Analysis of some biological aspects of the Blue-spotted tilapia, Oreochromis leucostictus (Trewavas, 1933) in Lake Naivasha, Kenya

Abstract

Oreochromis leucostictus is one of the commercially important tilapiine in Lake Naivasha. Its stock in the lake has declined due to the effect of fishing and pollution. This study investigated on its length-weight relationship, condition factor, sex ratio and maturity. Fish samples (233) were caught using gillnets of mesh-sizes 2-5 inches. Each individual fish was measured (cm) and weighed (g) in the field. The specimens were preserved in ice and transported to the laboratory for analysis of maturity. The mean (±SE) total length and weight for all fish was 21.3±0.3 cm TL and 187.4±8.3 g, respectively. Males 22.3±0.4 cm were significantly larger than females 19.2±0.5 cm. The mean condition factor was 1.06, 0.99 and 1.04 for male, female and combined sexes, respectively. The overall population sex ratio was 2.19:1.0 (male: female) that deviated significantly from 1:1. The slope b of the length-weight relationship was 1.92, 3.07, 2.33 for males, females, and combined sexes, respectively. Length at 50% maturity was estimated at 21.0 cm for females and 26.0 cm for males. Ripe oocytes and testis were found in all fish sizes. Comparisons with earlier studies suggest that the parameters of its growth, condition and maturity vary greatly from the different habitats.