Abstract

This study assessed the diversity and abundance of fish species in the River Benue over an 18-month period (January 2020 to June 2021), spanning dry and wet seasons. Fish sampling was conducted monthly at three sites: Lau (Site A), Mayo-Ranewo (Site B), and Ibi (Site C), using gillnets of varying mesh sizes (60, 70, 80 and 90 mm) across different habitats. A total of 54,774 fish, representing 17 families and 39 species, were recorded. Mormyridae exhibited the highest diversity (20.77%, eight species), followed by Cichlidae (16.94%, four species) and Alestidae (14.41%, five species). Dominant species included Oreochromis niloticus (4.96%), while Polypterus senegalus (0.24%) was the least abundant. Fish abundance was higher during the dry season (32,353 fish) compared to the wet season (22,421 fish). Site B consistently recorded the highest abundance across seasons, while Site A exhibited the most significant seasonal decline. Biodiversity indices, including the Shannon-Weiner diversity index (H’), showed slight seasonal variation, with higher values in the wet season at Site B (H’ = 3.581). Evenness was highest at Site A in the wet season (E = 0.848), indicating uniform species distribution. The results highlight seasonal and spatial variations in fish diversity and abundance, emphasizing the ecological significance of the River Benue’s fish communities.

Key Words: River Benue, Fish diversity, Fish abundance, Seasonal variation