A comparative histological and histochemical study of the stomach from three species of pleuronectid, the Atlantic halibut, <i>Hippoglossus hippoglossus</i>, the yellowtail flounder, <i>Pleuronectes ferruginea</i>, and the winter flounder, <i>Pleuronectes americanus</i>

Abstract

The morphology and the histochemistry of the mucus of the pleuronectid stomach were examined using light and electron microscopy. The stomach of the winter flounder (Pleuronectes americanus) and the yellowtail flounder (Pleuronectes ferruginea) possessed a glandular or cardiac region and an aglandular or pyloric region, whereas the stomach of the Atlantic halibut (Hippoglossus hippoglossus) was entirely glandular in nature. The epithelia of the glandular region in all three species could be divided into three distinct zones based upon ultrastructural differences in the cell types present. Zone 1 contained surface mucus-secreting cells, zone 2 contained mucous neck cells, and zone 3 contained oxyntico-peptic cells or gland cells. The presence of ultrastructurally distinct cells in the neck region is not consistent with observations of all teleost species and supports the theory that teleost gastric glands may exist with or without distinct mucous neck cells. Variation in mucous histochemistry across gastric zones as well as between species suggests that the chemical nature of the luminal environment during digestion may be different as a consequence of differences in natural diet. Two types of enteroendocrine-like cells were identified in association with zone 1, based upon granule morphology: type I was of the "closed" variety, but the variety of the type II enteroendocrine-like cell was not resolved from this study.