Contributions to the reproductive biology of Tllapia Cabrae (Boulenger 1899) from a small lake in Imo State, Nigeria

Abstract

This study focused on some aspects of the reproductive biology of Tilapia cabrae of UmuoseJiche lake, a man-made lake in Imo State, Nigeria. Basic somatic characteristics such as male: female sex ratio, gonadosomatic index, breeding cyclicity and fecundity were determined. The relationship between total length, standard length, body weight, gutted weight and  ovarian weight were estimated from the simple linear regression model F = al3• Males were dominant in the samples i n ApJiI, June, July, and December (2001 ) while females were dominant in the month of March (2002). Total male: female ratio was 1 :0.57, with a bias in favour of males. There was a preponderance of males in 5 of the different size g roups vis: 70 80 mm (n=55), 1 30 1 40 mm (n=89), 1 40 1 50 (n=67), 1 50 1 60mm (n=80) and 1 60 1 70mm (n=70) while females were dominant in only the 1 20 1 30mm (n=58) size group. The mean ovarian weight for the fish was 0 .46 ± 0. 1 8g (n=645) and the mean gonadosomatic index was 0. 9±0.33 (n=645). The ovaries bear an average of 791 ±402 (n=645) eggs per spawn. Fecundity was positively and linearly correlated with total length, standard length, gutted weight and body weight.

Key words: Tilapia cabrae, fecundity, gonads, ovarian weight, Umuoseriche Lake, Nigeria