饲料中添加核苷酸对凡纳滨对虾幼虾生长、肠道形态及抗氧化酶活力的影响

Effects of dietary nucleotides on growth performance,intestinal mor-phology and anti-oxidative activities of juvenile Litopenaeus vannamei

本实验旨在研究外源核苷酸混合物对凡纳滨对虾(Litopenaeus vannamei)幼虾生长性能、体组成、中肠肠道形态和抗氧化酶活力的影响。选取960尾初始体质量为(1.01±0.02)g的凡纳滨对虾,随机分为8组,分别投喂基础饲料和添加5种核苷酸混合物(5′-腺苷酸∶5′-胞苷酸∶5′-尿苷酸二钠∶5′-肌苷酸二钠∶5′-鸟苷酸二钠=1∶1∶1∶1∶1,mix-NT)的实验饲料,各实验组添加量分别为0.1、0.2、0.4、0.6、0.8、1.0和1.2 g/kg饲料,养殖期为7周。结果显示,饲料中添加5种核苷酸混合物对凡纳滨对虾的特定生长率(SGR)和饲料系数(FCR)影响不显著(P>0.05)。外源核苷酸显著影响凡纳滨对虾全虾水分含量(P<0.05),但对全虾粗蛋白、粗脂肪和灰分含量影响不显著(P>0.05)。肝胰指数(HSI)随饲料中核苷酸添加量的增加而显著升高(P<0.05),在0.6 g/kg组达到最高。0.4 g/kg组的肝胰腺谷草转氨酶(GOT)和谷丙转氨酶(GPT)活力及尿酸(UA)含量最低,但与对照组相比差异均不显著(P>0.05)。中肠肠壁厚度和肠绒毛高度均随着核苷酸添加量的增加呈先升高后降低的趋势,其中添加量为0.1～0.8 g/kg组的肠壁厚度显著高于其他组(P<0.05);各组间的肠绒毛高度无显著性差异(P>0.05)。饲料中添加核苷酸混合物可显著提高凡纳滨对虾肝胰腺碱性磷酸酶(AKP)活力和总抗氧化能力(T-AOC)(P<0.05),两者的最高值分别出现在0.2 g/kg组和0.4 g/kg组。各添加组血清碱性磷酸酶(AKP)和超氧化物歧化酶(SOD)活力与对照组相比差异均不显著(P>0.05)。结果表明,饲料中添加一定量的5种核苷酸混合物有助于改善凡纳滨对虾肠道形态,增强机体的抗氧化能力。

There has been extensive research into the role of nucleotides and their related metabolic products in aquatic feeds.Nucleotides and metabolites play key roles in many biological processes and are considered condi-tionally essential nutrients.During periods of rapid growth or certain disease states,dietary nucleotides may spare the cost of de novo nucleotides synthesis and optimize the function of rapidly dividing tissues,such as those in the gastrointestinal and immune systems.Research on dietary nucleotides in aquatic animals has illustrated that they may improve diet palatability,enhance growth in early stages of development,and maintain intestinal and liver health,as well as increase immunity and disease resistance.Despite their apparent importance,little is known about the benefits of supplementary nucleotides in Litopenaeus vannamei.We evaluated the effects of dietary nu-cleotides on growth,body composition,midgut morphology,and anti-oxidant activity in the hepatopancreas and serum in juvenile L.vannamei.We randomly assigned 960 shrimp（mean body weight： 1.01 g±0.02 g） into 8 trip-licate groups.Group G0（control） was fed a base diet and the remaining seven groups（G0.1,G0.2,G0.4,G0.6,G0.8,G1.0,and G1.2） were fed the base diet supplemented with 0.1,0.2,0.4,0.6,0.8,1.0,or 1.2 g/kg,respec-tively,of a nucleotide mixture containing adenosine-5′-monophosphate（AMP）,cytidine-5′-monophosphate（CMP）,uridine-5′-monophosphate disodium salt（UMP）,inosine-5′-monophosphate disodium salt（IMP）,and guanosine-5′-monophosphate disodium salt（GMP）（1 ： 1 ： 1 ： 1 ： 1 w/w,mix-NT）.All groups were fed their re-spective diets three times a day（8：00,15：00,and 20：00） at the same fixed rate,which ranged from 4% to 6% of body weight,for 7 weeks.Specific growth rate（SGR） and survival（SR） tended to increase as the concentration of the dietary mix-NT increased,peaking in the group supplemented with 0.6 g/kg,though the differences among the groups were not significant（P〉0.05）.The feed conversion rate（FCR） was lower in the treatment groups than in the control group,but not significantly（P〉0.05）.The whole body moisture content was significantly affected by the level of dietary mix-NT supplementation（P〈0.05）,but there were no significant differences in the content of crude protein,ether extract,or ash（P〉0.05）.The dietary mix-NT had a significant effect on the hepatosomatic index（HSI） in the group supplemented with 0.6 g/kg（P〈0.05）.Glutamic-oxaloacetic transaminease（GOT）,glu-tamic-pyruvic transaminase（GPT）,and uric acid（UA） content were significantly lower in shrimp fed 0.4 g/kg mix-NT（P〉0.05）.There was a significant increase in the midgut jejunum wall thickness in shrimp fed 0.1–0.8 g/kg mix-NT,but there no significant difference in villus height of all groups.Alkaline phosphatase（AKP） activity and total antioxidant capacity（T-AOC） in the hepatopancreas tended to increase as the level of supplementation with dietary mix-NT increased,and were significantly higher in groups G0.2 and G0.4,respectively,than in the control（P〈0.05）.Adding mix-NT had no significant effect on serum alkaline phosphatase（AKP） and superoxide dismutase（SOD） activity（P〉0.05）.In conclusion,supplementing the diet with a mixture of 5 nucleotides im-proves hepatopancreas function,maintains intestinal morphology,and enhances anti-oxidant activity in the hepa-topancreas of juvenile L.vannamei.It would be interesting to determine the effects of nucleotide supplementation on immune function,particularly with respect to white spot syndrome virus（WSSV）.