The mucosal capillaries of the proximal intestine in a freshwater teleost (Prochilodus scrofa) are lined by an endothelial sheet with several fenestrated or pored domes, which are observed both in the thinner and thicker cytoplasmic extensions of the endothelium. These domes sometimes communicate between the inner and the outer side of the capillary wall, forming a transendothelial channel-like structure with internal diaphragms. The pored domes seem to be a frequent structure in fishes. Their ultrastructure in the proximal segment of the intestine, where the flow of substances through the endothelium is intense, is described.