatures below 20°C and moderate depth. Trout dominated fish assemblages in terms of numbers caught and was only distributed at higher altitude sites >1400 m (a.s.l). Coarse substrates, temperatures below 15°C, flow rate, depth and riparian cover were the variables shown important for the distribution of trout by multivariate analysis. The confinement of the trout to higher altitude and lack of optimal habitat variables at lower altitude sites contributed to the assertion that the area is marginal for trout distribution. It was therefore inferred that the marginality of the area is the possible explanation for trout failure to self-sustain its population, therefore dependent on the continuous restocks by the local hatchery. The continuous restocks of small size trout in the Broederstroom River prompted a subsequent study where trout’s impact on macroinvertebrate communities was evaluated through surveys and field experiments. The ability of small trout to utilize macroinvertebrates made them suitable candidates to evaluating their impact in the area. Aquatic invertebrates were found to be the main food source for the trout in the area. Taxa such as Gomphidae and Potamonautidae were the most frequent food items from the analyzed stomachs of trout. However, observations from both field surveys and experiments showed that trout is a weak regulator of macroinvertebrate diversity in the area, since there were no significant differences (ANOVA, P<0.05) in the diversity of invertebrates from trout invaded and uninvaded sites. Trout being a weak regulator of macroinvertebrate diversity in the area, it prompted surveys to the Ebenezer Dam to determine its competitive interactions with native predatory species. If the introduced species is a more efficient predator than the native predator species, it may affect changes in the structure of the habitat and food resource. Trout in the Ebenezer Dam was found to be selective to habitat variables whilst C. gariepinus was cosmopolitan to all habitat categories. The catfish also had a broader food preference than trout and the diversity of the food items was significantly different (ANOVA, P<0.05) between the two species. Unfortunately, the interspecific food overlap between trout and the catfish could not be determined in Ebenezer Dam, because of the small sample size of trout but food selection between vii them was evident. It was then concluded that the native catfish has a wider niche and it is a more efficient predator than the introduced trout. This observation contributed further to the assertion that the area is marginal for trout to thrive. Due to trout selection of habitat variables, it became prudent to carry out another study where the past climate and land use changes were analyzed to determine their effect on the habitat that could have affected the distribution of trout in the area. Future projections were also made to determine possible future impacts of climate change on the distribution of trout in the area. The effects of climate and land use change resulted in warmer water temperature, altered riparian cover and altered stream flow patterns. The changes could have influenced the confinement of trout to higher altitude catchments. The projected maximum temperatures by 2050 shows an increase from 2014 with a decline in precipitation. If these projections are to be the same for water temperature and flow regimes, coupled with current land uses in the area, they will continue to affect the distribution of trout negatively.