This study aims to illustrate the histological, histochemical and ultrastructural differences in the ileum of a carnivorous fish, Clarias gariepinus and an herbivorous fish, Oreochromis niloticus in correlation with their feeding habits. Twenty live O. niloticus and C. gariepinus were collected from Nile River. After capture, they were capitated; the entire digestive tract was removed from the body. The small intestine was separated and then cut into three parts; the ileum was separated and examined. The histological characterizations revealed that the wall of the ileum in both species is composed of four layers; Tunica mucosa, Tunica sub mucosa, Tunica muscularis and Tunica serosa in O. niloticusis while Tunica adventitia in C. gariepinus. The mucosal surface forms numerous elongated compact folds called villi lined by enterocytes and number of goblet cells. The muscularis layer is thicker in C. gariepinus compared to O. niloticus. Histochemically, goblets cells in both species show positive affinity to the stain, but it is more intensive in C. gariepinus. TEM of the mucosa layer of the ileum of both species revealed that villi lined with basal enterocytes covered with apical microvilli, goblet and granular cells which appeared abundant in C. gariepinus compared to O. niloticus. Finally we concluded that there are differences between two studied species according to their feeding habits.
Key words: Clarias gariepinus -Histology- Oreochromis niloticus -TEM
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