CHARO, H. 1, J. MAITHYA1, J.B. OKEYO-OWUOR2, B.C.C. WANGILA3, M. HOGGREN4, J. DANNEWITZ5 & M. CARLSSON5

1KMFRI Sangoro Aquaculture Research Station, P.O. Box 136, Pap-Onditi, Kenya
2School of Environmental Studies, Moi University, P.O Box 3900, Eldoret, Kenya
3Fisheries Department, Moi University, P.O Box 3900, Eldoret, Kenya
4Evolutionary Biology Center, Norbyvagen 18D, 75236 Uppsala, Sweden
5Swedish Biodiversity Centre, Box 7007, SE 750 07 Uppsala, Sweden

Aquaculture strategy for restoration of threatened Lake Victoria fish: The case for Oreochromis variabilis (Boulenger, 1906) and Labeo victorianus (Boulenger, 1901)

The endemic Oreochromis variabilis and L. victorianus are among Lake Victoria's most threatened fish species. The population numbers are on the decline. This study is aim at characterising the refugia ecosystems of O. variabilis and its growth performance in small water bodies (SWBs), developing artificial spawning techniques and characterising existing morphological and genetic variation of L. victorianus populations as a restoration strategy. Studies of O. variabilis were carried out by comparing its growth performance in stocked semi-intensive and modified extensive closed systems in different ecological zones within the Lake Victoria basin. Growth in O. variabilis, evaluated as average growth rates, was satisfactory in both systems and ecozones, even in areas with extreme environmental gradients. The isometric characteristics of O.variabilis estimated by formula W = aLb were better than those of wild populations in the refugia ecosystems in each respective ecozones. Multivariate analysis of morphological data showed that there was reasonable differentiation between L. victorianus populations from different drainages, with the southern populations being most distinct. Majority of the variation in L. victorianus was within populations (91.3%), with an overall FST of 0.08846 for all loci. For effective aquaculture and conservation, fish breeders should use local fish material for stocking programs and ensure that different age classes form part of their broodstock. L. victorianus was spawned artificially using intramuscular injection of Clarias gariepinus pituitary extracts (C.g.PE) and Human Chorionic Gonadotropin (HcG) to induce ovulation. Successful inducement of ovulation occurred only in trials with C.gPE. Fertilisation rates in breeding experiments for L. victorianus averaged 86% and hatching percentages 70%. This study indicates the viability of the two species for culture in the basin. There is optimism for expansion on the farming practices in the basin. Such a fisheries production can provide 75% of the animal protein requirements of the poor rural households and guarantee continued survival of the species within the basin. Stocking of small water bodies for increased fish production enhances the integrated resource use and management of the endemic but threatened Lake Victoria fish stocks.