Comparative histochemical study of the gastrointestinal tracts of the Nile tilapia (Oreochromis niloticus) and the hybrid catfish (Clarias batrachus x Clarias gariepinus).

Because of the wide variety of cells which are arrayed in the tissue of the gastrointestinal tracts of these two fish, basic histological examination is not appropriate to clarify the histological structure. But histochemical techniques can be applied to identify the chemical differences contained in the tissues. The present study aimed to compare the histochemical characteristics of the gastrointestinal tracts of adult fishes which consume different types of food: the Nile tilapia is herbivore and the hybrid catfish is carnivore. The esophagus, stomach and intestine of each fish was stained with 1) Masson's trichrome, for the muscular and connective tissues, 2) Periodic acid Schiff, for neutral mucin, 3) Alcian blue pH 2.5 and pH 1.0, for acid and sulfated acid mucin. The neutral and acid mucins were observed in the esophagus of the tilapia and catfish but sulfated acid mucin was found only in the catfish. Both neutral and acid mucins presented in the stomach of the tilapia, whereas the stomach of the catfish contained only the neutral mucin although it is contained more collagen in the submucosa. The tilapia intestine revealed that neutral and acid mucins were presented throughout the tissue, and small amounts of sulfated acid mucin were observed in the anterior intestine. However, sulfated acid mucin was very obviously located in posterior intestine of the catfish. Moreover, all parts of the catfish intestine showed both neutral and acid mucins with a thick collagen layer in the submucosa. This research will be useful for understanding the physiology of the relevant digestive systems and making a diagnosis of some gastrointestinal diseases in these two fish.