Assessment of Fish Species Diversity and Abundance in the Rima River, Sokoto State

The Rima River in Sokoto State, North West Nigeria, is an important inland fisheries resource for riparian communities, yet current documentation of its fish biodiversity is limited to older surveys that predate recent environmental changes in the basin. This study assesses the fish species diversity, relative abundance, and seasonal variation in the Rima River at three sampling stations, one near Sokoto town and two in more remote upstream sections, over a five-month period. Fish were sampled using a combination of gill nets, cast nets, and fish traps deployed at each station biweekly. Physicochemical parameters were measured concurrently. A total of 29 fish species belonging to 16 families were recorded. Cichlidae, Mochokidae, and Cyprinidae were the most species-rich families. Species richness and abundance were highest at the upstream station with least anthropogenic disturbance. Catch per unit effort was significantly lower at the station downstream of the urban section of Sokoto, consistent with the impacts of wastewater discharge and fishing pressure. Three species of previously documented occurrence, including Heterotis niloticus, were absent from all catches, raising concern about local population decline. The dry season saw reduced species richness and catch, reflecting the effects of reduced water volume. The study provides an updated fish biodiversity baseline for the Rima River and recommends the establishment of a closed season and minimum mesh size regulation for this fishery under Sokoto State fisheries law.

Keywords: fish diversity, Rima River, species abundance, artisanal fisheries, Sokoto State