A histological, histochemical and ultrastructural study of the digestive tract of Dentex dentex (Pisces, Sparidae).

Dentex dentex has a short esophagus, a large caecal type stomach, three to six pyloric caeca and a short intestine. Light and electron microscope studies reveal that the esophageal mucosa displays primary and secondary folds, a stratified squamous epithelium with fingerprint-like microridges alternating with a few zones formed by a single layer of columnar cells with apical microvilli. Only primary folds are present in the stomach, which is rich in simple tubular glands, these being absent in the pyloric valve. Two cell types occur in the gastric glands, one with a well developed apical intracytoplasmic membrane system consisting of a vesicular network of smooth membranes, and the other with a supranuclear tubulovesicular system. Pyloric caeca and anterior and posterior intestine mucosae display the same pattern of folding, with primary and secondary folds, without following a definite pattern in their orientation. In the rectum, the folds are oriented longitudinally. Small dense particles containing chylomicrons appear in groups in the intercellular spaces of the caecal and anterior intestinal epithelia. Eosinophilic granular cells (mast cells) appear along the digestive tract mainly within the stratum compactum. Histochemical studies reveal no differences in the composition of goblet cell mucus along the digestive tract. No histochemical differences were detected between enterocytes of the intestine, pyloric caeca and rectum. Neutral mucosubstances dominate in the stomach epithelium and in the goblet cells of the esophagus, pyloric caeca and anterior intestine. Results of the present study are discussed in relation to descriptions of the digestive tract in other sparids.