Effect of high level of carbohydrate and supplementation of condensed tannins on growth performance, serum metabolites, antioxidant and immune response, and hepatic glycometabolism gene expression of Lateolabrax japonicus

Condensed tannins (CT) have been observed to be beneficial to maintain glucose homeostasis and improve carbohydrate utilization for livestock, whereas little information is available about the effects of CT on glycometabolism of fish. Three diets were formulated to contain approximately 15 % carbohydrate (G1), 39 % carbohydrate (G2), and G2 supplemented with 0.1 % CT. A total of 225 juvenile Lateolabrax japonicus were randomly assigned to 3 groups (triplicate tanks per group) with 25 fish in each tank and fed to apparent satiation during 56-d feeding trial. Results indicated that fish fed G2 had lower (p < 0.05) final body weight, weight gain rate, feed intake, specific growth rate and serum insulin concentration, but higher (p < 0.05) feed efficiency ratio and serum glucose, total antioxidant capacity, superoxide dismutase, immunoglobulin M and lipopolysaccharide than those fish fed G1 or G3. The activity of pyruvate kinase (PK) was lower (p < 0.05) but glucokinase (GK) was higher (p < 0.05) in G2 than in G1 or G3. Gene expression of insulin like growth factor Ⅰ and PK were down-regulated (p < 0.05), whereas GK was up-regulated (p < 0.05) in G2 than in G1 or G3. No difference (p> 0.05) in these gene expressions were observed between G1 and G3. It was concluded that L. japonicus fed diet with 39 % carbohydrate exhibited depressed growth performance, increased antioxidant and immune capacity, and hyperglycemia. Supplementation of 0.1 % CT resulted in improved growth performance and decreased serum glucose concentration, mainly due to the positive effects of CT on the activity and gene expression of hepatic glycolysis and gluconeogenesis enzymes of L. japonicus.