Dietary protein/carbohydrate ratio and feeding frequency affect feed utilization, intermediary metabolism, and economic efficiency of gilthead seabream (Sparus aurata) juveniles

To evaluate the effects of dietary protein/carbohydrate (P/CHO) ratio and feeding frequency (FF) on growth, intermediary metabolism, and economic efficiency of gilthead seabream (Sparus aurata) juveniles, two practical isolipidic (17%) diets were formulated to include high protein (50%)/ low starch (10%) (diet P50/CHO10) or low protein (40%)/ high starch (20%) (diet P40/CHO20). Triplicate groups of fish with 9.1 & PLUSMN; 0.01 g were fed for 60 days with these diets until visual satiation at three FF: one (9:00), two (9:00 and 17:00), or three (9:00, 13:00, and 17:00) meals per day. Dietary P/CHO ratios did not affect growth performance while feeding 2 or 3 meals per day improved fish growth. Fish fed diet P40/CHO20 had increased feed intake (FI), protein efficiency ratio (PER), and nitrogen retention (NR), and lower feed efficiency (FE), nitrogen intake (NI), and economic conversion ratio (ECR). Feeding 2 or 3 meals per day increased FI, NI, ECR, and economic profit index, and decreased FE, PER, and NR. Fish fed diet P40/CHO20 presented increased hepatic lipid and glycogen content, hepatocyte area covered by lipid vacuoles, and glucokinase (gk) gene expression, and decreased glutamate dehydrogenase expression. Fish fed 3 meals per day had decreased plasma triglycerides and total protein levels, while fish fed 2 or 3 meals per day presented decreased hepatic growth hormone receptor-i (ghr-i), gk, and fatty acid synthase gene expression. Interaction between P/CHO ratio and FF was only observed in plasmatic glucose, cholesterol, and total lipids levels, and insulin-like growth factor-1, and ghr-ii gene expression. Overall, glycogenesis, glycolysis, and economic efficiency seemed to be increased while the amino acid catabolism was reduced in fish fed the P40/CHO20 diet. Higher FF increased growth and economic efficiency, and reduced glycolysis and lipogenesis pathways. In conclusion, a diet with P40/CHO20 ratio fed twice a day appears to be the most adequate strategy regarding feed utilization and economic efficiency for gilthead seabream juveniles in order to achieve optimum sustainable aquaculture.