Growth, mortality and recruitment of Nile tilapia (Oreochromis niloticus) (L.) (Cichlidae) in Lake Turkana (Kenya): Possible variations as assessed by length frequency analysis.

Abstract

Estimates of growth, mortality and recruitment pattern of Nile tilapia iOreochromis niloticus) from Lake Turkana were obtained from two sets of length frequency distributions: one from HOPAON (1982) obtained in 1974 from littoral beach seining and a recent one obtained from multi-mesh size gill net fished from April 1989 to November 1991. Data analysis was performed with the FISAT (FAO ICLARM Stock Assessment Tool, version 1.0) software. Values of Lao = 40 and 59.5 (em TL), and K = 0.250 and 0.325 yr'; and the ratio of total mortality rate to the growth constant (ZlK) of 2.72 yr 5.11 y'" were obtained respectively with a clear seasonal growth pattern. The total mortality estimates from the catch curve analysis were Z = 0.96 and J .59 yr respectively with a natural mortality (M) of about 0.65 yr' for a mean environmental temperature (T) of 27°C. The highest peak for recruitment was from June to September indicating recruitment of one cohort per year. The growth performance index (0) = LoglO + 2 LoglO L"" = 2.57 and 2.87 for the two sets of data respectively. These results are discussed and compared to available information on growth performance index for Oreochromis niloticus in other large African Lakes