STRUCTURAL AND FUNCTIONAL CHARACTERISATIONS OF THE MOUTH AND OESOPHAGUS IN RELATION TO DIET IN HERBIVOROUS AND CARNIVOROUS RED SEA FISHES

The current study aimed to conduct a comparative analysis of the anatomical and histological characteristics of the upper digestive tract in two Red Sea fish species: the carnivorous grouper (Epinephelus coioides) and the herbivorous Longnose parrotfish (Hipposcarus harid). The current study was conducted on twenty fish of each species, collected from the Red Sea coast in Jazan region. The anatomical features of the oesophagus of the two species were investigated. Samples from the mouth and oesophagus were fixed in 4% paraformaldehyde and processed for histological investigation. The digestive tracts of both fish species start with the oral cavity, which is characterized by a wide mouth opening and very fine, tapering teeth in the Grouper. However, the mouth opening in Harid fish had distinctive beak-like jaws, in which the upper jaw teeth were fused. In both species, the oral cavity leads to the pharynx and oesophagus. The pharynx of Harid had a special set of teeth plates arranged in two rows and is called the pharyngeal mill. The oesophagus of the Grouper was a simple distensible muscular tube; however, in Harid, it was formed of three tubes that fuse before joining the intestine. The esophageal wall of both species was characterized by thick muscular layers and highly branched mucosal folds. The carnivorous grouper (Epinephelus coioides) exhibited significantly thicker esophageal mucosal, submucosal, and muscular layers compared to the herbivorous Longnose parrotfish (Hipposcarus harid). In conclusion, a direct correlation was found between the structure of the upper digestive system and the feeding ecology of these species.