Phenotypic Divergence Between Wild and Farmed African Catfish (Clarias gariepinus) in a Flood-Linked River System

African catfish (Clarias gariepinus) is an important aquaculture species in Nigeria, yet escapes from farms into natural rivers during seasonal flooding which raises concerns about potential mixing with wild stocks. This study aimed to assess the morphological variation between farmed and wild populations of C. gariepinus. Farmed specimens were collected from the University of Calabar Fish Farm, while wild individuals were obtained from the adjacent Great Kwa River. A total of 120 fish (60 from each population) were analyzed using 25 morphometric characters and 5 meristic traits. After size-standardization with Elliott’s allometric method, descriptive statistics showed that farmed fish were larger in standard length (28.7 ± 2.3 cm; range: 24.5–33.1 cm) compared to wild fish (25.4 ± 2.1 cm; range: 21.3–29.8 cm). Body depth was also greater in farmed fish (7.6 ± 0.7 cm) than in wild fish (6.3 ± 0.6 cm). Conversely, wild fish had relatively longer head length ratios (26.4% of SL) compared to farmed fish (23.1% of SL). Meristic traits overlapped but showed slight shifts, with dorsal fin rays averaging 75–77 in farmed fish and 73–75 in wild fish. Principal component analysis explained 72.4% of total variance, with PC1 strongly associated with body depth and head length. Canonical variate analysis clearly separated populations (Mahalanobis distance=4.62, P<0.001), while UPGMA clustering grouped fish into distinct farmed and wild clusters. These findings confirm morphological divergence between cultured and wild C. gariepinus, shaped by environmental and rearing conditions. The study concludes that escapes of farmed catfish could alter wild stock structure, and recommends integrating morphometric and genetic monitoring to guide sustainable aquaculture and conservation.