Carbohydrate utilization in black seabream: Effects of the carbohydrate sources on growth, insulin signalling pathway and hepatic glucose metabolism

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate sources on growth, insulin signalling pathway and hepatic glucose metabolism in juvenile black seabream (Acanthopagrus schlegelii). Five isonitrogenous (480 g/kg) and isolipidic (120 g/kg) experimental diets were formulated to contain 200 g/kg glucose (GLU), sucrose (SUC), wheat starch (WS), corn starch (CS) and dextrin (DEX), respectively. The results indicated that fish fed the WS, CS and DEX diets exhibited the higher per cent weight gain and protein efficiency ratio than those fed the GLU and SUC diets (p < .05). Fish fed the GLU diet had the lowest survival and condition factor among all treatments (p < .05). Maillard reaction had occurred in the glucose diet due to moist heat process, drying and storage of the glucose diets suggested a lower lysine level in this diet than the other diets. The expression of irs1 and pi3k was significantly up-regulated in fish fed the DEX diet (p < .05). Moreover, the relative mRNA expression of genes involved in glycolysis such as hk and pk was down-regulated in fish fed the GLU and SUC diets (p < .05). The expression of genes related to gluconeogenesis such as pepck and fbp was not significantly influenced by dietary carbohydrate sources (p > .05). However, fish fed the WS, CS and DEX diets has higher expression of g6pc than those fed the other diets (p < .05). The results of present study demonstrated that fish fed the polysaccharide diets (WS, CS and DEX) had better growth than those fed the monosaccharide (GLU) or disaccharide (SUC) diets. However, severe Maillard reaction in the glucose diets resulted in significant reduction in the growth performance of the fish. The mRNA expressions of hepatic genes involved in glycolysis, gluconeogenesis and insulin signalling pathway were significantly affected by dietary carbohydrate sources.