Effects Of Three Sea Mud Substitutes On Physiological State Of Apostichopus Japonicus Under Cadmium,Lead Stress

Apostiopsis japonicus feed mainly on the mud and debris of the sea floor.Cadmium(Cd)and lead(Pb)are toxic biological non-essential elements.Due to industrial activities,the coastal waters are acutely polluted by heavy metals.Among that,the contamination of sea mud by Cd and Pb has become an obstacle to the healthy development of sea cucumber farming.Three sea mud substitutes,montmorillonite,zeolite,and kaolin,were investigated for their effectiveness in inhibiting Cd or Pb poisoning in A.japonicus,and to study their future application in feed of A.japonicus.The main results are as follows:Trial 1 investigated the effects of three sea mud substitutes(montmorillonite,zeolite and kaolin)on growth,metabolic physiology,and Cd accumulation in tissues of A.japonicus under Cd stress.At the level of 50 mg/kg Cd,the SM group was used as the base diet(20% sea mud).The M,Z,and K groups were supplemented with 20% montmorillonite,zeolite,or kaolin instead of sea mud,respectively.Four diets were fed to A.japonicus(8.92±0.01g)for 21 days.The results showed that there was no significant difference in survival rate(SR)among all groups(P>0.05).The highest intestinal vomiting rate(IVR)was found in the Z group(P<0.05).Compared with the SM group,the weight gain rate(WGR),specific growth rate(SGR),daily feed intake(DFI),and feed conversion rate(FCR)in the M and K groups were not significantly different(P>0.05),while the growth performance and amylase activity(AMS)in the Z group were significantly inhibited(P<0.05).The malondialdehyde(MDA)content in the SM group was the highest(P<0.05).The activities of alkaline phosphatase(AKP),acid phosphatase(ACP),catalase(CAT),and superoxide dismutase(SOD)in the M and K groups were significantly higher than those in the SM group(P<0.05).There were no significant differences in the activities of alanine aminotransferase(ALT)and aspartate aminotransferase(AST)among all groups(P>0.05).The Cd accumulation in the intestinal tissues of A.japonicus was higher than that in the respiratory tree and body wall.The Cd accumulation in intestinal and respiratory tree tissues of A.japonicus in the M group decreased significantly(P<0.05),and the values of Cd accumulation in K group showed the downward trend.The Cd accumulation ratio in tissues of A.japonicus was M group < K group < SM group < Z group(P<0.05).In conclusion,feeding montmorillonite and kaolin reduced the accumulation of Cd in the tissues of A.japonicus,and inhibited the immune and antioxidant damage caused by dietary Cd toxicity.Trial 2 investigated the effects of three sea mud substitutes(montmorillonite,zeolite and kaolin)on growth,metabolic physiology,Pb accumulation in tissues and intestinal health of A.japonicus under Pb stress.At the level of 100 mg/kg Pb,the SM group was used as the base diet(20% sea mud).The M,Z,and K groups were supplemented with 20% montmorillonite,zeolite or kaolin instead of sea mud,respectively.Four diets were fed to A.japonicus(7.75±0.03 g)for 30 days.The results showed that there were significant differences in growth performance among all groups(P>0.05).Compared to the SM group,the remaining three groups showed significantly lower MDA content(P<0.05)and significantly higher SOD activity(P<0.05).ACP,AKP and CAT activities were significantly higher in the M and K groups than in the SM group(P<0.05),and the Z group showed the same trend.The highest ALT and AST activities were observed in the SM group(P<0.05).The results of Pb accumulation in tissues of A.japonicus showed that the SM group had the highest Pb accumulation in the body wall(P<0.05)and the M group had the highest Pb accumulation in the respiratory tree(P<0.05).The Pb accumulation ratio in A.japonicus tissues in the M,Z and K groups was significantly lower than that in the SM group(P<0.05).Compared to the SM group,the other three groups showed reduced the abundance of Proteobacteria and intestinal microflora α-diversity and reduced intestinal pathological damage of A.japonicus.In conclusion,kaolin,zeolite,and kaolin as sea mud substitutes inhibited the metabolic damage caused by dietary Pb to A.japonicus,reduced the accumulation of Pb in the body wall,optimized the structure of intestinal microflora,thereby reduced pathological damage to the intestine.