HISTOLOGY OF THE DIGESTIVE SYSTEM IN CHEILINUS UNDULATES R躊PELL

This paper reported the histological studies of the digestive system of the humphead or Napoleon wrasse(Cheilinus undulates R黳pell) by light microscopy of tissue sections,and described the morphological features of the digestive system of this species.The humphead wrasse,a member of the family Labridac,is a species of stomachless and carnivorous fish.The digestive tract of these fish consists of oral-pharyngeal cavity,esophagus,small intestine,rectum and anus.Their jaw teeth and pharyngeal tooth in the oral-pharyngeal cavity are tough and strong.The intestine is short in length and wide in diameter,and curve-shaped.The average ratio between the length of the intestine and the body length is 0.43.Histological studies showed that the esophagus mucosa layer of the humphead wrasse was covered with wrinkles and folds.The submucosa,longitudinal muscle and circular muscle layers of the esophagus were well,developed.The submucosa,circular muscle,longitudinal muscle and serosa layers of the small intestine were relatively thinner than those of the rectum.The submucosa and serosa layers of the anterior intestine were relatively thicker than those of the posterior intestine.The density of Paneth cells in the mucosa layer of the small intestine was lower than that of the rectum while the density of goblet cells in the mucosa layer of the small intestine was higher than that of the rectum.The mucosa epithelia of the oral cavity and tongue of this species were stratified squamous epithelia with abundant rounded mucous cells.The taste buds on the tongue and oral cavity were observed.The mucosa layer of the esophagus was well developed.In the proximal esophageal mucosa,a concave-shaped structure was observed in which abundant giant mucous cells distributed.This structure was similar to the exocrine gland,and had an opening at the esophagus.The epithelial cells of the small intestine and rectum were monolayer columnar covered with microvillus; and three kinds of goblet cells were observed.In the submucosa layer,there were many eosinophilic granule cells of which the cytoplasm was stained by eosin.Lipochondria were observed in the monolayer columnar epithelial cells of the anterior intestine.It was also observed that some of the cells were stained by eosin in the epithelium of the rectum.The valves were found between the esophagus and small intestine and between the small intestine and rectum.The muscle layer in the valve consisted of striated muscle.The mucosa layer of the rectum contained a large amount of oval-shaped mucous cells.The digestive gland consisted of hepatopancreas and cholecyst.The liver of the fish had three lobes and was maple leaf-shaped; the pancreas dispersedly distributed in the liver along its blood vessels; gallbladder had an oval shape with a relatively large volume.We also discussed the segments of the intestine,histological features of the alimentary tract of this species,and their relation with the eating habits of the humphead wrasse."