الفهرس 
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Abstract
It was found that mucosal layer in the anterio-middle region is thicker than in the posterior region of the oesophageal wall of the fish species studied except in C. auratus.
Thickness of muscularis layer in the anterio-middle region is larger than in the posterior region of the oesophageal wall in the fish species studied.
Mucosal layer of the stomach of C. auratus in the middle region is thicker than that of the anterior and posterior regions. In M. kannume, the mucosal layer of the stomach in the anterio-middle region is thicker than that of the posterior region. In S. schall, mucosal layer of the stomach has the same thickness in the two regions.
Mucosal layer in the intestinal wall in the anterio-middle region is thicker than that of the posterior region in B. bynni and S. schall . Mucosal layer in the middle-posterior region is thicker than that of the anterior region in C. auratus. Mucosal layer in the posterior region of intestine is thicker than that of the anterio-middle in M. kannume.
2. Histology
The oesophageal wall has the same structure in fishes under study except absence of oesophageal glands in B. bynni.
The results of the present study revealed that C. auratus, M. kannume and S. schall showed almost the same structures in the different regions of the stomach with the exception of the absence of gastric glands in S. schall.
Using PAS –AB reaction, there was distinct goblet cells through the mucosa of the intestinal wall. The mucous cells (goblet cells) are numerous in the posterior region than in the anterior one.
3. Scanning electron microscope
There are no teeth recorded in the anterior region of the roof and the floor of B. bynni, the superior and inferior pharyngeal teeth of this fish were rounded in shape. All teeth of the carnivorous C. auratus were pointed canine-like teeth. Carnivorous M. kannume has two kinds of teeth; the 1st form was molariform teeth and the 2nd form was pointed canine-like teeth. Omnivorous S. schall has four kinds of teeth; the 1st form was pointed canine-like teeth, the 2nd form was curved and have blunt surfaces, the 3rd form was more curved and pointed and the 4th form was short and conical in shape.
In the present work, two types of taste buds (type I and type II) were recorded in the pharyngeal cavity of B. bynni, (type I and type III) were observed in C. auratus and M. kannume and (type I, type II and type III) were recorded in S. schall.
There are some different patterns of mucosal folds throughout the digestive tract, concerning oesophagus, stomach and intestine of fish under study.