饲料胆固醇含量对斜带石斑鱼生长性能、组织生化指标和肝脏脂肪代谢相关酶活性的影响

本试验旨在研究饲料胆固醇含量对斜带石斑鱼生长性能、组织生化指标和肝脏脂肪代谢相关酶活性的影响。在以酪蛋白为主要蛋白质源的基础饲料中分别添加0(对照组)、5、10、15、20和25 g/kg的胆固醇,配制成6种等氮等能试验饲料,并分别命名为C0、C0.5、C1、C1.5、C2和C2.5,饲料中胆固醇实测含量分别为2.6、7.5、12.7、17.2、22.2和27.2 g/kg,投喂360尾平均初重为(84.30±0.25)g的斜带石斑鱼10周。每种试验饲料设3个重复,每个重复投喂20尾鱼。结果表明:随着饲料胆固醇含量的升高,增重率(WGR)、蛋白质效率(PER)和饲料效率(FE)呈先上升后下降的趋势。C0.5组WGR、PER和FE最高且显著高于对照组(P0.05)。各添加组全鱼粗脂肪含量显著高于对照组(P0.05),粗灰分含量显著低于对照组(P0.05)。肝脏总胆固醇(TC)和甘油三酯(TG)含量随饲料胆固醇含量的升高而上升,肌肉TC和TG含量不受饲料胆固醇含量的显著影响(P0.05)。随饲料胆固醇含量的上升,血清TC、TG、高密度脂蛋白胆固醇(HDL-C)和低密度脂蛋白胆固醇(LDL-C)含量先上升后趋于平稳,血清HDL-C/LDL-C呈下降趋势。C2.0组血清TG含量显著高于对照组(P0.05),C2.5组血清HDL-C含量显著高于对照组和C0.5、C1.5组(P0.05),C2.5组血清LDL-C含量显著高于其他各组(P0.05),对照组血清HDL-C/LDL-C显著高于各添加组(P0.05)。随着饲料胆固醇含量的升高,斜带石斑鱼肝脏苹果酸酶(ME)活性呈升高趋势,C1.5、C2.0和C2.5组显著高于其他组(P0.05);肝脏肉毒碱棕榈酰转移酶Ⅰ(CPTⅠ)活性先下降后趋于平稳,对照组显著高于其他组(P0.05);肝脏CYP7A1活性则先上升后趋于平稳,以C2.5组活性最高,较对照组升幅达35.48%(P0.05)。本试验中,以W GR和肝脏胆固醇7α-羟化酶(CYP7A1)活性为评价指标进行折线模型分析得出,斜带石斑鱼对饲料中胆固醇的需要量分别为7.43和8.70 g/kg。

Effects of Dietary Cholesterol Content on Growth Performance,Tissue Biochemical Indices and Liver Lipid Metabolism Related Enzyme Activities of Orange-Spotted Grouper(Epinephelus coioides)

A feeding trial was conducted to evaluate the effects of dietary cholesterol content on growth performance,tissue biochemical indices and liver lipid metabolism related enzyme activities of orange-spotted grouper (Epinephelus coioides).Taking casein as main protein source,six isoenergetic and isonitrogenous diets were formulated with the cholesterol adding levels of 0 (control group),5,10,15,20 and 25 g/kg,named as C0,C0.5,C1,C1.5,C2 and C2.5,and the measured values of cholesterol content in those diets were 2.6,7.5,12.7,17.2,22.2 and 27.2 g/kg,respectively,and then fed to 360 orange-spotted grouper with initial average body weight of (84.30±0.25) g for 10 weeks.Each diet was randomly assigned to three replicates with 20 fishes in each replicate.The results showed as follows:weight gain rate (WGR),protein efficiency ratio (PER) and feed efficiency (FE) were firstly increased and then decreased with the dietary cholesterol content increasing.The WGR,PER and FE of the C0.5 group were the highest and significantly higher than those of the control group (P＜0.05).The whole body crude lipid content of adding groups was significantly higher than that of the control group (P＜0.05),whereas the ash content of supplementation groups was significantly lower than that of the control group (P＜0.05).The total cholesterol (TC) and triglyceride (TG) contents in liver were increased with the dietary cholesterol content increasing,but the muscle TC and TG contents were not affected by dietary cholesterol content (P＞0.05).With dietary cholesterol content increasing,serum TC,TG,high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) contents were firstly increased and changed to be steady,and the HDL-C/LDL-C had a down trend.The serum TG content of the C2.0 group was significantly higher than that of the control group (P ＜ 0.05),the serum HDL-C content of the C2.5 group was significantly higher than that of the C0.5 and C1.5 groups,control group (P＜0.05),the serum LDL-C content of the C2.5 group was significantly higher than that of the other groups (P＜0.05),and the HDL-C/LDL-C of control group was significantly higher than that of the adding groups (P＜0.05).With the dietary cholesterol content increasing,the activity of malic enzyme (ME) in liver was increased,and that of C1.5,C2.0 and C2.5 group was significantly higher than that of the other groups (P＜0.05);the activity of carnitine acyltransferase Ⅰ (CPT Ⅰ) in liver had a downtrend and then to be stable,and that of control group was significantly higher than that of the other groups (P＜0.05);the activity of cholesterol 7α hydroxylase (CYP7A1) had a uptrend and then to be stable,and that of the C0.5 group was the highest and increased by 35.48％ than that of the control group (P＜0.05).In this experiment,base on the WGR and liver CYP7A1 activity as evaluation indices,the cholesterol requirement for the orange-spotted grouper determined by broken-line model analysis is 7.43 and 8.70 g/kg diet,respectively.