Morphological analysis of the digestive tract of Hypophthalmus marginatus (Valenciennes, 1840).

The mapará, Hypophthalmus marginatus, is a rheophilic and planktophagous catfish and it is one of the main fishing resources in the Amazon region. To understand its nutritional characteristics, this work described the morphology and histochemistry of the digestive tract of H. marginatus. The oropharyngeal cavity has abundant, long and thin gill rakers, responsible for retaining plankton, while the short and muscular oesophagus promotes the transport of these items to the stomach and prevents water ingestion. The stratified oesophageal epithelium has goblet cells with mucins predominantly neutral that could facilitate the food passage the food passage. The U-shaped siphonal stomach shows a columnar epithelium with neutral mucins to protect against autodigestion. The cardiac and fundic regions have gastric glands, while the pyloric region has a thick muscular layer with a sphincter. The coiled intestine with intestinal quotient of 2.14 ± 0.5 shows long longitudinal folds in the anterior region, decreasing in height in the aboral direction, and highlighting its function in digestion and nutrient absorption. Goblet cells are abundant in posterior intestine and rectum, and rectum shows epithelial cells with mucins in the apical cytoplasm, for protection and defecation. Intraepithelial lymphocytes also are abundant in posterior intestine and rectum, and it acts in immunological defence.