Effects of dietary glutamine on survival, growth performance, activities of digestive enzyme, antioxidant status and hypoxia stress resistance of half-smooth tongue sole (Cynoglossus semilaevis Günther) post larvae.

A 30-day feeding trial was conducted to evaluate the effects of dietary glutamine supplementation on survival, growth performance, activities of digestive enzyme, antioxidant abilities and hypoxia stress tolerance of larval half-smooth tongue sole, Cynoglossus semilaevis (35 days after hatching, 10.64 ± 0.86 mg). Four isonitrogenous and isolipidic experimental diets were formulated with supplementation of graded levels (0.0, 0.5, 1.0 and 2.0% dry diet) of glutamine (with free dietary glutamine estimated to be about 0.03, 0.46, 0.91, 1.73% dry diet), and were randomly assigned to triplicate groups of post larvae (150 post larvae per tank) to apparent satiation five times daily. The results indicated that, survival and growth performance of fish fed all glutamine-supplemented diets were significantly increased compared to the control group (P < 0.05). Fish fed the diet supplemented with 0.5% or 1.0% glutamine showed significantly higher activities of trypsin in intestinal segments compare to those fed 0.0% or 2.0% glutamine diet (P < 0.05). Meanwhile, fish fed the diet with 2.0% glutamine had significantly higher activities of amylase in both intestinal segments and pancreatic segments than those fed the control diet (P < 0.05). Specific activities of alkaline phosphatase (AKP) and leucine-aminopeptidase (LAP) in brush border membranes (BBM) were significantly higher in fish fed all glutamine-supplemented diets compared to the control (P < 0.05). Fish fed the 2.0% glutamine diet showed significantly lower malondialdehyde (MDA) contents in larval whole body than those in the control group (P < 0.05). Activities of glutathione peroxidase (GPX) were significantly higher in fish fed the diet with 0.5% glutamine compared with those in fish fed the 2.0% glutamine diet (P < 0.05). No significant difference was found in activities of superoxide dismutase (SOD) and catalase (CAT) among dietary treatments (P > 0.05). Fish fed diets supplemented with 0.5–2.0% glutamine showed significantly higher GPX expression and lower CAT expression than those in fish fed the control diet (P < 0.05). Compared with the control group, median lethal dissolved oxygen levels were significantly lower in fish fed 0.5% and 1.0% glutamine diets while HSP70 expression were significantly stimulated after hypoxia stress in fish fed diets supplemented with 0.5% and 2.0% glutamine (P < 0.05). In conclusion, dietary glutamine supplementation could promote survival and growth of C. semilaevis post larvae through improving activities of digestive enzyme, enhancing antioxidant abilities and hypoxia stress resistance. The optimal dietary free glutamine level based on SGR for C. semilaevis post larvae in the present study was estimated to be approximately 0.63% dry diet. Statement of relevance The present study mainly investigated effects of dietary glutamine on growth performance, antioxidant ability and stress resistance of half-smooth tongue sole ( Cynoglossus semilaevis ) post larvae. Our findings have showed that dietary glutamine could improve growth performance of C.semilaevis post larvae, and for the first time revealed that dietary glutamine could modulate gene expression of antioxidant enzymes in C. semilaevis post larvae. The results are reliable and of both theoretical and practical importance. The work described has not been submitted elsewhere for publication, in whole or in part, and all the authors listed have approved the manuscript that is enclosed.I have read and have abided by the statement of ethical standards for manuscripts submitted to Aquaculture. [ABSTRACT FROM AUTHOR]