Distribution, Growth and Mortality of Labeobarbus altianalis of River Kuja, Lake Victoria Basin, Kenya.

Abstract

This study was conducted with the major objective of investigating the distribution, growth and mortality of Labeobarbus altianalis in River Kuja which is one of the major rivers draining into Lake Victoria. So far, limited research has been undertaken on the biology and ecology of the species in the Lake Victoria basin, particularly in the riverine environments. A total of 1486 fish specimens were collected monthly at six sampling sites along River Kuja from November 2016 to August 2017 using an electrofishing equipment. The length and weight of the fish were measured then separated into males and females to obtain sex ratio and dissected for sexual maturity examination. Monthly length-frequency distributions of L. altianalis were analyzed using the FiSAT computer software to estimate growth parameters, recruitment pattern, mortality, exploitation rate and longevity of the species. This data was augmented with information on the physical and chemical characteristics of the sampling point along the river for use in explaining the distribution pattern of the species. The asymptotic length (L∞) and growth coefficient (K) were estimated as 60.00 cm TL and 0.40 yr-1 respectively using the ELEFAN method, while the Powel Wetheral method provided an L∞ of 61.29 cm TL and a ratio of total mortality to growth coefficient (Z/K) of 2.80. The length at 50% maturity for the female and male were 38.33 cm and 33.33 cm TL respectively. The exploitation rate, growth performance index and potential longevity were 0.61, 3.16 and 7.5 years respectively. The total, natural and fishing mortality were 1.83 yr-1, 0.71 yr-1 and 1.12 yr-1 respectively. The fish recruits twice a year November to January and April to July. The results indicate presence of L. altianalis in the Kuja River though 81.03% constitute fish that are sexually immature. The species is naturally recruiting and is able to grow to an age of reproduction. The knowledge gained will be useful for management purposes since it acts as inputs for formulating the models used for sustainable management. The management will ensure the growth of the immature fish and conserve the L. altianalis populations of River Kuja.