Abstract

Akinlade S. Temenu

The natural diversity of most aquatic systems has witnessed various changes in stock diversity and abundance resulting from structural changes in habitat, food composition and uncontrolled exploitation. These have altered the ecology of the fish resources with the disappearance of some species and dominance of others. This study seeks to identify the ecological implication of the stock diversity and abundance in Lake Asejire. Lake Asejire is a 525 ha man-made lake on river Osun one of the major rivers that drain the western part of Nigeria. Fish samples were collected for a period of 24 months using gillnets of between 25 and 187.5 mm mesh sizes. Data obtained were analyzed using inferential statistics and descriptive analysis of means, frequencies and percentages. Seventeen families identified and grouped into trophic levels. Herbivores were 63.03 and 60.35%; carnivore 31.05 and 30.65% and omnivores were 5.91 and 8.99% by biomass in the first and second year respectively. The herbivores were dominated by the cichlids, heterotis and cyprinids; carnivores by bagrids, characids, channids and Lates while mormyrids, synodonts and clarids constitute the omnivores. Seasons had no effect on the population and number of the carnivores. The carnivore to herbivore ratio (F/C) was 1.33 and 0.9 by number and 1.7 and 1.33 by biomass; this is of concern as this could pose a threat to ecological balance. It is recommended among others that fishing pressure should be increased on carnivores and more herbivores be injected to the environment to prevent the collapse of the fisheries.