Ecological Drivers Of Fish Communities In The Great Kwa River, Cross River State, Nigeria

Freshwater biodiversity in tropical rivers like the Great Kwa River, Cross River State, Nigeria, faces increasing pressure from urbanization and industrial pollution, yet detailed ecological assessments remain limited. This study aimed to investigate the ecological drivers of fish community structure along spatial and seasonal gradients of the Great Kwa River. Monthly fish samples were collected from three stratified stations between January and December 2024, alongside measurements of water physicochemical parameters, sediment quality, and macroinvertebrate assemblages. Results showed a total of 34 fish species belonging to 17 families, with Cichlidae (28.7%) and Clupeidae (15.4%) as the dominant groups. Species richness was highest at the upstream station (Margalef’s D = 4.07), which also had higher dissolved oxygen (5.8 ± 0.7 mg/L) and lower total hydrocarbon content (0.32 ± 0.08 mg/L). Midstream sections exposed to effluent discharge exhibited significantly lower fish diversity (D = 2.89), reduced macroinvertebrate richness, and sediment heavy metal levels exceeding WHO guidelines (lead: 0.59 ± 0.08 mg/kg; copper: 2.87 ± 0.16 mg/kg). Correlation analysis confirmed positive associations between dissolved oxygen and fish richness (r = 0.68, p < 0.01) and negative correlations between hydrocarbon content and fish diversity (r = –0.76, p < 0.01). These findings highlight the role of hydrological and anthropogenic factors in shaping fish communities and emphasize the need for improved wastewater management along the river. It is recommended that an integrated river basin management strategy be implemented to reduce pollution impacts and promote sustainable fisheries in the Great Kwa River.