Asian Journal of Current Research

This study examined aspects of the biology of Oreochromis niloticus, focusing on sexual dimorphism within the Qua Iboe River Estuary, Nigeria, from April 2021 to March 2022. A total of 1,267 specimens were obtained from artisanal fishers using various mesh sizes of gill nets and cast nets. Sex identification was based on genital papilla morphology, with males possessing a single opening and a distinct genital papilla, while females exhibited two openings. Additional dimorphic features included pointed dorsal and anal fins in males and rounded, more expanded fins in females. The overall population consisted of 689 males (54.38%) and 578 females (45.62%), yielding a male–female ratio of 1:0.83, which significantly deviated from parity (χ² = 87.299, df = 1, P < 0.05). Biometric characteristics showed minimal size dimorphism. Males recorded a mean total length of 12.08 ± 0.157 cm and mean total weight of 37.77 ± 1.10 g, while females measured 12.05 ± 0.11 cm and 35.66 ± 0.903 g, respectively. The condition factor (K) was slightly higher in males (2.14 ± 0.04) than in females (2.04 ± 0.03), indicating good physiological status across the population. Length–frequency distribution revealed that most individuals occurred within the 10–14 cm size class, suggesting strong recruitment, continuous breeding activity, and a stable, thriving stock. The findings provide essential baseline information on sexual dimorphism, population structure, and length–weight characteristics of O. niloticus in the Qua Iboe River Estuary. These insights are valuable for improving local aquaculture practices, enhancing broodstock selection, supporting sustainable fisheries management, and guiding conservation strategies for the species in Nigerian estuarine ecosystems.