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Sandre LCG, Buzollo H, Neira LM, Nascimento TMT, Jomori RK and Carneiro DJ
The study assessed the protein sparing effect resulting from carbohydrate (CHO) and lipid (LIP) use and metabolic responses of juvenile tambaqui fed diets with different proportions of CHO and LIP. In a completely randomized 3 × 2 factorial design, the 6 diets tested combined 3 CHO (410 gkg-1, 460 gkg-1 and 510 gkg-1) and 2 LIP (40 gkg-1 and 80 gkg-1) levels. The 1080 fish tested (10.88 g ± 0.13 g mean body weight) were randomly distributed into twenty-four 500-L tanks (45 fish per tank). An increase in diet CHO and LIP levels improved feed conversion and protein efficiency ratio. The highest addition of CHO (510 gkg-1) and LIP (80 gkg-1) reduced diet intake and weight gain and increased serum triglyceride levels and fat deposition in muscle and liver. Glucose levels, serum protein and liver glycogen showed no difference between treatments with different CHO and LIP levels. Liver and muscle fat deposition were higher in the treatments with the highest diet LIP level, irrespective of diet CHO. The hepatosomatic index (HSI) and viscerosomatic fat index (VSI) exhibited no differences between treatments. Therefore, tambaqui can use both CHO and LIP to optimize protein use. The physiological responses indicate that the best CHO-LIP combination in tambaqui diets is 460 gkg-1 and 40 gkg-1, respectively. This combination promotes satisfactory growth without causing excess fat accumulation.