Studies On Life History Strategies Of Labeobarbus Altianalis (Boulenger 1900) And Labeo Victorianus (Boulenger 1901) In River Kuja -Migori, Kenya

Abstract

Fish life history strategies are all the changes through which a fish passes in its development from birth to natural death. Life history comprise feeding, growth, reproduction, and migration. Life history strategies determine how fish populations respond to dynamics in their environment such as fishing and environmental perturbations. The present study was done in River Kuja – Migori from January 2018 to June 2019. The overall objective was to describe life history strategies of Labeo victorianus and L. altianalis in River Kuja – Migori. The specific objectives were to determine the spatial and temporal distribution of L. victorianus and L. altianalis, correlate the abundance of L. victorianus and L. altianalis to physical and chemical parameters, determine spatial and temporal variation of condition factor, gonadosomatic index, fecundity, egg size, and determine temporal variation of the diets of L. victorianus and L. altianalis in River Kuja- Migori. Fish specimens were collected using an electrofisher from five sampling stations along River Kuja – Migori. The total length and weight of fish specimens were measured in centimeters and grams respectively. The fish were dissected to reveal their gonads, which were weighed, and the data obtained was used to calculate gonadosomatic index. A small proportion of the ovary was excised out, weighed and the eggs in the ovary teased out, counted then used to estimate fecundity. Selected physical and chemical parameters were determined using standard methods according to American Public Health Association, (2000). Population dynamic parameters were estimated using Fish Stock Assessment Tools software. There were significant differences in the spatial and temporal distribution of L. victorianus and L. altianalis (p < 0.05). Condition factor, gonadosomatic index, and fecundity significantly varied spatially and temporary (p < 0.05). Results on sexual maturity revealed that both L. victorianus and L. altianalis males attain sexual maturity earlier than females. The length at 50% maturity of L. victorianus was estimated at 18 cm and 20 cm total length for males and ix females respectively while in L. altianalis it was estimated at 16.3 cm and 18 cm total length for males and females respectively. Fecundity ranged from 47,842 - 101,902 eggs (mean = 83,663 ± 2605) in L. victorianus and 1320 - 2382 eggs (mean = 1552 ± 23.3) in L. altianalis. The mean egg diameter for L. victorianus was 0.65 ± 0.002 mm and 1.2 ± 0.007 mm for L. altianalis. There were no significant differences in sex ratio from the hypothetical 1:1 (χ 2 , p > 0.05) for both species. The results showed that L. victorianus has a longevity of 6 years while L. altianalis can live to a maximum of 9 years. The instantaneous growth rate (K) was estimated to be 0.25 yr-1 and 1.0 yr-1 for L. victorianus and L. altianalis respectively. The length-based growth performance indices were 2.86 yr-1 and 3.03 yr-1 for L. victorianus and L. altianalis respectively. Feeding habits of both species showed a shift in preference of food items from juvenile to adult. The results indicated that both species are omnivores mainly feeding on invertebrates during their juvenile life and detritus and plant material, during their adult life. Results showed that there could be competition between the two fish species on similar food resources in the river, both feeding exactly on the same type of food items. This study provides useful information for the formulation of management advice for L. victorianus and L. altianalis fisheries in River Kuja Migori