Fish exploit the diversities of food organisms and habitats in their aquatic environments according to their structural morphology and feeding habits, hence its ecological roles and functions. Six morphological measurements and dietaries of 582 stomachs of eleven (11) species in the Cross River estuary, Nigeria, were examined from August-December, 2014 to establish interrelationship of diet and morphology. TrophLab® estimated the trophic level (Tl) for each species. Dietaries reveal 3 to 11 food items on which basis species were grouped into three functional trophic guilds: omnivore (6 species), detritivore-algivore (2 species) and carnivore (3 species). Positive linear relationship was established between total length (TL) and mouth area (MA) (r = 0.31 – 0.96; p < 0.5; r2 > 0.5 in Cynoglossus senegalensis and Liza falcipinnis, r2 < 0.5 for other species) except in the cichlid Ethmalosa fimbriata (r = 0.000267; p = 0.9997). Higher relationships were established in mouth area (MA) and mouth dimensions (MV and MH) with trophic levels (Tls) among species within same trophic guild than when non-related species were combined: detritivore (r2 = 1.00), carnivore (r2 = 0.91), omnivore (r2 = 0.4348), and all species combined (r2 = 0.1414). Cluster analysis reveal a positive trophic correlation whereby species of similar feed habits tend to exhibit similar diet-morphology traits than unrelated species. The canonical correspondence analysis reveal some level of morphological convergence in diet-morphological relationships, particularly, in traits like body depth-body height (BD/BH), mouth area and mouth area – trophic level (MA/Tls) and eye diameter (ED) among species. This study suggests trophic levels and mouth dimensions for similarly-sized samples of some species for which no information is available on their feeding habits could be estimated based on fish morphology of the species in study area.
Keywords: Food Web, Quantitative and Qualitative Trophic Connections, Trophlab
