Ichthyofauna variety of Lake Asejire: natural implications

Abstract

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.