Scanning electron microscopic studies of gill arches and rakers in relation to feeding habits of some fresh water fishes.

Abstract: The surface ultrastructure of the gill arches and the gill rakers of the three concerned species Oreochromis niloticus, Chrysichthys auratus and Clarias gariepinus was investigated by scanning electron microscopy. These structures show significant adaptive modifications associated with the food and feeding habits of these fishes. Short and tuberous type gill-rakers in O. niloticus, are a well interesting filter of food. In C. auratus gill rakers were short with broad base, they serve to strain water which was to bathe the gills and prevent any solid particles from passing over it. Gill rakers in C. gariepinus were long, cylindrical in shape and arising at acute angles to the arch, they help to strain food and other materials, thus protect gill filaments from damage. Prominent epithelial protuberances on the gill rakers and gill arches enable the taste buds, located at their summit, to project well above the surface of the epithelium. This could increase the efficiency of the taste buds in selective sorting of palatable food. Co-occurrence of teeth and taste buds on the epi-and hypopharyngeal bones (Types I–III) denotes that food processing and gestation occur simultaneously in the pharynx. Caniform, villiform and papilliform teeth on the epi- and hypopharyngeal bones of the three studied species respectively in O. niloticus, C. auratus and C. gariepinus were associated with a complex food-processing cycle. Mucous secretions, oozing through mucous cell openings, provide lubrication facilitating smooth passage of food through the pharynx. [Copyright &y& Elsevier]