Population characteristics of Oreochromis niloticus (Linnaeus, 1758) in light of varying water quality conditions of adjoined Lakes Naivasha and Oloidien in Kenya

Nile tilapia Oreochromis niloticus (L.) is a recent re-introduction in Lake Naivasha and is one of the fish species that has crossed into Lake Oloidien. This study assessed and compared the population characteristic of O. niloticus under different physicochemical conditions of water in L. Naivasha (main) and L. Oloidien. Samples of water for selected water quality parameters and fisheries data from catch survey were collected between 2017 and 2018. Results indicate the highest conductivity levels recorded in 2018 as 2916 ±11.30 µScm-1 and 282.33 ± 4.33 µScm-1 for L. Oloidien and L. Naivasha respectively. Mean total lengths of O. niloticus were 19.1± 1.8 cm and 23.6 ± 2.9 cm for L. Oloidien and L. Naivasha respectively. Mean weight of O. niloticus was 129.3 ± 37.8 g in L. Oloidien and 260.9 ± 81.0 g in L. Naivasha. Length-weight relationship analysis showed a negative allometric growth (b = 2.526) and (b = 2.983; p > 0.05) in lakes Oloidien and Naivasha respectively. The relative condition factor (Kn) values were slightly lower in O. niloticus from L. Oloidien compared to the main Lake. Differences between the two lakes in the population characteristics of O. niloticus may be attributed to the observed differences in the habitat conditions, including the conductivity and pH levels.