الفهرس 
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Abstract
Summary
The present work was carried out on 40 specimens of both sexes of catfish (carnivorous fish) and grass carp (herbivorous fish) in order to observe the morphological and histological differences between the two species. The results of the present work were revealed some differences in structure of the gastrointestinal tract related to type of food and feeding habits of each species.
The present results showed that the length of gastrointestinal tract of carp was twice as the standard length of the body. The gastrointestinal tract as well as the intestine of grass carp were increased significantly (P < 0.01) in length as compared to those in catfish, which may help in retention of food for a longer period of time to ensure proper digestion. Also, the percent of relative gut length (RGL) of grass carp was approximately twice as compared to that in catfish. This phenomenon could be supported by the demonstration of large diameter of intestine of grass carp required for increase the storage capacity of food.
The gastrointestinal tract of catfish was consisted of oesophagus, stomach and intestine (anterior, posterior intestine and rectum), while that of grass carp was consisted of oesophagus, intestinal bulb and intestine (anterior, posterior intestine and rectum).
Oesophagus of catfish was divided into 2 parts; anterior and posterior ones. The current observations revealed that the anterior part of oesophagus of catfish was characterized by presence of numerous mucosal folds, that may allow maximal distention for prey and broken down of food and it was lined by stratified epithelium with goblet cells. In addition to club cells, which appeared as large acidophilic cells between the lining stratified epithelium. The transmission electron microscopic observations revealed that the club cells showed presence of rER, free ribosomes, mitochondria and many vesicles, which contained electron dense secretory materials that might be responsible for induction of the fright reaction to other fish.
Scanning electron microscopic examination of the oesophageal epithelium of catfish demonstrated presence of microvilli in the superficial cell layer that indicates an adaptation to rapid ion absorption. While the presence of fingerprint- like microridges in oesophageal epithelial cells of catfish may represent a mech