A morphological, glycohistochemical and ultrastructural study on the stomach of adult Rainbow trout Oncorhynchus mykiss

In this study the morphology, the conventional glycohistochemistry and the ultrastructure of adult rainbow trout (Oncorhynchus mykiss) stomach is reported. For this purpose, stomach belonging to 10 adult female rainbow trout, weighting ~ 500 ± 20 gr and 32 ± 2.50 cm long, were collected and processed. Oncorhynchus mykiss has a siphonal stomach, with a J letter shape, showing a descending portion (cardiac region), an ascendant one (pyloric region), connected through the most represented middle portion (fundic region). Morphologically gastric wall shows an overlay of four typical vertebrate tunicae: mucosa, sub-mucosa, muscularis and serosa. Tunica mucosa, lacking of muscularis mucosae, is raised into longitudinal folds. The tunica propria submucosa is of considerable thickness and receives the bodies of many gastric glands whose lumen is lined with oxyntopeptic cells. Nervous cells, organized in ganglion, that can be compared to Mammals plexus submucosus, are noted. Glycohistochemistry was performed by staining with Periodic acid–Schiff (PAS), Alcian blue (AB) pH 2.5, AB pH 1 and AB-PAS. Histochemical analysis revealed a consistent presence of glycoconjugates produced by epithelial lining and gastric pit cells. Ultrastructural studies, performed at scanning electron microscopy, showed a mucosa that rises in folds with a geometrically well-defined shape and an abundance of gastric pits in the fundic region. Taken together our results integrate the anatomical description of rainbow trout stomach and will be helpful for future studies related to digestive physiology, development of appropriate feeding strategies and gastric disease control of this teleostean species