Digestive physiology of the Amazonian freshwater stingray, Potamotrygon wallacei (Elasmobranchii: Potamotrygonidae): processing capacity for proteins, lipids and carbohydrates

Abstract In this study, we used digestive enzyme profiles to understand the proteolytic, lipolytic potential and capacity to hydrolyze carbohydrates in the digestive tube of the Amazonian freshwater stingray, Potamotrygon wallacei. The processing capacity for proteins, lipids and carbohydrates was examined using the absolute activities of digestive enzymes. The results of this study showed that the stingray P. wallacei has a high activity of acid proteases such as endoproteases (pepsin and elastase) in the stomach and high proteolytic potential (trypsin, chymotrypsin, elastase and leucine amino peptidase) in the spiral intestine. This can be explained by the fact that P. wallacei has a protein-rich diet, preferably based on crab, shrimp, insect larvae and small fish in their natural environment. The activities of non-specific lipases and esterases (both in the cardiac stomach and spiral intestine) suggest a high capacity for lipolysis, possibly to hydrolyze high lipid contents present in insect larvae. Although carbohydrates are not macronutrients that are found in significant levels in the food items of this stingray, in our study, it was observed that the carbohydrates were also upregulated. The SEM-based model suggests the usual pattern showing the common role of endopeptidases (chymotrypsin and elastase) associated with leucine amino peptidase and trypsin in the other parallel pathway to complete the digestion of proteins in the spiral intestine. P. wallacei appears to have no detectable amount of carboxypeptidase A, which is possibly due to the strong action of stomach pepsin. The results of this study may help in the management of this species in captivity, especially related to feeding habits.