Department of Animal Sciences

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Application of the condition factor in the production of African sharptooth catfish Clarias gariepinus
(Stellenbosch : University of Stellenbosch, 2005-03) Luckhoff, Paul Daniel; De Wet, Lourens; Brink, Danie; University of Stellenbosch. Faculty of AgriSciences. Dept. of Animal Sciences.
In recent years there has been a renewed interest in the commercial culture of African Sharptooth Catfish. Its robust characteristics and its air breathing capabilities makes the African catfish a good candidate for culture in intensive recirculating systems. In light of the size variation in offspring spawned from undomesticated fish, that may eventually increase cannibalism, suitable methods for the quantification of some production performance parameters such as growth and health measurements need to be established for application in intensive catfish culture. In fish the condition factor (CF) reflects information on the physiological state of the fish in relation to its welfare. This factor is expressed as Fulton’s condition index, or the K-factor. African Sharptooth Catfish fry with average weight of 1.9g ± 0.7867 and average length of 59.375mm ±8.812 were equally allocated into ten 1000L-recirculating tanks. The fish were fed a commercial feed to apparent saturation at a frequency of 5 times per day. Sixteen fish were sampled out of each treatment. Weight (g) and length (mm) of each fish were recorded every seven days over a trial period of 175 days from which Fulton’s condition index K was calculated. Results were analysed for significant differences using one-way ANOVA and Tukey’s pair wise comparison test for the various parameters. Growth parameters (a = -5.083, b = 3.004, R2 = 99.4%) derived from the logarithmic relationship between body weight (W) and standard length (L) indicated an isometric growth through the duration of the trail. No significant differences (P>0.05) in condition factors between treatments were found at the beginning of the trail. Significant differences (P<0.05) were found at the end of the trail for weight between ponds and condition factor between treatments. No significant difference (P> 0.05) between length and treatments were found at the end of the trial. Mean condition factor was 0.856 ± 0.187. By using this information on condition factor for African catfish a K-factor calculation chart for African catfish could be calculated, to be used as a practical measurement tool to measure performance goals on catfish farms.
Aquaculture practices in irrigation reservoirs of the Western Cape Province of South Africa in relation to multiple resource use and socio-ecological interaction
(Stellenbosch : Stellenbosch University, 2014-04) Salie, Khalid; Rana, Krishen; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Aquaculture has proven to be a viable operation in multi-used irrigation reservoirs (also referred to as farm dams) in the Western Cape province (WCP) of South Africa. Many studies found that the fitness-for-use of these reservoirs for both net cage culture of fish and irrigation of crops is feasible. However, practising intensive fish farming in existing open water bodies can increase the nutrient levels of the water through organic loading, originating from uneaten feeds and fish metabolic wastes. Under such conditions the primary (irrigation) and secondary (drinking water and recreation) usage of the dam could be compromised by deteriorating water quality. Rainbow trout (Oncorhynchus mykiss) farming is done in Mediterranean climatic conditions of the WCP. This type of climate presents short production seasons with fluctuating water quality and quantity. The study investigated the dynamics of water physico-chemical parameters and assessed the long term impact of rainbow trout farming on irrigation reservoirs. Furthermore, associated land-use in the catchment of such integrated aqua-agriculture systems is described, and mitigation to minimise the impact of fish farming evaluated. The investigation concluded with assessing the contribution of aquaculture to rural and peri-urban communities. The aim is to present an integrated, socio-ecologically balanced farming system for irrigation reservoirs with associated aquaculture activities. A total of 35 reservoirs, including both fish farming and non-fish farming ones, were selected as research sites. They were located in three geographical regions namely, Overberg (Grabouw/Caledon), Boland (Stellenbosch/Franschhoek) and Breede River (Ceres/Worcester). Reservoirs were <20 ha in surface area and the volume ranges from 300 000 to 1 500 000 m3. Water samples were collected monthly and seasonally for the different investigations and analysed for a range of water quality parameters, including: transparency (Secchi disc), temperature, dissolved oxygen (DO), pH, sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), chloride (Cl), carbonate (CO3), bicarbonate (HCO3), manganese (Mn), copper (Cu), zinc (Zn), boron (B), total phosphorous (TP), orthophosphate (PO4), total ammonia nitrogen (TAN), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), aluminium (Al), total suspended solids (TSS), total dissolved solids (TDS), alkalinity, hardness and sulphate. Phytoplankton samples were also collected, genera identified and biomass calculated. The water quality data were analysed in terms of surface and bottom strata in both fish farming and non-fish farming reservoirs based on repeated measurements at the same site location at different times using the procedure General Linear Models of Stastical Analysis System (SAS, 2012). Values p<0.05 were considered as statistically significant. A Principal Component Analysis (PCA) biplot was used to graphically depict all the sites and measured water quality variables with the purpose of trying to see whether the fish farming and non-fish farming ones showed any groupings and how the sites were related to the measured variables. Structured questionnaires and informal discussions were used to collect additional information on the water use, production data and socio-economic effects on fish farmers. Categorical data gathered from the interviews (21 aquaculture projects) were analysed for frequency of occurrence using the Statistical Product and Service Solutions (SPSS) computer programme (SPSS Systems for Windows, Version 12.0). Results are presented in publication form with research chapters focusing on the subject areas of water quality impact, catchment land-use, potential mitigation measures and aquaculture contribution. Results for the water quality analyses indicated that as a collective, the farm reservoirs’ overall minimum, mean and maximum values for the physico-chemical parameters were fit-for-use for trout farming. The depth of the reservoirs ranged from 1.2 - 21.6 m with the low value taken during the summer season. Values lower than 5.0 m can cause management problems for floating cages that require a minimum of 4.0 m for net suspension and 1.0 m of free space below for adequate lateral flow. The Secchi disc reading of the reservoirs ranged from 10 – 510 cm. Higher transparencies were recorded after the winter rains when sand, silt and clay settled. Trout feeding is dependent on visibility and transparencies of more than 50 cm are required for good feeding conditions. The dissolved oxygen (DO) ranged from 0.3 – 16.4 mg/L with values below 5.00 mg/L recorded during summer when extraction and temperatures were high and provided conditions unable to sustain trout farming. The situation reverses with the onset of winter when the dams fill and DO rises above 5.00 mg/L as required for trout farming. The phosphorous (P) levels ranged from 0.001 – 0.735 mg/L. Higher concentrations were recorded during the winter turnover phase when bottom and surface waters mixed. Concentration above 0.01 mg/L can cause eutrophication of the water bodies. Total ammonia nitrogen (TAN) ranged from 0.015 - 6.480 mg/L. Higher concentrations were recorded during summer when temperatures were high and depths were low. TAN can be toxic to fish when the pH and temperature are high. The generally low least square means (LSM) for TAN were indicative of minor environmental impact of trout farming operations conducted during the colder, winter rainfall months. Trout farming coincided with conditions where the water temperatures were low, dam levels were high and dams were overflowing. The difference in bottom and surface water quality of reservoirs and the site location were found to be more important than the absence or presence of fish farming. The difference in bottom and surface water is directly linked to the ecological status of the sediment, which serve as nutrient sinks. In monomictic dams found in Mediterranean areas, mixing occurs during the winter turnover phase. Nutrients are released due to surface and bottom water mixing, brought about by torrential rains and wind turbulence. The concentration of organic material in the sediment and bottom waters is a function of the nutrient loading over time, irrespective whether the non-point sources were fish farming or agricultural activities and therefore it is difficult to partition causes and effects. In cases where reservoirs were already eutrophic due to past agricultural practices, implementing aquaculture could exacerbate the poor water quality status of the reservoir. There was a statistically significant difference between fish farming and non-fish farming for phosphorous, Secchi disc, total suspended solids and nitrite-nitrogen (p<0.05) and no statistically significant difference between fish farming and non-fish farming for dissolved oxygen, total ammonia nitrogen and nitrate-nitrogen (p>0.05). There was a statistically significant difference between surface and bottom waters for P and TAN (p<0.05). One reason for higher P and TAN concentrations in bottom waters is the accumulation of both in the sediment and subsequent release in the water column when the water mixes. A two-dimensional scatter plot was generated using the score for the first two principal components. The first two principal components accounts for 40 and 17 % of the total variance respectively, and the two groups of fish farming and non-fish farming did not separate well based on the first two principal components. The occurrence and distribution of phytoplankton biomass fluctuated with dam water levels and nutrient concentrations. The prevailing phytoplankton communities are important to fish farmers for two reasons: 1. It leads to fluctuations in dissolved oxygen concentrations via users (respiration and decomposition) and producers (photosynthesis). 2. It could lead to algal taint of fish flesh when geosmin-producing phytoplankton species are present. The frequency of occurrence indicated that the Group Chlorophyta (including genera, Chlamydomonas, Closterium, Oocystis, Scenedesmus, Staurastrum, Tetraedron, etc) had the most occurrences (n=371) with Chrysophyta (including genera, Dinobryon, Mallomonas, Synura, etc) the least (n=34). There was a statistically significant difference between genera occurrence and season (p<0.05). The geographical location of sites had no significance influence on the frequency of phytoplankton occurrence. There was no direct link between water quality and production yield (p>0.05). The fish yield of farms were linked mainly to the quality of fingerlings and the feed conversion ratio (FCR) achieved (p<0.05). Land-use patterns in the catchment where fish farming dams were located have shown that the dams are multiple-used systems. The ecological integrity of the farm dam ecosystem is dependent on the base volume. The dam is primarily for irrigation and fish farming can be compromised when higher demand for water is required during the dry season. The dams receive about 20 % of its water from rainfall and the rest from runoffs. Farmers could not provide accurate extraction rates making it difficult to predict water levels for future fish production. Four potential mitigation measures to reduce nutrient loading were described namely, feed management (quantity, frequency, type, etc.), feeding method (demand feeders, hand feeding), feed ingredients (formulation) and floating gardens. Both feed management procedures and demand feeders were evaluated as to the efficiency of reducing feed wastage and optimising FCR’s. The small-scale fish farmers were producing approximately 6 tons and had an average FCR of 1.96:1 ± 1.15. If farmers could improve their FCR’s by 0.1 (i.e. from 1.96 to 1.86), it would translate into a reduction of 100 kg feed for every ton of fish produced and result in 5% decrease in nutrient loading. The results of the water analysis and visual assessment of faecal length and colour showed no statistically significant difference between treatments for the guar-gum based binder (p>0.05). In addition, the level of binder did not influence digestibility of the experimental diets. The floating garden study indicated that it was feasible to construct a low cost raft system that is easy to manage and can produce plant crops as a hydroponic system in conjunction with fish farming cages. The lettuces grown on farm dam water provided support for the premise that the water quality can be improved via extraction of nutrients for crop production. For the production of 3.5 kg/m2 lettuce, a ratio of 1.09 plants/fish equal to 1.84 g feed/day/plant would reduce the accumulation of soluble nutrients around floating net cage farming system. The socio-economic evaluation of the contribution of fish farming to the welfare of rural and peri-urban farming communities supported the notion that aquaculture can lead to the upliftment of participating communities. Seventy-one percent (71%) of the respondents indicated that their motivation for exploring aquaculture is to supply fish to the wholesale market in order to generate income. Sixty-one percent (61%) of the respondents conducted the sales themselves or co-opted family members to assist them. The contribution of aquaculture provided direct benefits through improvement in household income, subsistence food supply and skills development. Indirect benefits included providing an information hub for other emerging farmers, elevation of the fish farmer’s status in the community through greater wealth and knowledge creation and promoting sector diversification through new products and technology. The three main constraints to the promotion and growth of aquaculture were listed as lack of government support, insufficient market intelligence and access, and limited choice in the availability of suitable candidate aquaculture species. Irrigation reservoirs in the WCP have a history of enrichment through external sources supplying water via agricultural runoff (fertilisers and pesticides), catchment runoff (leaf litter and organic debris) and stormwater effluent (grey and black water). The incorporation of aquaculture into such dams adds extra nutrients to the water column and management is crucial to limit the nutrient loading and ensure environmental sustainability. Such an approach will ensure that commercial land-based crop farmers’ irrigation regime and water distribution operations would not be negatively affected. Therefore future research needs should focus on; firstly the prevention and minimisation of pollution deriving from aquaculture through improved production management and technology transfer, secondly the monitoring and evaluation of the catchment ecosystem as a continuum with all the external factors affecting the ecology of farm dams and thirdly, evaluating the sediment processes and dynamics as sinks for nutrient accumulation.
Comparison of growth characteristics between the indigenous Oreochromis andersonii and the domesticated Oreochromis niloticus under experimental conditions
(Stellenbosch : Stellenbosch University, 2016-03) Wegener, Anthony Marc; Brink, Danie; O’Neill, Bernadette; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The increase in the world’s population and subsequent growth in demand for fisheries products is coinciding with the over-exploitation and decline of wild fish stocks. Fish however remains an important source of animal protein with more than half of the world’s population depends on fish as a source of animal protein. Aquaculture has become the fastest growing animal production sector with an average increase of 8 percent per annum over the past two decades. The Caprivi region, situated in the North Eastern section of Namibia has the second highest incidence of poverty in Namibia while its wetlands contains diverse habitats and contains approximately 86 resident fish species where habitat preference, breeding strategies, migration patterns and diet can vary inter-specifically. The Caprivi’s fishery plays an important role in that the majority of the population in this region depends on the fishery as a means of income, informal employment and food security. Aquaculture is promoted by the Namibian government as a supplement to the fishery in order to sustain livelihoods of the Caprivi region. Tilapia species has developed into the second most produced freshwater fish in the world, after the common carp (Caprinus carpio), with the domesticated Nile tilapia (Oreochromis niloticus) making up more than 80 percent of tilapia production. The Caprivi region plays host to a wide variety of indigenous tilapia species, including O. andersonii, O. macrochir, O. placidus, T. rendalli, and T. sparrmanii, of which the Three Spotted tilapia (O. andersonii) being the more common and targeted species in terms of the local fishery. Apart from promotion of the undomesticated indigenous O. andersonii for aquaculture purposes, the option remains also to introduce the domesticated and highly successful O. niloticus. Although beneficial in terms of aquaculture potential the introduction of O. niloticus though poses a significant risk of displacing various indigenous tilapia species such as O. andersonii, O.macrochir O.placidus, T.rendalli, and T.sparrmanii as well as affecting the biodiversity of the larger ecosystem. A comparative growth trial confirmed a significantly (P≤0.05) superior growth performance of O. niloticus over O. andersonii in terms of weight and length gain, with the undomesticated O. andersonii also displaying significantly higher variance (CV) for these traits. The growth curve of O.niloticus was isometric compared to the negative allometric growth of O.andersonii. Significant differences (P≤0.05) for moisture and crude lipid content were noted between species, where O.andersonii had higher crude lipid content and O.niloticus had higher moisture content. The proposed approach for developing tilapia aquaculture in the Caprivi region is to establish pilot projects to assess the economic feasibility for the production of the indigenous O.andersonii together with a cost-benefit analysis for the genetic improvement of the species. Furthermore to conduct a risk assessment associated with the introduction of O.niloticus into the Caprivi region with further decisions regarding the appropriate species to be based on the outcomes of the above assessments.
Determination of salinity tolerance limits of tilapia, Oreochromis mossambicus, for use in tuna line fishery
(Stellenbosch : Stellenbosch University, 2003-12) Fitwi, Biniam Samuel; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
ENGLISH ABSTRACT: Many species of tilapia such as Oreochromis mossambicus are euryhaline, able to adapt to different salinity waters. Their ability to withstand high salinity levels has given rise to the possibility of using tilapia as baitfish for tuna line fishery. The purpose of the study was to determine the survival rate of tilapia O. mossambicus during direct transfer from freshwater to the salinity levels of 0, 15, 20, 22.5, 25, 27.5, 30, 32.5, and 35 ppt. The data was analysed through means of univariate ANOVAand regression analysis. O. mossambicus showed no mortality to all salinity regimes up to 25 ppt. Mortality was observed at 27.5 ppt, with 100% mortality at 35 ppt. LC 50 and LC 90 were found to be 30.5 and 34.2 ppt, respectively. The results indicate that tilapia (0. mossambicus) will survive a direct transfer to salinities up to 25 ppt. acclimation will be required in the event of transfer to salinity levels above 25 ppt, in order to prevent significant levels of mortalities.
The effect of dietary L-carntine [i.e. carnitine] supplementation on production performance parameters of Mozambique tilapia, Oreochromis mossambicus, at sub-optimal water temperature
(Stellenbosch : Stellenbosch University, 2004-12) Tekle, Esayas Welday; De Wet, Lourens; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: 60-day growth experiment was conducted to investigate the effect of dietary Lcarnitine supplementation on the production performance parameters of Mozambique tilapia, Oreochromis mosambicus. A number of approximately 140 tilapia fry with average weight of l.4g ± 0.71g were stocked in each of 40 fine-meshed hapas (I mx 1mx 1.5m) submerged within a complete recirculation pond system. During the first 30 days of the experiment water temperatures ranged from 19 to 23°C where after it decreased to 16-20°C for the consecutive 30-day period. Dietary treatments consisted of 8 replicates of 5 levels of L-carnitine supplementation labelled as Co, C250,C500, C750 and C 1000represented Omg, 250mg, 500mg, 750mg and 1000mg L-carnitine supplementation per kg feed respectively. Results were analyzed for significant differences using one-way analysis of variance (ANOVA) and Tukey's pairwise comparison test for growth rate, feed intake (FI) and feed conversion efficiency. After completion of the trial 8 fish from each hapa were sacrificed and analyzed for cephalosomatic index (CSI), dress out percentage (viscera, gills and head excluded), viscerosomatic index (VSI) and hepatosomatic index (HSl). Poor production performance results were generally observed as water temperatures were sub-optimal, especially during the second 30-days period. Results from the trial indicate no significant differences (P>0.05) between treatments for weight gain, FCR, FI and VS!. A negative trend was observed for FCR with increasing level of L-carnitine supplementation for both the first 30-day period (1.50±0.07, 1.53±0.08, 1.58±0.09 and 1.61±0.17 for C250,C50Q,C750and C 1000)as well as for the consecutive lower temperature 30-day period (2.22±0.10, 2.25±0.ll, 2.27±0.28 and 2.29±0.2l for C250, C500, C750 and C 10(0)'Although statistically not significant, fish fed the C250showed better performance in dress out percentage weight either than the control or the higher levels. The increasing trend for head weight with increasing level of L-carnitine supplementation were significant (P<0.05) from Co and C250with and above C500.The decreasing trend for liver weight with increasing level of L-carnitine supplementation became significant (P<0.05) with and above C750.The results of the current study showed a trend in the improvement of L-carnitine on the production performance parameters. However, the natural content of L-carnitine in the basal diet impaired with the inclusion levels, thus further research at lower inclusion levels is recommended.
Effect of Pawpaw (Carica papaya) seed meal on the reproductive, endocrine and immune system of Mozambique tilapia (Oreochromis mossambicus)
(Stellenbosch : Stellenbosch University, 2016-03) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Aquaculture, the farming of aquatic animals and plants, has the potential to solve the problems of dwindling catches from artisanal fisheries as a result of overfishing and habitat degradation. Tilapia species is one of the most cultured food fish worldwide, second only to carp. In Sub-Saharan Africa, which is in dire need of food security, tilapia has the potential to be a cheap source of protein, which through its cultivation, can contribute to poverty alleviation among the rural poor communities. Tilapia breeds effortlessly in captivity, with this attribute which is considered as the “Achilles heel” of the species, because it predisposes pond systems to overcrowding and low weight at harvest. Efforts to mitigate this shortcoming include mono-sex culture of all-males using exogenous hormone to reverse the sex of sexually undifferentiated fish. This is premised on the fact that improvement in the growth by mono-sex culture will lead to shortened production times and a more uniform weight at harvest, which will ultimately benefit the producers. However, the use of exogenous hormones in aquaculture has recently raised concerns about the effect on farm workers, consumers and on the environment. Recently research has focused on the use of substances of plants origin which mimic the action of hormones as a potential approach to achieve sex reversal in fish. Pawpaw (Carica papaya) seed meal (PSM) contains phytochemicals that hold great promise as a sex reversal and a reproductive inhibition agent in aquaculture. The objective of this study was to determine the optimum inclusion levels of PSM that will produce the highest percentage of male brood when included in the diet of sexually undifferentiated Mozambique tilapia (Oreochromis mossambicus; OM) fry of approximately one to two weeks old. Furthermore the study investigated the effects of the PSM on the reproductive hormone profile, haematological and serum biochemical parameters, and gonad and liver integrity of pre-vitellogenic OM. At an inclusion level of 10 g/kg of basal diet, PSM was able to skew the sex ratio in favour of males (60% males to 40% females). The proportion of males increased with an increasing dosage of PSM, with the maximum masculinization achieved at an inclusion level of 20 g/kg BD, resulting in 77.8% males produced. When the masculinization success was compared in terms of the duration of the feeding regimes of one and four months, no significant differences were observed in terms of the number of males produced. The inclusion of PSM did not affect the growth and survival rates, neither did it affect the Fulton’s condition factor of the treated fish. It was found that the PSM investigated lowered the level of plasma 17β- estradiol in female fish but had no effect on the level of the same hormone in males. The plasma levels of 11-ketotestosterone was not affected in both genders. The gonad weight and gonado-somatic index of the male fish were not affected by treatment with PSM, while the gonad weight, GSI, fecundity and egg diameter of the treated females were lower than those of the control. Some of the changes induced returned to normal on cessation of treatment suggesting a reversible reproductive inhibition by PSM. Haematological and biochemical profiles of different treatment groups did not differ throughout the course of the investigation. Liver weight and hepato-somatic index of the treated fish were comparable to those of the control. Histological observations showed minor alterations in the architecture of the liver, with degeneration and vacuolization of hepatocytes in less than 10% of the members in the group fed 30 g of PSM /kg of basal diet for 60 days. However this was not noticed among the group fed 30 g of PSM/kg of basal diet for 30 days, suggesting a possible reversibility of the lesion on withdrawal of treatment. The current research has clearly demonstrated the potential of PSM as a fertility inhibitor and sex reversal agent in OM, with potential application in rural fish farming and feed manufacturing industries. The possibility exist that some of the findings can be adapted to be applicable in other tilapia species like O. niloticus or Sarotheridon galilaeus which together with O. mossambicus constitute the most cultured species in Sub-Saharan Africa.
Effect of phytogenic feed additives on gonadal development in Mozambique tilapia
(Stellenbosch : Stellenbosch University, 2013-03) Ampofo-Yeboah, Akwasi; Brink, Danie; Lambrechts, Helet; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: This study investigated the “Effect of Phytogenic Feed Additives on Gonadal Development in Mozambique tilapia (Oreochromis mossambicus). Aquaculture remains the fastest growing animal food-producing sector and it is set to overtake capture fisheries as a source of food fish, and also to outpace population growth. This rapid growth can be attributed to the increasing demand for aquaculture products, and an urgent need for a sustainable food resource and the safe production of food. Globally, fish provides over 3.5 billion people with up to 15 percent of their average per capita intake of animal protein. The introduction of aquaculture to sub-Saharan African (SSA) took place during the 1940s and 1950s, and the main objectives were to improve nutrition in rural areas, allow for the diversification of activities to reduce the risk of crop failures, to generate additional income, and to create employment opportunities. Aquaculture was seen as a viable option for rural development in SSA, and substantial resources were invested to support its development. Poor results were however, recorded in terms of production and sustainability. Tilapia is the most widely cultured of all fish species farmed, and the second most important group of freshwater and brackish water fish after carps. Tilapia has all the necessary traits that makes it an excellent species to culture, but costefficient production is hampered by the animals attaining sexual maturity at a an early age, which then result in precocious breeding in aquaculture systems. The production of single-sex populations (i.e. all male) is a potential means to address the problem of precocious breeding, but the technologies used to establish single-sex populations are not readily available to resource-poor communities that farm with tilapia for food purposes. Phytochemicals, also known as phytoestrogens, are plant-derived compounds that structurally or functionally mimic mammalian estrogens that affect the sexual differentiation of fish. Phytochemicals occur in plants like Pawpaw (Carica papaya) and Moringa (Moringa oleifera). The study thus had a threefold objective. Firstly, the study investigated the potential of Pawpaw seed meal (P) and Moringa seed meal (M), as part of a commercial tilapia diet, to be used as endocrine disrupting compounds (EDC’s) to control the reproduction of sexually mature Mozambique tilapia (20-45g). Secondly, assess the potential of P and M to inhibit the attainment of sexual maturity in immature tilapia (2-8g). Finally, P and M to determine its influence on sexual differentiation of tilapia fry (9-12 days posthatch) to produce all-male populations. The study indicated that both P and M seeds contain bio-active chemicals that are capable of disrupting the gonad function, differentiation and sexual maturation of Mozambique tilapia. Sperm production was affected, evident in the degeneration of the testicular tissue samples. Egg production, ovulation and spawning were all affected, as evident in the difference in colour of the degrading eggs, as well as the absence of spawning. Ovo-testes were observed in cases where diets containing 10.0g P and 10.0g M /kg basal diet were fed. Eggs were observed in the ovaries of sexually immature fish, but spawning did not occur. The study also presents the first report on the isolation of Oleanolic acid in Moringa seeds. The evident of antifertility properties of both Pawpaw and Moringa seeds can be exploited to control or prevent reproduction of Mozambique tilapia in SSA aquaculture systems. This could be of particular importance to aquaculture development in rural areas of Sub-Saharan African countries, given the abundant year round availability of these compounds. Further studies are required to optimise the preparation of the experimental compounds; as well as determining the optimal inclusion level of the phytogenic compounds, as well as how their efficacy to manipulate the reproductive potential and ability of Mozambique tilapia are influenced by environmental factors such as water temperature.
The effects of probiotics on the physiological and biochemical development of the digestive tract of commercially raised dusky kob (Argyrosomus japonicus) larvae
(Stellenbosch : Stellenbosch University, 2015-04) Hunter, Amy; Pieterse, Elsje; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Aquaculture is one of the fastest growing food producing sectors in the world. Over the past few years, aquaculture research has focused on improving rearing protocols and standards for the culture of aquatic organisms. Probiotics are gaining increasing interest as an alternative to antibiotics to improve animal health and welfare. The effects of probiotics on the physiological and biochemical development of the digestive tract of commercially raised Argyrosomus japonicus (dusky kob) larvae were investigated. Two probiotic treatments were compared to a control where the standard rearing protocol was applied. The growth of the larvae and histological development of the digestive tract was studied. The specific enzyme activity of key digestive enzymes was determined. Amylase, trypsin, pepsin, alkaline phosphatase, aminopeptidase N and leucine-alanine peptidase were assayed. The mean growth of the control group of larvae differs from the CSIR and BactoSafe treatment groups (P = <0.001). There were no differences in the histological development between the control and two treatments. The histology did indicate a slight delay in development of the digestive tract when compared to previous studies on dusky kob. No significant differences were observed between the control and treatment groups for any of the enzyme assays. The effect of probiotics on the development of the digestive system of dusky kob larvae could not be definitively described as it was not determined to what extent the probiotics had established in the gut. What the study did conclude was that the enzyme assays need to be refined in order to determine the optimal reaction conditions required for the determination of specific enzyme activity in commercially raised dusky kob.
The evaluation of biological, mechanical and chemical methods to contain South African abalone species (Haliotis midae)
(Stellenbosch : Stellenbosch University, 2014-04) Fourie, Lize; Lambrechts, Helet; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Haliotis midae (HM) is one of five indigenous abalone species occurring along the coast of South Africa, and is the only species commercially cultivated in open flow-through systems. Commercial production of HM contributes the most to income generated from aquaculture species in South Africa. Exports in 2011 totalled 1036 ton, which amounts to an income of ZAR 369 million (40 million USD). Commercial production of HM is characterized by a long interval (i.e. up to five years) to harvest. Genetic modification of HM to improve growth rate in HM can potentially decrease the interval from hatch to harvest, which will contribute to optimising the cost-efficient production of HM. However, a major concern in the production of genetically modified (GM) abalone is their escape from production systems, and the potential impact of the GM animals on the natural stocks in the surrounding environment. The implementation of containment methods to prevent the escape from GM abalone from production systems will assist in the management of the potential ecological risks escaped GM abalone may pose. Currently no containment strategies exist for the South African abalone industry, which limits the use of transgenic biotechnologies to optimise the cost-efficient production of HM. The study therefore investigated the potential of biological methods (triploid induction), mechanical methods (polypropylene filter bags and obstructive materials), and chemical methods (sodium hypochlorite and chlorine dioxide) to contain transgenic HM in open flow-through systems. Histological evaluation of gonad tissue samples of 16 triploid male and 15 triploid female HM indicated that triploid induction was unsuccessful in arresting gonad differentiation, development, and function. A combination of immature and mature gametes was observed on both triploid male and female gonads. The fertilizing potential of biopsied sperm obtained from triploid and induced diploid male HM was assessed in fertilization trials using ova obtained from diploid HM. No larvae were observed from the fertilization treatments of triploid male biopsied sperm, however, abnormal larvae (0.01% fertilization) were observed when induced diploid sperm were used to fertilize diploid ova. Polypropylene filter bags (100 μm) were not effective in containing male and female gametes in the broodstock section of the abalone culture system used in this study, and future studies should address specialized methods of containment of HM gametes. Polypropylene filters (100 μm), resulted in effective containment of larvae and settlement larvae, and in this study was not a more effective method of containment than the current on-farm larvae containment protocol. The three obstructive materials were effective in containing HM spat, and did not differ in their ability as containment methods. Sodium hypochlorite and Biox™, chlorine-based chemicals, were effective in containing the five life stages of HM, i.e. sperm, ova, larvae, settlement larvae and spat. The respective life stages were exposed to varying concentrations of the respective chemicals (i.e. 10 ppm, 50 ppm and 100 ppm) over five exposure times (i.e. 4, 6, 8, 10 and 12 minutes). Sodium hypochlorite and Biox™, at the different concentrations and exposure times, resulted in mortalities in all five HM life stages, with higher incidences recorded at the higher concentrations evaluated. Future research on the effect of triploid induction on the endocrine system, and how effective gonad maturation and function is suppressed, needs to be conducted. The aspects of mosaics occurring in induced diploid animals warrant further investigation with a larger sample size to verify the findings of this study. The production of true sterile individuals would improve the results to use of GM animals as a method of biological containment. Incorporation of mechanical containment methods need to be kept in mind when abalone production systems are designed. The use of chemical containment methods warrants additional studies on the practical administration and the economic feasibility of the chemical into the water supply of open flow-through abalone culture systems.
Evaluation of spirulina on the performance and pigmentation of rainbow trout
(Stellenbosch : Stellenbosch University, 2004-04) Stander, Hendrik Barend; De Wet, L. F.; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: trout was conducted at the Jonkershoek trout research station of the Division of Aquaculture, University of Stellenbosch. Treatments consisted of ten experimental diets containing increasing levels of Spirulina (0%, 0.05%, 0.1%, 0.15%, 0.3%, 0.6%, 1.25%, 2.5%, 5% and 10%). The data was analyzed through means of a one-way ANOVA and Tukey’s pair wise comparison test for significant differences between treatments for the various parameters of flesh pigmentation and growth. The results indicates that the inclusion of Spirulina in the diets of rainbow trout will cause a undesirable yellowing of fillets, particularly at levels of inclusion at 5 percent and above, which may limit its use in diets for rainbow trout. There was an inconsistent increase in b* (yellowblue) and Chroma values with increasing levels of Spirulina inclusion, which may indicate the deposition of carotenoids (yellow-orange colour range) instead of the desired deposition of xanthophylls (pink-red colour range) in the flesh of the rainbow trout. This increase in b* (yellow-blue) values was significantly higher (P<0.05) at inclusion levels above 5 percent. Spirulina had no significant effect on weight gain of rainbow trout at any level of inclusion. No significant differences (P>0.05) were observed in any of the other production performance parameters (growth rate, feed intake, feed conversion ratio, viscerosomatic index, hepatosomatic index, and liver lipid content) that were evaluated. Low mortality rates were observed with no significant differences between treatments. A trend of decreased feed intake with increased levels of Spirulina inclusion became significant at the 2.5 percent level of inclusion, caused by deterioration in the palatability of the feed. A significantly higher dress-out percentage was observed at levels of Spirulina inclusion above 5 percent. A trend of decreased liver lipid content with increased Spirulina inclusion was observed, though not significant at any level of Spirulina inclusion. This observation justifies further investigation because of its potential to improved carbohydrate metabolism in carnivorous fish Results confirm that up to 10% Spirulina can effectively replaced soybean meal in the control diets for rainbow trout while simultaneously improving carcass dress-out at high inclusion levels.
Genetics studies of cichlid Oreochromis shiranus towards sustainable aquaculture and fisheries management in Malawi
(2020-12) Sanudi, Thomson Joseph; Roodt-Wilding, Rouvay; Rhode, Clint; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
ENGLISH ABSTRACT: Oreochromis shiranus is an economically important fish species in Malawi, but levels of harvest from the wild have declined due to overexploitation and habitat degradation. There is an urgent need to devise strategies for sustainable utilization of this species. The aim of this study was to understand the reproductive behaviour, geographic distribution, genetic diversity, population structure, past demographic fluctuations and association of quantitative trait loci (QTL) with traits of economic importance which are prerequisites for the design and implementation of these strategies. A random sample of 306 live fish, collected across the main water bodies in Malawi, were reared in one pond to reproduce an F1 generation in random families. This study observed that mate selection and competition among the females for males and mating sites resulted in only a few females (42%) and males (27%) contributing to the F1 generation. However, there was no statistically significant variation in genetic diversity between the broodstock and the F1 generation, because of the large genetic base and participation of broodstock from all the sampled locations. The study concluded that due to limited gene flow, O. shiranus populations in the wild in Malawi were structured according to and within water basins. There was evidence of population bottlenecks in the wild, which corresponded to small effective population sizes (Ne = 104). The population bottlenecks did not result in low genetic diversity and inbreeding depression due to isolate breaking. Finally, the association of some QTLs for body weight in Oreochromis spp. suggest considerable evolutionary conservation and synteny within the genus. The observed levels of genetic diversity and Ne across the main water bodies in Malawi are adequate to increase Ne and mitigate against future bottlenecks if closed fishing seasons and fishing net mesh size are enforced. Restocking programmes may not be necessary at the moment unless in the event of complete desiccation. During restocking, it is therefore recommended that, to ensure genetic diversity, broodstock for stock enhancement should be randomly sampled from the different populations within the water body. In aquaculture, where interest is to increase production of large fish, these findings will greatly inform management and breeding programmes to ensure genetic diversity and increase selection efficiency by using QTLs. Although it was not possible to determine the ideal number of individuals that should be included as founder population for selective breeding programmes, this study recommends that a wide genetic base is required to ensure genetic diversity. The results of this study are useful in conservation management of the species in the wild and the establishment of genetic improvement programs in aquaculture.
A growth comparison among three commercial Tilapia species in a biofloc technology system in South Africa
(Stellenbosch : Stellenbosch University, 2015-12) Day, Scott Bowerbank; Salie, Khalid; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: With environmental conservation playing a growing role in decision making today, the aquaculture industry has sought new innovative ways to reduce the impact on the environment, and maximize efficiency. Much of the focus of such developments has included lower water usage and better feed utilization, with the emergence of biofloc technology systems addressing such needs. Tilapia has been identified as a fish for the future, with its production having already risen to make it an important food fish globally, and an increase in its market share is predicted going forward. Although it is common around the world, the production of tilapia has failed to take off in South Africa, with the reasoning being put forward including; legislative restrictions, unfavourable climate, incorrect species choice and shortage of expertise and supporting industry. The major aims of this study were to address the main constraints and uncertainties facing the local tilapia industry in terms of species choice, and to investigate the biofloc technology concept under local conditions. Being restricted to the use of the Mozambique tilapia (Oreochromis mossambicus), and with the recent changes allowing the use of the Nile tilapia (Oreochromis niloticus), the question whether O. niloticus will in fact outperform O. mossambicus under South African conditions, was raised. With the production of the Three Spot tilapia (Oreochromis andersonii) also prevalent in southern Africa, this species was also included in the study. The secondary aim of the study was to create a profile of key water quality parameters during the start-up period of the biofloc technology system prior to fish being introduced, and throughout the course of the trial. With the biofloc technology concept being expected to play a role in the development of the South African tilapia industry, the study was conducted in a biofloc technology system. Twelve tanks, connected through airlift pumps to homogenize the water quality, were stocked with fish. Each of the three species were stocked randomly into four tanks with each tank being considered an independent replicate. The growth trial was conducted within a greenhouse, and commenced at the start of the summer grow out period for tilapia in South Africa, in October 2014, running for 10 weeks. Fish were sampled fortnightly from the system, with the mass data being used to fit a linear regression. Water quality measurements were taken from the start-up period in mid-September, for 12 weeks. Profiles for temperature, dissolved oxygen, pH, salinity, electro-conductivity, total dissolved solids, floc volume, total ammonia nitrogen, nitrite, nitrate, orthophosphate, total suspended solids and turbidity were successfully documented over the trial period. Two spikes in total ammonia nitrogen and nitrite were recorded, one during start-up, and one following a water loss event during the trial. A regression fitted to the mass data showed O. niloticus to have the highest growth rate with an average daily gain of 0.693±0.018 g/day, followed by O. mossambicus of 0.405±0.025 g/day, and then O. andersonii of 0.185±0.025 g/day, with significant difference between all three species. The lowest feed conversion ratio was also recorded for O. niloticus being 1.00±0.05, followed by O. mossambicus of 2.24±0.16, and O. andersonii with 2.53±0.28. These results suggest that of the three species investigated, O. niloticus performs best in a biofloc technology system in South African conditions. It is recommended that this species should therefore be used in biofloc technology systems as they develop in South Africa.
Gustatory and olfactory feeding responces in Japanese koi carp (Cyprinus carpio)
(Stellenbosch : University of Stellenbosch, 2006-03) Barnard, Philip; De Wet, L. F.; Brink, Danie; University of Stellenbosch. Faculty of Agrisciences. Dept. of Animal Sciences. Aquaculture.
Chemo-attraction and –stimulation facilitate the initial location (olfactory response) and final consumption (gustatory response) of food in the feeding process of fish. Chemo-attractants or chemo-stimulants is therefore generally included in feeds for especially slow-feeding species to help reduce water fouling and to promote feed efficiency and growth rate through improved feed intake. Considering this, a study was performed to evaluate the attraction and stimulation potential of selected cereals and free amino acids in diets for Japanese koi carp (Cyprinus carpio). Results are presented on the comparative evaluation of five cereals (maize, sorghum, wheat, rye and triticale), raw and cooked forms of maize and concentrations of betaine and selected free amino acids (alanine, arginine, lysine and methionine), as well as their additive effect.
An investigation of the survival level of Oreochromis mossambicus fry variably kept in a closed system : laboratory experiment
(Stellenbosch : University of Stellenbosch, 2005-04) Asgodom, Mihretu T.; De Wet, Lourens; Brink, Danie; University of Stellenbosch. Faculty of Agrisciences. Dept. of Animal Sciences. Aquaculture.
This paper contains literature on tilapia culture, feeding and nutritional factors of prime consideration to survival and growth of Oreochromis mossambicus. Results are presented for a three-phase laboratory experiment on survival of O. mossambicus fry in an attempt to evaluate the use of live Spirulina platensis. The experiment was conducted on fry in a closed system in an effort to maximize the use of live Spirulina and also optimize growth and production. Fry were tested for tolerance levels of salinities, 0-35 g/lt, and showed favourable survival rates up to 15 g /lt salinity without being fed. Manipulation of input in freshwater turned high fry mortalities with increasing rates without difference for physical form of Spirulina. Growth was not significantly affected by types of input. However fry grew well at 0-40% rates with considerable survival performance. It is noted good quality of water that allow improved survival and growth of fry in a closed system may be assured with rates of input up to 5 or 10% of bodyweight. These input rates can guide use of live Spirulina in saline water tilapia culture if Spirulina proves good productivity at the consistency of fry tolerance to the salinity levels established in this paper.
Mitigation methods for Terebrasabella heterouncinata, a problematic sabellid polychaete, populations within an abalone (Haliotis midae) production system
(Stellenbosch : University of Stellenbosch, 2006-03) Henderson, Ray Arthur; Brink, Danie; Britz, Peter; University of Stellenbosch. Faculty of Agrisciences. Dept. of Animal Sciences. Aquaculture.
T. heterouncinata is a sabellid polychaete endemic to South Africa and found primarily in the shells of the abalone Haliotis midae. With the intensification of abalone aquaculture around the world, T. heterouncinata has become a problematic pest by causing shell deformities, reducing abalone growth rates and, in some instances, high abalone mortalities. The problem of this sabellid was first noticed in Californian in the early 1980’s in Red abalone (Haliotis rufescens) production facilities. Many mitigation methods have been tested over the years and this paper investigates another two methods; a reduction in particulate load in the tank to reduce the food source of the sabellid which perhaps will reduce fecundity, and to use ultrasound as a possible mitigation method. This study found that filtration and reduction in suspended particles did not have a significant effect, but that ultrasound did have a significant effect in reducing T. heterouncinata populations.
Polydorid polychaeta as pests in cultivated oysters : a case study of polydorid infestation on a South African oyster farm, including a literature review and proposed best management practices for the reduction of polychaete infestation in the culture of molluscs
(Stellenbosch : Stellenbosch University, 2006-04) Brink, Jacobus Abraham; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Reports of a wonnlike "parasitic" infestation of pacific oysters, Crassostrea gi.gas combined with an increased mortality on a land based oyster farm on the west coast of South Africa prompted an investigation as to the identity of the infesting organisms, the extent of the infestation and the impact on the condition of the oysters. As the infesting organism was suspected to be a member of the polydorid complex of the spionid polychaeta, a literature study was conducted and the information gathered, compiled in the form of a review which also serves the purpose of a practical guide for aquaculturists who have to deal with polydorid infestations. The review summarizes information on the systematics, life history, impact and control of the group. The infesting organism was identified as a member of the spionid polychaeta and specifically the genus Polydora, a known pest in bivalve molluscs. It was found that the organism showed varied levels of infestation in the spatially and age segregated oyster population on the farm with the oldest animals the heaviest infected and also the possible source of the infestation as they were brought onto the farm from another oyster farm. The condition of all the animals in the different cohorts on the farm was good compared to international standards (condition indexes (Cl)> 10) ANOV A analysis of data could find no significant difference between the condition of infested and uninfested oysters and therefore it cannot be conclusively proved that the increased mortalities can be ascribed to the polydorid infestation. Although no single cause seemed to be implicated the mortalitie can probably ascribed to a combination of several extrinsic and intrinsic factors. The implementation of quality control systems such as HACCP on aquaculture farms is critical for successful cultivation. A set of Best Management Practices (bmp) for the culture of bivalve molluscs is proposed, with identification and special reference to the critical control points as required by HACCP. The current practices on the farm in question were also investigated and it was concluded that the absolute lack of management on the farm was the primary cause for the · problems experienced.
A production model for commercial integrated aquaculture development in KwaZulu-Natal using family scale modular units
(Stellenbosch : Stellenbosch University, 2005-03) Joubert, Gerard Michel; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: This paper reviews the status of world aquaculture with a primary focus on Sub-Saharan and Chinese freshwater aquaculture, and proposes a commercial integrated farming model for implementation in rural areas in KwaZulu-Natal. The model combines the paradigms of age-old Chinese integrated pond farming principles with a commercial approach in the socio-economic context of Sub-Saharan Africa. The project's objective is to contribute to the alleviation of poverty through economic development in rural areas using environmentally and economically sustainable farming practices. The project's medium-term goal is to achieve the critical production volume to warrant vertical integration into a hatchery, feed mill and processing facility. Integration would reduce operating costs and afford better standards of basic services. The project's long-term goal is to grow and expand the model to make a contribution to global food security through distributing a fish-based, nutritionally balanced meal to famine relieve efforts in low-income food deficiency countries (LIFDC). The model proposes the development of individual farms each with a production capacity of 40 to 60 tons of fish per annum. The species available include tilapia, catfish, carp, mullet, bass and eels. The farms will each consist of eight grow-out fishponds totalling 4 hectares of water surface area, a basic homestead and 6 hectares for crops and livestock rearing. The farms are designed to utilize the nutrient rich effluent from the fishponds to flood-irrigate crops planted in the fields below. Through application of the principles of the integrated approach to fish-crops-livestock farming as applied by the Chinese over the last 2,000 years, the farms are designed in a way that nothing is wasted. The waste product from one system becomes input for the next system. The integrated approach is extremely cost effective and lends itself to total organic farming adhering to environmentally responsible and sustainable farming principles. Two hundred such farming units would produce a total of 8,000 to 12,000 ton per year that equates to double the current combined freshwater aquaculture production from all the SADC member countries.
Quantifying the effect of inbreeding on the growth and yield of Mozambique Tilapia (Oreochromis mossambicus) over three generations of repeated full-sib mating
(Stellenbosch : Stellenbosch University, 2015-12) Akinoshun, Kolawole M.; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The effects of acute inbreeding on growth performance, yield and occurrence of deformity traits were studied in experimental full-sibling inbred populations of Mozambique tilapia Oreochromis mossambicus at three levels of inbreeding coefficients, namely F = 0.000, F = 0.250 and F = 0.375. The base population with F = 0.000 was established through the crossing of two geographically separated and genetically unrelated farm stocks. At each generation, the inbreeding depression indicated by body weight (BW), standard length (SL), specific growth rate (SGR) and yield were highly significant, but no linear relationship was found between level of inbreeding and inbreeding depression. Both condition factor (K) and the number of observed deformities appears not to be significantly affected by inbreeding at all three levels. Over all, the average inbreeding depression at F = 0.250 and F = 0.375 respectively was found to be 46.5 percent and 46.6 percent for body weight (BW); 18.2 percent and 18.0 percent for standard length (SL); 21.8 percent and 20.3 percent for specific growth rate (SGR) and 5.752 percent and 8.940 percent for flesh yield. The outbred Control group differed significantly (P<0.05) from the six inbred family groups in terms of body weight (BW), standard length (SL), specific growth rate (SGR) and yield at all levels of inbreeding studied (F = 0.000, F = 0.250 and F = 0.375). Average inbreeding depression for body weight (BW) amongst the six inbred families ranged from 39.6 to 54.2 percent at F = 0.250 (in Gen 2) and 45.6 to 47.3 percent at F = 0.375 (in Gen 3). The inbreeding depression coefficient for body weight (BW) per 10% increase in F, amongst the six inbred families, ranged from 15.9 to 21.7 percent at F = 0.250 and from 12.2 to 12.6 percent at F = 0.375. Average inbreeding depression for standard length (SL) amongst the six inbred families ranged from 14.0 to 22.3 percent at F = 0.250 and from 17.2 to 18.4 percent at F = 0.375. The inbreeding depression coefficient for standard length (SL) amongst the six inbred families ranged from 5.6 to 8.9 percent at F = 0.250 and from 4.6 to 4.9 percent at F = 0.375. Average inbreeding depression for specific growth rate (SGR) amongst the six inbred families ranged from 17.9 to 27.9 percent at F = 0.250 and from 16.7 to 27.2 percent at F = 0.375. The inbreeding depression coefficient amongst the six inbred families ranged from 7.2 to 11.2 percent at F = 0.250 and from 4.5 to 7.3 percent at F = 0.375. Average inbreeding depression for yield amongst the six inbred families ranged from 0.4 to 7.7 percent at F = 0.250 and from 8.5 to 10.2 percent at F = 0.375. The inbreeding depression coefficient for yield amongst the six inbred families ranged between 0.2 and 3.1 percent at F = 0.250 and from 2.3 to 2.7 percent at F = 0.375. The condition factor (K) of the six inbred families showed no significant differences to the Control (P > 0.05) at all levels of inbreeding with K-values ranging from 1.42 to 2.85. The occurrence of morphological deformities in all seven family groups including the Control showed no noticeable trend, with a random, nonlinear occurrence of fluctuating asymmetry observed at different inbreeding levels in O. mossambicus. This study demonstrates that inbreeding has a significant negative effect on the production traits of Oreochromis mossambicus, especially growth. Results from this study emphasize the need to create awareness amongst small scale farmers of the importance of preventing uncontrolled inbreeding in production systems, as well as to monitor inbreeding levels during the process of dissemination of improved fish strains to small scale fish growers in developing countries, including Africa.

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