Length-Weight And Diet Composition Of Selected Teleost Fishes From Kilifi County, Kenya

Abstract

Sustainable exploitation of fishery resources requires knowledge of the population dynamics of the target resource. Studies have shown consistence and considerable decline in the densities and species richness of most coral reef fishes along the Kenya coast. Concerns over the sustainability of current fishing pressure on target fish species has led to recommendations on conducting population dynamics on those species. Fish were obtained from catches of artisanal fishers at three landing sites (Mtwapa, Kanamai and Kuruwitu) in Kilifi County between February and April 2017 in order to determine their length-weight relationship, condition factors and diet composition in two species. The fishers used spearguns, gill nets, basket traps, beach seines, monofilament nets using motor boats and dugout canoes. A total of 454 fishes were sampled, belonging to seven families, eight genera and nine species. Length-Weight relationship and relative condition studies were conducted on seven demersal species; Calotomus carolinus (Valenciennes, 1835), Decapterus macrosoma (Bleeker, 1851), Lethrinus nebulosus (Forsskal, 1775), Lethrinus harak (Forsskal, 1775), Lutjanus fulviflamma (Forsskal, 1775), Sargocenton caudimaculatus (Ruppel, 1838) and Siganus sutor (Valenciennes, 1835) and two pelagic species; Rastrelliger kanagurta (Cuvier, 1816) and Scomberoides tol (Cuvier 1832).There was a significant (p < 0.05) positive relationship between total length and body weight in all the fish sampled (r = 0.909 – 0.962) suggesting that the growth of fish length and weight is proportionate. The t-test calculated on b revealed no significant deviations (p > 0.05) from the expected cube value of 3 indicating no existence of cubic relationship between length and weight for the species. These fish species had relative condition factors above one, ranging between 1.0037 ± 0.053 to 1.0210 ± 0.089076 revealing that the nutritional requirements were available in the ecosystem for fish growth. The diet composition was determined for S. sutor and L. harak xiii because they had a relatively high market demand compared to the other fish species. The diet was established using frequency of occurrence and numerical method. Diet composition of S. sutor revealed that important food items consisted mainly of algae (Hypnea spp) and seagrass (Thalassodendron ciliatum) while in L. harak, crustaceans (crabs) and worms were abundant. The length-weight relationship of two species, C. carolinus and S. caudimaculatus are described for the first time in Kenya. The present length-weight relationship for the nine species could be used as a baseline tool for enhanced fisheries management in Kilifi. The assessed diets of S. sutor and L. harak could be used to attempt culture possibilities of the two fish species. However, more extensive research needs to be undertaken which would involve the standardization of sampling seasons and measurement of environmental physico-chemical parameters before additional inference could be made.