Some Aspects of the Biology of Tilapia Zillii (Gervais) (Pisces: Cichlidae) in Opa Reservoir, Ile-Ife, Nigeria

Abstract

Some aspects of the biology of Tilapia zillii were examined between October 1997 and February 2000. Fish specimens were collected using a graded set of gillnets and castnets. Out of 1486 fish specimens, 867 were males while 619 were females. Regardless of their sex a significantly high number of fish were caught inshore (69.57%) than in the offshore areas (30.43%). In addition 48.65% of all fish specimens were caught in the middle segment of the reservoir. A wide range of fish sizes were caught and the species was not spatially distributed (χ²cal. 27.39<χ² tab. 67.51; df. 820). The species fed on a variety of food substances predominantly shoreline aquatic macrophytes, algae and plankton. The feeding rhythm which started around 6.00am reached a peak by 3.00pm in the afternoon and it declined gradually until 6.00pm.