Effect Of Vitamin C On Growth And Non-specific Immunology Of Sea Cucumber, Apostichopus Japonicus

The sea cucumber Apostichopus japonicus is one of the most valuable mariculture species in north China.In recent years,the rapid expansion and intensification of sea cucumber farming has led to the occurrence of various diseases,causing serious economic losses and becoming one of the limiting factors in the sustainable development of this industry.Although the use of antibiotics has gained certain effects in treating diseases and pathogens,the concomitant negative effects have been discovered evidently.At present,the applications of immunity stimulants to maintaining high resistance to pathogen in aquculture species is a preferred method in modern aquaculture industry.While the vitamin C is one of the essential nutrients which could promote immune response and used extensively as immunity stimulant in many aquculture species.And this study is aimed to observe the effect and requirement of vitamin C on growth,non-specific immunity and resistance in A. japonicus juveniles. An analysis of activity of the emzyme L-gulonol-γ-lactone oxidase(GLO) in bodywall and viscera has shown that the GLO activity in A.japonicus is extremely low,which is 0.011～0.013μgAA/h·g tissue,only one millionth of that in a rat liver.This proves that A.japonicus is unable to de-nove synthesis of ascorbic acid because of lacking the GLO activity;hence its demand for vitamin C can only rely on dietary intake.An analysis of intestinal contents of wild A.japonicus has shown that the vitamin C level in the intestinal contents is quite high,is almost 108mg/kg,which reveals that the natural baits of A.japonicus are rich in vitamin C,and the vitamin C demand of A.japonicus could be satisfied by its feeding behavior.A 60 day feeding trial was carried out to study effect of 5 different dieatary vitamin C level on the growth and non-specific immnity of A.japonicus.Five piratical feeds was desighed to contain 0,500,1500,5000 and 15000 mg/kg vitamin C,with the form of L-ascobyle-polyphosphate(LAPP).The results showed that over 500 mg / kg vitamin C has significantly effect on weight gain and specific growth rate(P＜0.05).5000 mg / kg vitamin C can significantly reduce the vescera-bodywall ratio,accelerate collagen synthesis and improve the alkaline phosphatase(AKP) activity,acid phosphatase(ACP) activity,phagocytic rate and respiratory burst activity(P＜0.05);at the same time,A.japonicus fed with this dietary level also had better resisitance to Vibrio Splendidus challenge and higher bactericidal activity in both coelomic fluid and skin mucus(P＜0.05).While 15000 mg / kg vitamin C has significant positive effect on promoting coelomocyte count,agglutination titre,phenol oxidase activity and the lysozyme activity(P＜0.05).And the tissue ascorbic acid accumulation in A.japonicus has been seen increase with the increment of dietary vitamin C level.But during the whole feed trial,the effect of vitamin C on SOD activity was not obvious.However,the immunity promoting effect of vitamin C concerning most immune parameters could reach the peak in 20 d,and some immune tolerance phenomenon could be observered with continue feeding of vitamin C.Therefore,taking the above parameters of growth,immunity and resistance as evaluation indicators,the suitable vitamin C level in maintain growth is 500 mg/kg and the dietary vitamin C level as immunity stimulant should be over 5000 mg/kg in the form of LAPP.And the immune enhancing effect of dietary vitamin C in A.japonicus could reach its peak within 20 days.