Effects Of Replacing Sargassum Sp. With Ulva Lactuca And Degummed Laminaria Japonica In Fermented Feed On The Growth,Digestive Enzymes,and Body Composition Of Sea Cucumber(Apostichopus Japonicus)

Apostichopus japonicus is one of the important aquatic economic animals in China.Because of its higher nutritional and medicinal values,it has been popular for consumers in our country since ancient times,and the huge market demand promote the development of A.japonicus aquaculture industry.Under natural conditions,A.japonicus mainly feeds on bacteria,fragments of various algae,single-celled algae,protozoa,organic compound in sediment.With the continuous improvement of culture scale and culture technology,the natural food can no longer meet the nutritional requirements of A.japonicus,and exogenous supplementation of formulated feeds has gradually become the key to solve this problem.Sargassum sp.are important ingredients of formulated feeds for A.japonicus,accounting for up to 40%.Due to the fast development of A.japonicus culture industry,Sargassum sp.resources have been overexploited worldwide,resulting in increasing costs,unstable supply and other problems.Therefore,it is urgent to find the alternative algae of Sargassum sp.to ensure the sustainable development of A.japonicus industry.This study was conducted to evaluate the application effect of Ulva lactuca and Degummed Laminaria japonica to replace Scagassum sp.from the perspective of growth performance,digestive enzyme activities and body wall nutritional composition.It will provide theoretical basis for formulating efficient and effective feeds for A.japonicus.The main research results of this paper are as follows:(1)Effects of replacing Sargassum sp.meal with Ulva Lactuca meal in the fermented feeds on the growth,digestive enzyme activities and body composition of A.japonicus.Feeds were formulated by replacing Sargassum sp.meal with different level(0%,33.3% and 50%)of Ulva Lactuca meal and then fermented with Lactobacillus lactis or/and Clostridium butyricum,which were named SL,SC,SUL,SUC,SULC,respectively.Each feed was randomly allocated to three tanks of A.japonicus with the initial body weight of 7.61±0.92 g.The feeding experiment lasted for 60 days.The results showed that the weight gain rate of the SUC group was 178.70%,which was significantly higher than that in the other four groups(P < 0.05).The body wall weight,intestinal weight,intestinal length and width were highest in the SUC group,which showed no significant differences with other dietary groups(P > 0.05).There were no significant differences in the lipase and trypsin activities between dietary groups(P > 0.05).The crude protein content of the body wall in the SULC group was the highest,which was significantly higher than that in the other four groups(P > 0.05).The crude fat content of body wall in SUC groups was the highest,and significantly higher than that in SL and SC groups(P < 0.05).These results showed that replacing Sargassum sp.meal with 33.3% Ulva lactuca meal and using Clostridium butyricum as fermented bacteria(SUC)significantly promoted the growth performance without negatively affecting the body composition of A.japonicus.(2)Effects of replacing Sargassum sp.meal with degummed kelp meal in fermented feeds on the growth,digestive enzyme activities and body composition of A.japonicus.In this experiment,three feeds were formulated by replacing Sargassum sp.meal with different level of degummed kelp meal(0%,33.3%,50%),which were named KP0,KP33,KP50,respectively.Each feed was randomly allocated to three tanks of A.japonicus with the initial body weight of 7.54±0.15 g.The feeding experiment lasted for 45 days.The results showed that the final weight and weight gain rate of the control group were the highest,which were comparable to those in the KP50 group(P >0.05).The body length,body width and body wall weight in the KP50 group were significantly higher than those in the other two groups(P < 0.05).The intestinal weight and intestinal length of A.japonicus in KP50 group were significantly higher than those in the other two groups(P < 0.05).There were no significant differences in the activities of lipase,trypsin and amylase between dietary groups(P > 0.05),with the highest lipase and trypsin activities observed in the KP50 group.There was no significant difference in the proximate composition of body wall of A.japonicus(P >0.05).These results showed that 50% Sargassum sp.meal can be replaced by degummed kelp meal in the fermented feeds without negatively affecting the growth,digestive enzyme activities and body composition of A.japonicus.