Effects of dietary carbohydrate levels on growth, metabolic enzyme activities and oxidative status of hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

Abstract

An 8-week feeding trial was aimed to explore the effects of dietary carbohydrate on growth performance, metabolic enzyme activities and oxidative status of hybrid snakehead (Channa maculata ♀ × Channa argus ♂). A total of 540 healthy hybrid snakehead with initial body weight of (39.4 ± 0.01) g were selected and randomly divided into 18 cages, with 30 in each cage. Six isonitrogenous and isolipidic diets with different levels of digestible carbohydrate (α-starch) levels (DCL) (0%, 5%, 10%, 15%, 20% and 25%) were fed to hybrid snakehead. Results showed that dietary carbohydrate supplementation had significant effects on final body weight (FW), weight gain (WG), feed conversion ratio (FCR) and protein efficiency ratio (PER) of hybrid snakehead in a third order polynomial (cubic) model, with the optimal level established at 10.2%–12.0%. Effects on Condition factor (CF) of hybrid snakehead was described by a second order polynomial (quadratic) relationship. Hepatosomatic index (HSI) and viscerosomatic index (VSI) showed a linear relationship with increasing DCL. The body protein, crude lipid and hepatic glycogen content of hybrid snakehead increased with the levels of carbohydrate supplementation (P < 0.05). Dietary supplementation with carbohydrate significantly increased the levels of plasma cholesterol (CHOL), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) in hybrid snakehead (P < 0.05). The activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in both plasma and liver were significantly enhanced by the highest level of carbohydrate (P < 0.05). Furthermore, the levels of superoxide dismutase (SOD) and catalase (CAT) in liver increased firstly and then decreased with the increasing of DCL (P < 0.05). The expression levels of genes encoding SOD, glutathione peroxidase (GSH-PX), proinflammatory cytokines interleukin 1β (IL-1β) and interleukin 8 (IL-8) in liver showed significantly increasing trend when DCL increased from 0% to 15%, followed by significant decline when DCL exceeds 15% (P < 0.05). The malondialdehyde (MDA) contents in liver were not affected by DCL. Based on these results, the optimal level of dietary carbohydrate supplementation was estimated at approximately 11% for maximum growth and normal metabolism of hybrid snakehead.