The present investigation aims to illustrate the morphological, histological and ultrastructural differences in the intestine of a carnivorous fish, Schilbe mystus and a herbivorous fish, Labeo niloticus, in correlation with their feeding
habits. The histological examination of the mucosa of the intestine of both studied species revealed that it is built up of a simple columnar epithelium that contains goblet cells. Though these, are generally more numerous in the intestine
of Schilbe mystus than in that of Labeo niloticus. The ultrastructural investigation of the mucosa of the duodenum and ileum of Schilbe mystus revealed that the enterocytes are tall columnar cells and possess well-developed
microvilli, numerous mitochondria, microtubules and numerous lipid droplets. The ultrastructural examination of the mucosa of the ileum of Labeo niloticus revealed that the enterocytes are tall columnar and possess well-developed
microvilli, numerous mitochondria, microtubules, a few endocytotic channels and aggregated chylomicrons. The enterocytes of the rectum of both studied species are tall columnar and are characterized by the presence of short and wellspaced microvilli, a well-developed vesiculotubular system, numerousmicrotubules and mitochondria. In addition, the rectal enterocytes of Schilbe mystus contain endocytotic vesicles. The intestinal muscularis of both studied
species is well-developed and built up of unstriated muscle fibres, which are arranged into two layers: an inner circular layer and an outer longitudinal one.The rectal muscularis of both studied species is thicker than that of the rest of the
intestine.