Effect of cage fish culture on the diversity and abundance of zooplankton in Tende bay Lake Victoria

Abstract

Aquaculture is one of the fastest growing sectors in Uganda, producing up to 15000 tonnes of fish from small-scale farmers, emerging commercial fish farmers and stocked community water reservoirs and minor lakes. In order to cater for the increase in demand for animal protein, manifold fish rearing methods have been created and employed, one of which is cage fish farming. A fish cage is a meshed enclosure which is placed into a body of water to confine the fish in captivity until they grow to the required size. Fish cages can be put in freshwaters for fresh fish, or in marine waters for saltwater fish. Majority of Lake Victoria’s Bays are subjected to aquaculture production, one of which is Tende Bay. Two fish farms are situated in Tende bay, that is Pearl aquatics fish farm and Victoria treasures. However much the production of fish has solved the problem of low fish catch from the wild, the fish in cages impacts the water of Lake Victoria negatively. There is deposition of materials from fish cages directly into the water, which distorts the physical parameters and chemical parameters of the water. It also brings about change in the aquatic biota thereby altering the ecology of the lake and subsequent loss of biodiversity. The research is based on studying the community of zooplankton and the physico-chemical parameters of water, in order to find out the extent of cage culture practices on the water environment of Tende bay. Water samples for zooplankton were collected from selected three sites on Lake Victoria, that is site A, site B & site C. The water parameters were measured in-situ and analyzed using one-way ANOVA and Mann- Whitney U test to test the differences. Zooplankton species abundance and diversity were done using Kruskall-Wallis test and Shannon-Wiener Diversity Index respectively. The results of the three study sites compared, indicated minimal variation in the physico- chemical parameters (p<0.05), while oxygen indicated no significant difference (p=0.1598). The results for zooplankton species abundance indicated no significant differences between the study sites. The fish cages thus had observed low impact on the lake water of Tende bay.