Proper inclusion of carbohydrates in aquafeeds can increase protein and lipid retention preventing the catabolism of these nutrients for energy purposes. This research aimed to evaluate performance, metabolic and enzymatic indicators in pacu (Piaractus mesopotamicus) juveniles fed diets with 350 or 400 g/kg starch (S) and 190 or 210 g/kg digestible protein (P) (diets S35P19, S35P21, S40P19 and S40P21 respectively). Overall, the best growth performance was achieved with diet S35P21. Dietary protein and starch levels had no effect on feed intake, feed conversion ratio and protein efficiency ratio. The lowest whole‐body protein content was recorded in fish fed the S35P19 diet, while fish fed diet S40P21 presented the highest whole‐body lipid content. Regardless of dietary protein level, S40 diets led to higher plasma glucose and triglycerides levels, and higher liver glycogen content. No differences were observed on hepatosomatic index or muscle lipids content. Increasing dietary starch level led to an increase in mesenteric fat index and in liver glucokinase activity, while higher dietary protein promoted a decrease in liver lipid content. Fish fed diet S40P21 showed higher liver glucose‐6‐phosphate dehydrogenase activity than fish fed the S35P21 and S40P19 diets. Dietary protein and starch levels had no effect on pyruvate kinase and fructose‐1,6‐bisphosphatase activity. Overall, dietary starch enhanced glycolytic and lipogenic pathways but did not depress gluconeogenic pathway. The results of this study indicate that a diet with 350 g/kg starch and 210 g/kg digestible protein was the most adequate for pacu in terms of growth performance and feed utilization.

The aim of this study was to assess the activity of gastric, pancreatic and intestinal digestive enzymes during the embryonic and larval development of Nile tilapia (Oreochromis niloticus) GIFT strain Aqua America® 1 obtained from a broodstock fed two levels of crude protein (CP). A total of 72 females and 24 males, 10 hapas, two CP levels (32% and 38%) and six phases of embryonic (cleavage, blastula, gastrula) and larval (hatching, 7 and 10 days post hatch, dph) stages were used. The eggs were collected in cleavage, blastula and gastrula stages, 300 mg was collected, and kept in cryogenic tubes in liquid nitrogen. For the samples at larval stage, the remaining eggs were separated according to crude protein level and kept in hatcheries and samples were collected on 7 and 10 dph the same way as before. A total of 48 samples were collected: at each protein level (32% and 38% CP), four samples were collected in each phase of embryonic and larval development. Statistical differences were not observed during embryonic development for acid proteases, trypsin, amylase and lipase activity at both levels of crude protein (32 and 38% CP). Differences for acid proteases were noticed on 7 dph; trypsin and amylase on 7 dph and 10 dph. Significant differences on blastula and 7 dph for protease; as for aminopeptidase, there was significant difference on 7 dph. The data indicated early appearance of digestive enzymes in Nile tilapia broodfish receiving 32% CP taking into account the rapid growth and development of this species.

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