Cichlid trophic morphology in the Cross River reflects ecological adaptation to diverse feeding strategies and habitat conditions

Objective This study investigated the ecomorphological variation and trophic specialization of cichlid species in the Cross River, Nigeria, to understand how morphology, diet, and habitat interact to drive ecological diversity. Methodology Eight cichlid species were sampled from three sections of the Cross River (upper, middle, and lower reaches). Morphometric traits (e.g., standard length, gut length, gape width) were measured and analyzed using Principal Component Analysis (PCA) and Discriminant Function Analysis (DFA). Stomach content analysis was conducted to assess dietary composition, and trophic guilds were defined. Canonical Correspondence Analysis (CCA) was used to explore relationships between morphology, diet, and environmental variables such as dissolved oxygen, substrate type, and vegetation cover. Results Morphometric traits differed significantly among species, with Oreochromis niloticus having the highest standard length (145.2 mm) and Sarotherodon melanotheron exhibiting the longest gut length (190.2 mm). PCA revealed that PC1 explained 47.8% of total variance, primarily influenced by standard length and body depth, while DFA showed a 65.1% separation among species based on trophic traits (Wilks’ λ = 0.324, p < 0.001). Diet analysis revealed that detritus (IRI = 6590.4) and algae (IRI = 3128.3) were dominant food items. Trophic guild classification identified omnivores, herbivores, insectivores, and detritivores, with omnivores showing the highest niche breadth (Levins’ index = 0.68) and trophic overlap (mean Pianka’s index = 0.74). CCA explained 68.5% of the variance in diet-morphology-environment relationships, confirming that species distributions were linked to environmental gradients and feeding adaptations. Conclusion Cichlid trophic morphology in the Cross River reflects ecological adaptation to diverse feeding strategies and habitat conditions. Morphological traits are strong predictors of diet and guild membership, and environmental factors further shape their ecological roles. These findings advance our understanding of functional diversity in African freshwater ecosystems and provide a reference point for biodiversity conservation in tropical riverine habitats.