Research On Optimal Digestible Carbohydrate Requirement And Plant Extracts On Growth,Metabolism,Antioxidant And Anti-inflammatory Capacity Of Hybrid Snakehead (Channa Maculata♀×Channa Argus♂)

The hybrid snakehead is a carnivorous fish derived from a cross-breeding between male Channa argus and female Channa maculata.It is an economically valuable freshwater fish wildly cultured in south China,due to its rapid growth,hypoxia tolerance,and availability of artificial feeds and large market demand.As such,the hybrid snakehead culture is continuously expanding.To date,the dietary carbohydrate requirements of hybrid snakehead have not been studied,and only few studies on Channa argus have been published.Researches on optimal digestible carbohydrate level and metabolic regulation under high carbohydrate level have not been reported.In this study,the optimal digestible carbohydrate levels and the effects of different carbohydrate levels with plant extracts feed additives supplementation on growth,metabolism and Antioxidant Capacity of hybrid snakehead are investigated,which provides greater understanding of the physiology of hybrid snakehead and allows more refined formulation of feeds for this fish.This study mainly consisted of two feeding experiments with the same feeding conditions.In feeding experiment 1,a total of 540 healthy hybrid snakeheads with initial body weight of(39.4±0.01)g were selected and randomly divided into 18 cages,with 30 fish in each cage.To study the dietary utilization effects of different levels of digestible carbohydrate(α-starch)in six isonitrogenous diets(0%,5%,10%,15%,20% and 25%).In the second feeding experiment,to evaluate the effects of plant extracts feed additives on metabolic enzyme activities and oxidative status of hybrid snakehead with different carbohydrate levels,0.00% and 0.15% of plant extracts feed additives were added to 10% and 20% carbohydrate level diets,respectively.1.In addition,orthogonal polynomial contrasts(linear,quadratic and cubic)were used to evaluate the responses of growth performance to dependent variables.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),interleukin 8(IL-8),interleukin 12(IL-12),Tumor Necrosis Factor-α(TNF-α)and TOR in liver showed significantly increasing trend when DCL increased from 0% to 15%,followed by significant decline when DCL exceeds 15%(P <0.05).Interleukin-10(IL-10)and inhibitor of NF-κBα(IκBα)showed the opposite trend.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.2.The growth performance of hybrid snakehead in 20% carbohydrate group was extremely lower than that in 10% group(P<0.01),plasma alanine aminotransferase(ALT)activity was significantly decreased(P<0.05),liver malondialdehyde(MDA)content was extremely decreased(P<0.01),liver AST activity was extremely decreased(P<0.01),liver SOD and CAT activities were extremely increased(P<0.01),and liver IL-10,IκBα,IL-1β,IL-8,TNF-α and TOR gene expressions were extremely up-regulated(P<0.01)by adding 0.15% plant extracts feed additives.In conclusion,the addition of plant extracts feed additives could improve the growth performance of hybrid snakehead under suitable carbohydrate condition,and relieve the oxidative stress caused by high carbohydrate stress.