Effects Of Replacing Sargassum Sp. With Wheat Bran And Sweet Potato Vine In Fermented Feed On The Growth,Digestive Enzyme Activity,and Body Composition Of Sea Cucumber(Apostichopus Japonicus)

Sea cucumber(Apostichopus japonicus)is an important economic aquatic animal species in China,which has attracted more and more attention because of its high nutritional and medicinal value.This makes the demand for sea cucumbers increase year by year,which in turn promotes the development of the sea cucumber farming industry.Formulated feeds are important foundation and guarantee for the sustainable development of sea cucumber farming industry.Sargassum sp.is traditionally used as the feed ingredients for sea cucumber farming.In the last decades,the natural resource of Sargassum sp.has declined seriously due to overexploiting worldwide.This,to a large extent,increased the feed cost of sea cucumber farming.Therefore,it is particularly important to find new land plant substitutes for Sargassum sp.to ensure the sustainable development of sea cucumber farming industry.Thus,two studies were conducted to investigate the effects of replacing Sargassum sp.meal with wheat bran or sweet potato seedling meal on growth performance,digestive enzyme activities and body composition of A.japonicus.It was expected to provide basic information for formulating efficient and environmentally friendly feeds for A.japonicus.The main results are as follows:(1)Effects of replacing Sargassum sp.meal with wheat bran meal in fermented feed on the growth,digestive enzyme activities and body composition of sea cucumbers.In this study,different proportions of wheat bran meal(0%,33%,50% and 100%)were used to replace Sargassum sp.meal in the basic feed,which were named WB0,WB33,WB50 and WB100,respectively.Each feed was randomly allocated to three tanks of A.japonicus with an initial body weight of 7.31±0.34 g.The experimental period lasted for 40 days.The results showed that partial or complete substitution of Sargassum sp.with wheat bran did not significantly affect the survival rate of sea cucumbers(P>0.05).The final body weight and specific growth rate of sea cucumbers in the WB33 group were the highest,which were not significantly different from those in the WB50 group(P>0.05),but were significantly higher than those in the WB0 and WB100 groups(P<0.05).The intestine length of the sea cucumber in the WB50 group were significantly higher than in the other groups(P<0.05).As the wheat bran inclusion level increased,the crude protein and crude lipid content in the body wall first increased and then decreased,with the highest value observed in the WB33 or WB50 group.Partial or complete substitution of Sargassum sp.with wheat bran in the diet increased the digestive enzyme activities in the intestine of sea cucumbers to some extent,but significant differences were only observed between the WB100 and WB0 groups for lipase activity(P<0.05).In conclusion,moderate substitution of Sargassum sp.with wheat bran in the fermented feed has a promoting effect on the growth of sea cucumbers.Based on the growth performance and nutritional composition,the optimal substitution level of Sargassum with wheat bran was estimated to be33%-50% for juvenile A.japonicus.(2)Effects of replacing Sargassum sp.meal with sweet potato vine meal in fermented feed on the growth,digestive enzyme activity and body composition of sea cucumber.In this study,different proportions(0%,33%,50% and 100%)of sweet potato vine meal were used to replace Sargassum sp.meal in the basic feed,which were named SPV0,SPV33,SPV50 and SPV100,respectively.Each feed was randomly allocated to three tanks of A.japonicus with an initial body weight of 14.76±1.17 g.The experimental period lasted for 30 days.The results showed that there was no significant difference in the survival rate among the four experimental groups(P>0.05).In this study,the final body mass,weight gain rate and specific growth rate of A.japonicus in SPV33 group were significantly higher than that in the other three groups(P<0.05).Replacement of Sargassum sp.meal with sweet potato vine meal showed no significant effects on the body length of A.japonicus(P>0.05).However,the body width of SPV0 group was significantly higher than that of SPV50 and SPV100 groups(P<0.05).There were no significant differences in the intestine length,intestine width,intestine weight among dietary groups(P>0.05).Replacement of Sargassum sp.with sweet potato vine significantly affect the crude protein and crude lipid(P<0.05),but had no significant effects on the moisture content of A.japonicus(P>0.05).The crude protein content of sea cucumbers body wall in SPV0 group was the highest,which was significantly higher than that in SPV33 group(P<0.05).The crude lipid content of sea cucumber body wall was highest in the SPV0 group,which was significantly higher than that in the other three groups(P<0.05).There was no significant difference in trypsin and amylase activities among experimental groups(P>0.05).The lipase activity was highest in the SPV0 group,which was significantly higher than that in the SPV50 and SPV100 groups(P<0.05),but was comparable to that in the SPV33 group(P>0.05).In conclusion,the growth and digestive enzyme activities were not significantly affected or even improved by replacing Sargassum sp.meal with sweet potato vine meal at appropriate level.Based on the growth performance and digestive enzyme activities,the optimal substitution level of Sargassum sp.with sweet potato vine was estimated to be 33% for juvenile A.japonicus.