Anatomical and histological adaptations of digestive tract in relation to food and feeding habits of lizardfish, Synodus variegatus (Lacepède, 1803)

The adaptations in anatomical and histological structures of the digestive tract of fish are correlated with their food and feeding habits. An understanding of these habits is essential to emphasize the related functional mechanisms of fish digestive physiology. Little is known about the adaptations of the alimentary tract of coral reef fish to food and feeding strategies in the Egyptian Red Sea. The present study investigated the anatomical and histological structure of the digestive tract of the lizardfish, Synodus variegatus. The results indicated that the oesophagus in S. variegatus is a short, narrow and distensible muscular tube, that is adapted to conduction of food. The mucosa is composed of a thin stratum of simple columnar epithelium opens to the lumen and a thick layer of mucous tubular glands located at the base in both the anterior and posterior oesophagus. The muscular layer is formed of one circular layer. The stomach has a great distensibility with a bag-like shape to enable the fish to swallow relatively huge preys. Further, it has numerous gastric glands in the cardiac portion for food digestion. As for the pyloric portion, it is a very dense layer of muscularis, which contributes in regulating the passage of digested food to the intestine. The relative length of gut ranges from 0.67 to 0.73 cm with an average of 0.7 ± 0.02 cm. The intestine is a short uncomplicated tube. The mucosal folds in the anterior intestine are very long, numerous and with round tips. Such structures are shorter and fewer in number towards the mid intestine, and much thicker and blunt in the posterior intestine. The epithelial lining of the intestine consists of columnar cells for absorption, and numerous large goblet cells for the lubrication of feces. Finally, based on the findings of the anatomical and histological investigations, it may be concluded that there is a correlation between the adaptations in the digestive tract structure of the lizardfish, S. variegatus, and their feeding habits. Keywords: Adaptations, Alimentary canal, Histoarchitecture, Lizardfish, Morphology