Ecological status, and conservation implications of fish assemblages in Tagwai Dam, Niger state, Nigeria

This study presents the first comprehensive assessment of the taxonomic diversity, ecological status, and conservation implications of fish assemblages in Tagwai Dam, Minna, Niger State, Nigeria. A total of 11 fish species from 7 families and 5 orders were identified, with Cichlidae being the most diverse (45% of taxa). Dominant species included Oreochromis niloticus (24.81%), Brycinus nurse (22.20%), and Coptodon zillii (15.43%), collectively accounting for over 62% of total catch. Species richness was relatively low, and rare species such as Labeo senegalensis (0.64%) and Mormyrus hasselquistii (0.25%) occurred in very low proportions. Twelve, monthly gillnet surveys were conducted across five spatially distributed sampling sites. Diversity metrics revealed a Shannon-Wiener Index (H?) of 1.971, Simpson’s Dominance Index (D = 0.165), and Evenness (E = 0.82), indicating moderate diversity but dominance by a few species. A one-way ANOVA showed significant spatial variation in species abundance (F = 4.32; p = 0.003) but no significant seasonal variation (F = 0.521; p = 0.670). The presence of highly dominant invasive tilapias (O. niloticus, C. zillii, and S. galilaeus) highlights the ecological simplification and potential threat to native taxa. Compared to other Nigerian reservoirs (Kainji, Oyan), the dam supports moderate diversity under stress. The findings call for urgent management action, including invasive species control, fishing regulation, habitat restoration, and long-term ecological monitoring to sustain the dam’s biodiversity and fishery productivity.