Effect of Climate Change on Morphological Divergence and Species Discrimination in Cichlids from the Cross River, Nigeria

Morphological divergence and species discrimination are essential for understanding freshwater fish biodiversity but remain underexplored in African river systems. This study analyzed 480 specimens from eight cichlid species in Nigeria’s Cross River using morphometrics, principal component analysis (PCA), and discriminant function analysis (DFA). Standard lengths ranged from 9.07 ± 0.11 cm in Sarotherodon melanotheron to 15.27 ± 0.27 cm in Oreochromis placidus. The first two PCA components explained 59.9% of total morphological variation, with standard length, dorsal fin depth, and caudal fin length identified as key contributors. DFA indicated that caudal peduncle depth plays a crucial role in swimming efficiency. O. niloticus and O. placidus exhibited the closest morphological affinity (Mahalanobis distance: 1.14), while O. niloticus and Coptodon dageti were the most divergent (12.71). Regression analysis showed that standard length was positively associated with water temperature (β = 0.42, P < 0.001). Scenario-based projections suggested that climate change could increase standard length by up to 4.8% in O. niloticus and reduce body depth by 7.2% in S. melanotheron. These findings offer new insights into the ecological roles and evolutionary dynamics shaping cichlid diversity in the Cross River. They also highlight the urgent need for adaptive conservation strategies to protect these species amid changing environmental conditions. A key recommendation is the implementation of long-term monitoring and habitat management programs targeting vulnerable and specialized cichlid populations.