Environmental quality and fish communities in selected catchments of Lake Victoria

Abstract

Water quality and fish species are studied in selected catchments of Lake Victoria. The major aim of the study is to establish the relationship between the environmental quality and fish communities in the selected study sites of Lake Victoria. Physico-chemical characteristics of water in selected sites were determined on-site while nutrients and heavy metals were determined in the laboratory using standard methods. Fish samples were collected using experimental multifilament gillnets with varying mesh sizes. Fish identification was done using external morphological characteristics and identification keys. Physico-chemical results in Thruston bay revealed rise in water column temperature and turbidity as compared to those measured by earlier studies on the lake. Dissolved oxygen (DO) ranged from 0.9 mg L-1 in Yala catchment to 11.56 mg L-1 in Thruston bay. Phosphorus (P) ranged from 9.78 g L-1 to 120.67 g L-1 in Thruston bay and in Yala catchment, it ranged from 185.2 g L-1 to 1526.9 g L-1. The nitrate-nitrogen loading in the Geita catchment ranged from 130 to 7465 kg N between the years 2006 and 2008. The results in the inshore sites show a potential for higher photosynthetic rates than in the offshore sites implying that there is more food for the fish in the inshore sites than in the offshore sites. Results further reveal that in Thruston bay there are 13 fish species and Haplochromines dominate the fish catch in terms of numbers. Heavy metals including mercury resulting from artisanal and commercial gold mining in the Geita study site were also detected in the discharges into the lake. This paper also presents measures for the sustainable management of the lake environment, its quality and fisheries.