The presence of the nematode Spinitectus jamundensis in cardial and pyloric regions of the stomach of Prochilodus lineatus is observed. Samples of the parasitated stomach were analyzed by histological techniques using Hematoxilin-Eosin and Mallory (Azan) Heidenhain's stainnigs. The macroscopical description of the inner surface of the stomach showing damages in the parasites penetration sites, were observed. Histological observations show that the parasite enters the mucous membrane reaching muscular mucous membrane of the cardial region or the epithelial plaits in the pyloric region reaching up to the muscular layer without crossing it. In this way, the parasite reamins confined by a thin layer of connective tissue and in almost direct contact with tissue liquids. Sometimes, in host tissues as responde to the parasite presence, an increased level in the amount of lymphocytes in the surrounding tissues is observed.