Population Structure and Breeding Biology of the Nile Tilapia (Oreochromis niloticus) in Jebba Reservoir, Kwara State

This study examines the population structure and breeding biology of Oreochromis niloticus in Jebba Reservoir, Kwara State, located in Nigeria's North Central geopolitical zone. Oreochromis niloticus is the dominant commercial fish species in the reservoir and supports a substantial artisanal fishery, but current knowledge of its population dynamics in Jebba Reservoir is insufficient to support evidence-based fisheries management. Monthly fish samples were collected over eight months using gill nets of varying mesh sizes at three stations. Length-weight relationships, condition factor, sex ratio, length at first maturity, gonadosomatic index, and fecundity were determined from 280 specimens. Growth parameters were estimated using the von Bertalanffy growth function. Results revealed a slightly negative allometric growth pattern (b = 2.87) with mean condition factor of 1.42, indicating good nutritional status. The sex ratio was significantly skewed toward females (1:1.62, female to male). Mean length at first maturity was 18.4 cm total length. Gonadosomatic indices peaked between April and June, indicating a principal spawning season at the onset of the wet season. Mean absolute fecundity was 1,840 eggs per female. Exploitation rate estimates suggested moderate overfishing pressure at the midstream station. The study recommends minimum mesh size regulations of 7.5 cm, seasonal fishing restrictions during peak spawning months, and regular monitoring of length-frequency distributions in Jebba Reservoir. Keywords: Oreochromis niloticus, population structure, breeding biology, Jebba Reservoir, fisheries management.