Fish community structure of Weija Reservoir after 28 years of impoundment

Abstract

The fish community structure of Weija Reservoir after twenty eight (28) years of impoundment was investigated to formulate management strategies and interventions for sustainable fisheries development. Monthly fish sam-pling was undertaken with gill nets of various mesh sizes from March to December 2005. Sixteen species repre-senting 11 genera and 7 families were recorded, indicating declining fish species richness due to disappearance of marine species and restructuring of the fish community in response to change from riverine to lacustrine con-ditions. Cichlid, mainly, Tilapia guineensis and Hemichromis fasciatus and Cyprinids, mainly B. macrops supp-orted about 69.6 % of total weight (mass) and 93.8 % of total number. About 37.14 % of all fish species ever recorded from the reservoir have disappeared and about 6 % have appeared, indicating that the fish community is undergoing restructuring. Semi-pelagic omnivores and aufwuchs-detritus herbivores constituted the most im-portant trophic groups accounting for about 65 % of both total weight and number. The Forage/Carnivores (F/C) ratio of 4.97 and 2.43 in terms of weight and numbers indicated acceptable ecological balance among the fish population. For effective fisheries development, regular biological monitoring of the major fish species, contr-ol of unapproved fishing practices and anthropogenic activities that accelerate habitat destruction and environm-ental degradation must be instituted.