Morphology of the air‐breathing stomach of the catfish Hypostomus plecostomus

Abstract

Histological and ultrastructural investigations of the stomach of the catfish Hypostomus plecostomus show that its structure is different from that typical of the stomachs of other teleostean fishes: the wall is thin and transparent, while the mucosal layer is smooth and devoid of folds. The epithelium lining the whole internal surface of the stomach consists of several types of cells, the most prominent being flattened respiratory epithelial cells. There are also two types of gastric gland cells, three types of endocrine cells (EC), and basal cells. The epithelial layer is underlain by capillaries of a diameter ranging from 6.1-13.1 microm. Capillaries are more numerous in the anterior part of the stomach, where the mean number of capillary sections per 100 microm of epithelium length is 4, compared with 3 in the posterior part. The cytoplasm of the epithelial cells, apart from its typical organelles, contains electron-dense and lamellar bodies at different stages of maturation, which form the sites of accumulation of surfactant. Small, electron-dense vesicles containing acidic mucopolysaccharides are found in the apical parts of some respiratory epithelial cells. Numerous gastric glands (2 glands per 100 microm of epithelium length), composed of two types of pyramidal cells, extend from the surface epithelium into the subjacent lamina propria. The gland outlets, as well as the apical cytoplasm of the cells are Alcian blue-positive, indicating the presence of acidic mucopolysaccharides. Zymogen granules have not been found, but the apical parts of cells contain vesicles of variable electron density. The cytoplasm of the gastric gland cells also contains numerous electron-dense and lamellar bodies. Gastric gland cells with electron-dense cytoplasm and tubulovesicular system are probably involved in the production of hydrochloric acid. Fixation with tannic acid as well as with ruthenium red revealed a thin layer of phospholipids and glycosaminoglycans covering the entire inner surface of the stomach. In regions of the epithelium where the capillaries are covered by the thin cytoplasmic sheets of the respiratory epithelial cells, a thin air-blood barrier (0.25-2.02 microm) is formed, thus enabling gaseous exchange. Relatively numerous pores closed by diaphragms are seen in the endothelium lining the apical and lateral parts of the capillaries. Between gastric gland cells, solitary, noninnervated endocrine cells (EC) of three types were found. EC are characterized by lighter cytoplasm than the surrounding cells and they contain dense core vesicles (DCV) with a halo between the electron-dense core and the limiting membrane. EC of type I are the most abundant. They are of an open type, reaching the stomach lumen. The round DCV of this type, with a diameter from 92-194 nm, have a centrally located core surrounded by a narrow halo. EC of type II are rarely observed and are of a closed type. They possess two kinds of DCV with a very narrow halo. The majority of them are round, with a diameter ranging from 88-177 nm, whil...

Morphology of the pharyngeal cavity, especially the surface ultrastructure of gill arches and gill rakers in relation to the feeding ecology of the catfish Rita rita (Siluriformes, Bagridae)

“…The role of mucous secretions in the lubrication of food during its passage in the gut in different fish species is widely accepted (Ezeasor and Stokoe, 1980;Martin and Blaber, 1984;Chakrabarti, 1985, 1986;Anderson, 1986;Chakrabarti and Sinha, 1987;Park and Kim, 2001;Podkowa and Goniakowska-Witalinska, 2003). Mucus in different fish species has also been considered to play an important role in various food-processing activities.…”

Influence of season, environment and feeding habits on the enzymatic activity of peptidase and β-glucosidase in the gastrointestinal tract of two Siluriformes fishes (Teleostei)

“…It is important to point out that the enzymatic activity assayed in this study can be both from the gastrointestinal lumen and from the extracts of epithelial cells. The peptidase activity with chymotrypsin-like and trypsin-like specificities observed at pH 8 in the stomach probably came from the epithelial cells, since these fish species have stomachs with acid digestion in the lumen (PODKOWA & GONIAKOWSKA-WITALIÑSKA 2003, SANTOS et al 2007). Nevertheless, the overall enzymatic activity was useful to distinguish two Siluriform species with different feeding habits.…”

Functional facets of the pulmonary neuroendocrine system

“…34 In addition to appearing early in the developing mammalian lung, PNECs are present in lower vertebrates, suggesting that they are phylogenetically an integral early part of the pulmonary development [35][36][37][38] (Figure 1). During the history of vertebrates, the PNEC system in the air-breathing organs has developed in several evolutionary lineages, which are phylogenetically independent from each other.…”