On the structure of intestine and presence of endocytic cells in the lamina propria of platy and black tetra (Teleostei)

The structure of the intestine in platy (Xiphophorus maculatus) and black tetra (Gymnocorymbus ternetzi) and the capability of cells within the intestinal wall to endocytose intraperitoneally injected horse-spleen ferritin, are described. The intestinal epithelial layer has about the same thickness in both species, but the width of the lamina propria and tunica muscularis in black tetra was only about 1/5 of that in platy. Ferritin was taken up by numerous cells within the lamina propria throughout the entire length of the platy intestine. The uptake was demonstrated as large and strongly coloured intracellular Prussian blue granules in sections treated with acid ferrocyanide. There was no such uptake by the lamina propria in black tetras. We suggest that the high numbers of endocytic cells within the intestinal lamina propria of platies provide a local defence against foreign cells and particles. Such a functional role may to some extent compensate for the lack of an HCl-based defence in the digestive system of this stomach-less species.