Journal of Biology and Nature

The reproductive biology of Oreochromis niloticus was investigated in the Zienkôlô dam lake, northern Côte d’Ivoire, from December 2024 to November 2025. Reproductive parameters of O. niloticus were determined with the aim of ensuring rational and sustainable management of the resource. A total of 351 specimens, comprising 129 females and 222 males and ranging from 6.5 to 22.5 cm in total length, were examined.  The various specimens were collected monthly using gillnets. Sex ratio, size at first sexual maturity, gonadosomatic index, hepatosomatic index, condition factor, and monthly changes in sexual maturity stages were assessed. Males were numerically dominant, with an overall male-to-female ratio of approximately 1:0.58, which differed significantly from the theoretical 1:1 ratio (χ² = 24.64; p < 0.05). The estimated size at first sexual maturity was 11.81 cm total length for females and 14 cm for males, indicating that females attained maturity at a smaller size. The condition factor varied between 1.52 ± 0.02 and 2.07 ± 0.17. Analysis of female maturity stages and monthly gonadosomatic index variation indicated reproductive activity throughout the annual sampling period. Gonadosomatic index values showed prominent peaks in May and October, suggesting periods of increased reproductive activity. Hepatosomatic index variation generally followed the reproductive cycle, while the condition factor varied across months. These findings provide baseline information on the reproductive characteristics of O. niloticus in the Zienkôlô dam lake and may contribute to future evaluation and management of the local fish population.