Anatomy of the alimentary tract of Salminus brasiliensis (Cuvier, 1817) (Pisces, Characidae, Salmininae)

The alimentary tract of Salminus brasiliensis shows anatomic adaptations to its carnivorous, ichthyophagous feeding habit, particularly regarding the distensible esophagus and stomach, especially the caecal region, and the relatively short intestine. The great distensibility of the wall of the anterior intestine is due mainly to the pattern of the mucous membrane, which exhibits thick longitudinal folds. In the anterior intestine the transport of the food is facilitated by the longitudinal pattern of the mucous folds. In the esophagus and pyloric region, related to the propulsion of food to the net organ, the muscular tunica is more developed than in the rest of the alimentary tract. The pyloric constriction regulates the food flux to the middle intestine. Due to the pattern of mucous membrane of the middle and posterior intestines, in net form, the material being processed can be retained for a greater length of time. The intestinal effective absorption area is amplified due to the tubular structure of the middle intestine, of the mucous intestinal folds, and the pyloric caeca. The alimentary tract of S. brasiliensis is similar in structure to that of other Salmininae and to the majority of the piscivorous Characiformes such as Acestrorhynchus britskii and A. lacustris, although in these two the ileum-rectal valve is found. It also differs from the alimentary tracts of Hoplias malabarius and H. lacerdae, in that the esophagus has variable caliber, the stomach possesses a wider cardia, and the intestinal arrangement is different from “N”, besides the presence of the ileum-rectal valve.