Effects of dietary carbohydrate types on growth performance, innate immunity, antioxidant ability and glucose metabolism of brook troutSalvelinus fontinalis

The study evaluated the effects of different types of dietary carbohydrates on growth, immunity, antioxidant capacity and glucose metabolism enzyme activities in the juvenile brook trout. Fish (13.65 ± 0.06 g) were fed five isonitrogenous and isolipidic diets that contained 150g kg-1 glucose, sucrose, dextrin, pregelatinized corn starch (PS) or raw corn starch (RS) respectively. Weight gain, specific growth rate and protein efficiency ratio were significantly higher in fish fed dextrin than the other treatments. The serum alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (AKP) and glucose were higher in fish fed glucose than those fed dextrin, PS or RS. Hepatic superoxide dismutase (SOD), catalase (CAT) and lysozyme activity, as well as total antioxidant capacity, were lower in fish fed glucose or sucrose than the other treatments. Moreover, the highest malondialdehyde (MDA) level was reported in the glucose group. Furthermore, fish fed glucose had significantly lower hepatic glucokinase (GK), phosphofructokinase (PFK) and phosphoenolpyruvate carboxykinase (PEPCK) activities than those fed dextrin, PS or RS. The results suggest that dextrin is the optimal carbohydrate source for brook trout, while incorporating glucose into the diet suppresses innate immunity, increases oxidative stress and interferes with glucose metabolism, resulting into a reduction in growth.