Carbohydrate handling in frugivorous tambaqui (Colossoma macropomum): enzymatic and glycemic responses to dietary sugars

Tambaqui (Colossoma macropomum) is a fruit and seed-consuming omnivorous frugivorous fish. It has the metabolic capacity to process dietary carbohydrates, representing an interesting biological model for metabolic studies. We aimed to evaluate the glycaemic response and intermediate metabolism of tambaqui after administering different carbohydrates. A total of 300 juvenile tambaqui with an average weight of 111.5 ± 49.8 g were used. The fish were orally administered 200 mg/100 g body weight of glucose, fructose, sucrose, starch, or saline solution (control). Blood and liver samples were collected at 0 h (baseline) and 3, 6, 9, and 12 h after administration. Plasma glucose concentration, blood metabolites, and the hepatic activity of key metabolic enzymes were analysed. Elevated plasma glucose concentrations were observed 3 h after glucose, fructose, and sucrose administration and 6 h after starch administration. After 9 h, blood glucose levels in all groups returned to baseline. Increased hepatic activity of pyruvate kinase and glucokinase was observed 9 h after the administration of all the tested sugars. This was associated with a decrease in the activity of the gluconeogenic enzyme fructose-1,6-bisphosphatase. Fish fed starch and glucose exhibited increased hepatic fatty acid synthase activity at 6 and 9 h, respectively. Tambaquis have a high capacity to use all the tested sugars for energy purposes. However, fructose and sucrose did not stimulate metabolic synthesis of lipids because of excess sugar intake.