Comparative morphological and histological studies on the adaptation of esophagus and stomach to the feeding habits in some coral reef fishes at Hurghada, Red Sea, Egypt

The present study deals with the morphological and histological adaptations of the esophagus and stomach of some coral reef fishes (Parupeneus forsskali, Popilloculiceps longiceps and Acanthurus sohal) and their feeding habits.
 Results showed that the esophagus of carnivorous fish, Parupeneus forsskali, piscivores fish, Popilloculiceps longiceps and herbivores fish, Acanthurus sohal is a short, narrow and distensible muscular tube to conduct the food. Owing to the esophageal mucosa of the three fishes is of a stratified type. The great distensibility of the esophagus is an adaptation for feeding. So a relatively large object can be swallowed. In the P. forsskali the mucosa containing large mucus glands. On the other hand in P. longiceps and A. sohal the mucosa is thrown into primary and secondary folds. The stomach of P. forsskali is sac-like in shape. While the stomach of P. longiceps is with a great distensibility giving the bag-like shape to enable the fish to take relatively huge prey. The stomachs of these species have a vast amount of gastric glands in the cardiac portion, while, in the pyloric one has a very thick layer of muscularis. The stomach of A. sohal is U shape. It can be divisible into cardiac and pyloric regions. Cardiac region is highly specialized as a masticator organ for the fish that eat hard vegetable matter. The epithelium of the pyloric stomach develops into a thin layer of columnar cells towards the lumen and a thick layer of gastric glands towards the base to help in  digestion.
In conclusion, the esophagus and stomach of carnivorous fish, P. forsskali, piscivores fish, P. longiceps, and herbivores fish, A. sohal are subjected to diverse and significant variations and much modification in accordance with the food type and feeding habits.