Carbohydrate tolerance in the fruit-eating fish Piaractus mesopotamicus (Holmberg, 1887)

Some fish species have a limited ability to metabolize dietary carbohydrates. An important tool for understanding carbohydrate metabolism is the application of the glucose tolerance test, which can be performed orally or intraperitoneally. To evaluate carbohydrate tolerance in the fruit-eating fish pacu, two experiments were performed, one with oral administration by gavage of three carbohydrate types (glucose, fructose and starch, 2.0g/kg body weight (BW)) and the other with intraperitoneal injection (IP) of glucose (500mg/kg BW). Oral glucose resulted in an increase in plasma glucose 2hr later with the peak at 4hr (8.30mmol/L), and return to baseline between 6 and 12hr; starch administration promoted a peak after 4hr (7.70mmol/L), returning to the baseline at 6hr. The administration of fructose promoted a moderate peak after 2hr (5.71mmol/L), and return to baseline for the time points that followed. Elevated serum cholesterol levels were observed 2 and 24hr after administration of glucose and starch. Hepatic glycogen levels increased within 24hr, regardless of the type of carbohydrate administered. IP glucose load resulted in a peak of plasma glucose 3hr post injection (6.91mmol/L), returning to baseline 6hr later. There was a reduction in the concentration of triglycerides at 24hr. The results demonstrate that pacu metabolize both oral (glucose or starch) and intraperitoneal (glucose) carbohydrate loads after 6hr, suggesting good ability to deal with dietary carbohydrates.