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

Abstract

The endemic Oreochromis variabilis and L. victorianus are among Lake Victoria’s most threatened fish species whose population sizes are on the decline. This study, carried out between August 2000 and April 2001, aimed at characterizing the ‘refugia’ ecosystems of O. variabilis and its growth performance in small water bodies (SWBs), developing artificial spawning techniques and characterizing existing morphological and genetic variation of extant populations of L. victorianus in order to bring the species under aquaculture 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 eco-zones, 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 eco-zone. 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 their stocking programs; yet ensure that different age classes form part of their brood-stock. 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. Fertilization 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. More hope is therefore raised 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 further, the integrated resource use and management of the endemic but threatened Lake Victoria fish stocks.