The potential of mukene (Rastrineobola argentea) fishery in Lake Victoria with suggestions for its management

Abstract

Following the decline in catches of endemic fish species in Lake Victoria, Mukene, Rastrineobola argentea has become an important commercial fish species. The fishery spread first through Kenyan, and Tanzanian waters and is now well established in the Ugandan portion of the lake. Rastrineobola, together with the Nile perch and the Nile tilapia are the three most important commercially exploited fish species in Lake Victoria now. High mortality due to human exploitation and predation pressure by the Nile perch have contributed to changes in biological characteristics of mukene populations. Monthly samples of mukene covering at least a calendar year were obtained from the artisanal fishermen operating in Lake Victoria. These were analyzed for size structure, growth, gonad maturity state and breeding periodicity. Type and quantities of by-catch species and parasite infestation were also determined. Size structure of mukene populations has reduced from a mean of more than 60 mm SL in the early 1970’s to 44 mm SL in 1997. A five or three mm-mesh net, which captures may immature fishes, has replaced a 1 mm mesh net. Catches from closed bays and near shore areas contain a high proportion of juvenile mukene, tilapia and Nile perch as by-catch. In the “islands” belt of Lake Victoria, where the bulk of mukene fishing occurs, high proportions of immature mukene is caught during the months of November/December. This is the time when young mukene are recruited into the fishery and should be closed to fishing. Considering the above changes to mukene populations in the lake, a 10-mm mesh net previously recommended for harvesting the species, may no longer be suitable. R. argentea should therefore be exploited away from the shore line and closed bays using nets with minimum mess size of 5 mm.