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Trophic Ecology of the Reed Fish, Erpetoicthys calabaricus from a Niger Delta Creek, Nigeria

Background and Objective: Considering the “near threatened” status of E. calabaricus, consequent upon habitat degradation from anthropogenic perturbations and total lacuna of literature and data on the trophic biology of the species, there was dire need to research on this aspects of its ecology. Thus, this study was carried out in other to compute data on food and feeding habits if the species. Materials and Methods: Six hundred and thirty four specimens were analyzed. Fish samples were obtained by sampling bi-monthly between April, 2013 and March, 2014. Samples were immediately preserved in 10% formalin solution for laboratory analysis. To evaluate feeding activity of E. calabaricus, the “points” method and gut repletion index (GRI) were used. Each intestinal bulb was assigned a number of points proportional to its degree of fullness according to an arbitrary 0-20 scale. Thus 0, 5, 10, 15 and 20 points were scored for empty, 1/4 full, 1/2 full, 3/4 full and full intestinal bulbs, respectively. Intermediate points were also scored where necessary. Mean point per gut, i.e., average gut fullness (AGF) was then calculated. The percentage occurrence of non-empty gut was computed to show the GRI. The gut contents of each specimen were dispersed with few drops of water in a Petri-dish and examined macroscopically with the naked eyes and microscopically under a dissecting microscope. The food items were sorted and identified to the lowest taxon possible with the aid of standard keys and descriptions. The relative importance of the dietaries was assessed by the points and frequency methods. Volume of gut fullness was shared among the gut contents in units proportional to their bulk (estimated visually). The total points per food item were then expressed as a percentage of grand total points scored by all food items. Results: The gut contents revealed that 10 food items were ingested and categorized into 6 major groups viz Algae, Crustacea, Insecta, Nematoda, Pisces and Detritus. Algae comprised blue green algae (Annabella sp.). Crustaceans consisted of Macrobrachium sp. and shrimp remains. Insecta included diptera, coleoptera and insect remains. The Nematoda group consisted of earthworm and its remains. Pisces included fish remains (bones and scales). Detritus was made up of coarse particulate organic matter (CPOM) and fine particulate organic matter (FPOM). Food ponderance index (FPI) showed that E. calabaricus fed primarily on insecta (44.70%), crustacea (39.13%) and worms (15.15%) as dominant food items, while Algae (0.41%), pisces (0.60%) and detritus (0.01%) were ingested as incidental items. Conclusion: Findings suggests that the high relative importance and abundance of insects, crustaceans and Nematoda in diets of the fish suggests invertivorous foraging with narrow trophic spectrum.