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Coptodon zilli and Micropterus salmoides were introduced into Lake Naivasha in 1929 and 1959 respectively. The reasons for introduction were to boost the fisheries and for recreational fishing respectively. However, the numbers of the two fish species in the lake have been declining over the years due to human activities and other ecological changes within the lake. Length-weight relationship, condition factor, sex ratio and length at first maturity of the fish were studied from October 2016 to November 2018. A total of 303 fish samples; 193 C. zilli and 110 M. salmoides were used in this study. Results showed that C. zilli and M. salmoides had an allometry coefficient value of 2.9 and 3.1 and K value of 1.77 and 1.39 respectively. The sex ratios (male: male) of C. zilli and M. salmoides were 1.1: and 1.3:1 respectively. The shortest total length for mature C. zilli and M. salmoides recorded were 12 cm and 26.5 cm while 21.8 cm and 51 cm were for the longest respectively. The fish growth pattern therefore failed to obey the cube low of b=3 thus exhibiting allomentric growth. The fish were in good condition with K factor above 1. It can therefore be concluded that the fish are generally in a good condition though the early maturity especially for C. zilli could be a sign of pressure either from environmental factors or as a result of overfishing within the lake. Investigations should be centered on breeding and population dynamics to better understand the two species within the lake.

Some aspects of fish growth in Redbelly Tilapia (Coptodon zilli) and Largemouth Bass (Micropterus salmoides) in Lake Naivasha, Kenya