Whole body and egg amino acid composition of Nile perch, Lates niloticus (Linnaeus, 1758) and prediction of its dietary essential amino acid requirements

Eggs and tissue of Nile perch juveniles were analysed in order to derive the essential amino acid dietary requirements for Nile perch larvae and juveniles, using the A/E ratio. Results revealed the presence of both essential and non-essential amino acids in Nile perch. A significant difference (p < 0.05) between the amino acids (AA) composition in the eggs and tissue and amongst the four class sizes of juveniles was observed. Estimates of the amino acid dietary requirements revealed that Nile perch has high arginine, leucine, threonine, valine and isoleucine dietary requirements.Key words: Nile perch, amino acids, dietary requirements, larvae, juveniles

Reproductive biology of ningu, Labeo victorianus (pisces: cyprinidae), in the kagera and Sio rivers, Uganda

We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability

Induced ovulation, spawning, egg incubation, and hatching of the cyprinid fish Labeo victorianus in captivity

Ningu Lubeo victorianus is the only labeine fish within Lake Victoria and its catchment (Greenwood 1966; Reid 1985). This species, once widely distributed in the Lake Victoria basin and supporting a commercial fishery until the late 195Os, has declined due to overfishing (Cadwalladr 1965; Ogutu-Ohwayo 1990; Seehausen 1996). The L. victorianus fishery has not only collapsed but the species has also disappeared from some of its former habitats. Recent surveys in Uganda have only found two distant populations-one in the Sio River on the Uganda-Kenya border (0” I3’53”N, 34”00’30’E), and the second in the Kagera River on the Uganda-Tanzania border (0°56’28.1”S, 3 1’46’ 18”E) (Rutaisire 2003) (Fig. 1). Currently, there is growing interest to breed the fish for wild stock enhancement and culture as a food fish

An overview of domestication potential of Barbus altianalis (Boulenger, 1900) in Uganda

Domestication of fish is a key strategy for diversification of farmed species to meet consumer’s choices and demands as well as conservation of the species for sustainable provision of nutrition benefits and incomes. Initial successful induced spawning of Barbus altianalis was achieved, but there is low adoption attributed to lack of sufficient quality seed. This paper reviews the ecological and social-economic trends, and potential prospects that justify the domestication of this high value indigenous species, and identify gaps that could be addressed to increase seed production for commercialization. Review findings show that due to overexploitation, there is a steady decline of B. altianalis in Ugandan water bodies, with no current record from Lake Victoria where catches had in the past been reported. B. altianalis shows ability to survive in interlacustrine-riverine environments although, the juveniles are largely confined in the river or stream water. Varying levels of adaptability and tolerance to environmental conditions including oxygen and temperature by different age groups occur. The species has a great potential for culture as an omnivorous species with high chances of adapting to varying feeding strategies. Knowledge gaps in size at maturity, appropriate inducing hormones, growth conditions, egg hatchability and larvae weaning were identified as key challenges associated with B. altianalis domestication. Understanding the underlying natural ecological dynamics of B. altianalis will guide further research in the areas mentioned to ensure advancement in domestication so as to meet the rising demand for B. altianalis. This will curtail its overexploitation in the wild and also improve the livelihoods of the communities in the region. Keywords: Cyprinid, Omnivorous, Indigenous species, Domestication, Commercializatio

Aquaculture for increased fish production in East Africa

Fish is produced for human consumption and other purposes through capture fisheries and aquaculture. Fish production from natural stocks has already reached its limits and is declining while aquaculture production is increasing. Aquaculture is making a significant contribution to fish production in several countries thus proving to be a potential alternative to supplement the declining capture fisheries. In East Africa the contribution of aquaculture to the total fish production is still insignificant although it has been practised in the region since the 1900s. The predominant aquaculture production system in East Africa at present is small scale earthen ponds characterised by low inputs and low yields. Important ingredients for the emergence of a commercial aquaculture industry are highlighted with emphasis on the need for a conducive and harmonised policy framework across the region. This paper advocates a focused plan of action for aquaculture development in the region and makes succinct recommendations for fast transformation of the industry.Key words: Aquaculture, East Africa, Lake Victoria basin, production, marketing, regulation, new technologie

Morphology and functional ontogeny of the digestive tract of Barbus altianalis larvae

The ontogenetic development of digestive structures in Ripon barbel (Barbus altianalis) larvae was investigated using standard histological and histochemical procedures from hatching up to 60 days after hatching (DAH). The study was conducted to determine the best period of exogenous feeding and the stage when the digestive tract is able to digest processed microdiets. Results indicated that at hatching, the digestive tract, mouth and anus were closed. The opening of the mouth and anus were observed 3–4 DAH, whereas complete separation of the entire gut was observed on 5 DAH. Exogenous feeding started 5–6 DAH, but complete yolk exhaustion occurred 7–8 DAH, indicating a period of mixed feeding. Mucosal epithelial folds were first noted 3 DAH in the anterior intestine and became profound with some goblet cells (mucous cells) by 6 DAH. At 7 DAH the mucous cells had started secreting both neutral and acid glycoconjugates. The first intestinal single loop occurred at 28–30 DAH and a double loop at 45–50 DAH. Each coiling was proceeded by larval weight increase. By 7 DAH the buccopharyngeal cavity was lined by a layer of squamous epithelial cells with scattered goblet cells and tastebuds that became numerous by 15 DAH. At hatching, the liver and the pancreas were undifferentiated, but on 3 DAH the hepatocytes and zymogen granules of the pancreas became clear. By 7 DAH both organs enlarged, making extensions into the posterior. Intestines coiling at 28–30 DAH coincided with the beginning of external dressing of the scales, a period when B. altianalis started transforming into a juvenile. By 7–8 DAH the digestive structure showed all the necessary digestive features that could enable the larvae to digest any compound diet suggesting that it may be feasible to substitute or offer a complete microdiet during larvae nursing with reduced larval mortality.Keywords: digestive structures, exogenous feeding, microdiet, mucins, ontogenetic development, Ripon barbe