Effects Of Replacement Of Dietary Fish Meal By Two New Nongrain Protein Source On Growth Performance,Intestinal Health And Liver Lipid Metabolism In Turbot(Scophthalmus Maximus)

This paper takes turbot(Scophthalmus maximus L),an important marine aquaculture fish,as the experimental object,and conducts an indoor aquaculture experiment on seawater circulation system.The effects of defatted Tenebrio molitor meal and Clostridium ethanolum protein instead of fish meal on growth performance,intestinal health and liver lipid metabolism of turbot were studied.The contents and results of the study are as follows:1.Effects of replacement of dietary fish meal by defatted Tenebrio molitor meal on growth performance,intestinal health and liver lipid metabolism in turbotIn this research,an eight-week feeding trial was conducted to evaluate the effect of defatted Tenebrio molitor meal on turbot mainly from the perspective of growth performance and health status of the intestine and liver.Turbot with an initial weight of approximately 150g were randomly assigned six isonitrogenous and isolipidic diets,including fishmeal-based control diet or diets with gradually increasing level of defatted Tenebrio molitor meal(TM)to replace 15%(TM15),30%,45%,60%and 75%of fishmeal compared to the control diet.Weight gain of turbot increased significantly at the 30%replacement level(P<0.05).However,TM in excess of this amount impaired overall growth performance.There was no obvious impairment in the assayed levels of TM towards the intestine from the view of structure,activities of brush border enzymes,antioxidant conditions,or immunity of proximal,middle and distal segments.However,the amount of goblet cells was significantly decreased by TM(P<0.05).Similarly,TM in the assayed levels did not induce any negative effects on the antioxidant and immune status of the liver.Moreover,dietary TM at 15%and 30%substitution levels improved the antioxidant and immune status of both the intestine and the liver.Diet TM15 also down-regulated most assayed inflammatory-related cytokines.This observation indicates a healthy digestive system,which contributes to the growth-stimulation of TM to an optimal level.However,excess TM-induced weight loss in the liver and smaller hepatocytes was accompanied by a decrease of liver lipid content as well as decreases in levels of triglyceride and cholesterol in plasma.Although turbot up-regulated the expression of key genes for lipid synthesis and exportation in the liver as a means of maintaining lipid levels in the muscles and the body as a whole,the shortage of lipid nutrients was responsible for the growth decline caused by excess TM.In conclusion,the optimal dietary level of TM for turbot was 18.9%,corresponding to a 30%substitution of fishmeal from the control group.Under optimal levels,dietary TM can improve the antioxidant and immune function of the intestine and liver,but excess TM will disturb lipid metabolisms.2.Effects of replacement of dietary fish meal by Clostridium ethanolicum protein on growth performance,intestinal health and liver lipid metabolism in turbotIn this research,an eight-week feeding trial was conducted to evaluate the effect of Clostridium ethanolicum protein on turbot mainly from the perspective of growth performance and health status of the intestine and liver.Turbot with an initial weight of approximately 150g were randomly assigned six isonitrogenous and isolipidic diets,including fishmeal-based control diet or diets with gradually increasing level of Clostridium ethanolicum protein(CAP)to replace 15%(CAP15),30%,45%,60%and 75%of fishmeal compared to the control diet.The weight gain rate of turbot decreased significantly when the replacement ratio reached 45%or above,and the feed intake,feed efficiency and liver efficiency showed a significant linear downward trend(P<0.05).In terms of intestinal tract,CAP supplementation did not cause intestinal inflammatory response of turbot,but resulted in a significant linear decrease in the height of mucosal folds in the distal intestine and middle intestine and the density of mucosal folds in the distal intestine(P<0.05).In terms of liver,with the increase of fish meal replacement level of Clostridium ethoxylum protein,the hepatocyte size and liver fat content of turbot decreased firstly and then increased,while the expression levels of lipid transporter gene and oxidation gene increased firstly and then decreased(P<0.05).Meanwhile,the contents of cholesterol and triglyceride in plasma of turbot decreased linearly with the increase of fish meal replacement level of Clostridium ethanolum protein(P<0.05).In conclusion,the optimal dietary level of CAP for turbot was 15%,corresponding to a 30%substitution of fishmeal from the control group.Excessive CAP will affect the feed utilization capacity of turbot and adversely affect the development of intestinal villus folds.