High protein-low carbohydrate diet can improve hypoxia tolerance of triploid rainbow trout (Oncorhynchus mykiss): Effects on physiological and metabolic responses to acute hypoxia

Abstract

Triploid rainbow trout is a hypoxia-sensitive fish species, and is susceptible to death in summer with high water temperature induced acute hypoxia. The study was conducted to evaluate the effect of high protein diet and high carbohydrate diet on hypoxic tolerance of triploid rainbow trout. Two isolipidic and isoenergetic diets with low protein-high carbohydrate level (LPHC) and high protein-low carbohydrate level (HPLC) were specifically formulated. After the feeding trial with 80 days, two group fish were treated with acute hypoxic challenge. Plasma biochemical parameters, hepatic anti-stress, antioxidant and immune related genes expression, and hepatic glucose, lipid, protein and amino acid metabolism related genes expression were then analyzed. The results showed that compared with HPLC diet, LPHC diet could result in excessive plasma levels of alanine aminotransferase (ALT; 36.3 VS 14.0 U/L), aspartate aminotransferase (AST; 978 VS 366 U/L), alkaline phosphatase (ALP; 374 VS 204 U/L), creatine phosphokinase (CPK; 7538 VS 4937 U/L) and lactate dehydrogenase (LDH; 940 VS 451 U/L). In addition, HPLC diet could remodel metabolism of glucose, lipid and protein based on the mRNA expression levels of the genes regulating glycometabolism, lipometabolism, and protein and amino acids metabolism. HPLC diet also enhanced the mRNA expression levels of the genes regulating anti-stress (HSP70, HIF-1a and HIF-2a), antioxidant (Nrf2, SOD, CAT, GPx and HO-1) and immune (IFN-γ, IL-1β, TNF-α and IL-8). In total, LPHC diet could aggravate hypoxic stress of triploid rainbow trout, while HPLC diet could improve fish hypoxic tolerance.