Study On The Application Effect Of Defatted Schizochytrium Sp. In Feed For Three Carps

Schizochytrium sp.is a type of marine microalgae belonging to Eumycota and Thraustochytriaceae.It is rich in docosahexaenoic acid（DHA）,its algae meal and oil can be used as a source of high-quality n-3 long-chain polyunsaturated fatty acids in aquatic feed（Ryckebosch et al.,2014）.Defatted Schizochytrium sp.is a by-product of DHA extraction.It is in the form of black fragments and still contains DHA,protein,minerals and biologically active compounds.In this study,three carps,mirror carp（Cyprinus carpio var.specularis）,grass carp（Ctenopharyngodon idella）,and Onychostoma macrolepis were used as research objects to evaluate the effects of Defatted Schizochytrium on its growth,body composition,fatty acid composition,antioxidant properties,and lipid metabolism.It aims to provide basic information for the utilization of by-products of Schizochytrium sp.microalgae industry and the development of aquatic feed.Trial 1 Study on the application effect of detatted Schizochytrium（DS）in the feed of mirror carp.Five practical isonitrogenous（38.00%）and isolipid（5.60%）diets were prepared,and 0 g kg^-1（Control）,30g kg^-1（DS3）,60g kg^-1（DS6）,90g kg^-1（DS9）and 120g kg^-1（DS12）of DS,fed with five groups of mirror carps,respectively（8.55±0.05g/tail,18tails/cage）56 days.The results showed that:（1）The final weight（FBW）,weight gain rate（WGR）and specific growth rate（SGR）of the DS12 group fish were significantly lower than those of the control group（P<0.05）;（2）The content of crude protein（CP）in whole fish and liver in DS6 and DS9 group was significantly higher than that in the control group（P<0.05）,and the content of crude lipid（CL）was significantly lower than that in the control group（P<0.05）;（3）DS6,DS9 and The contents of DHA and n-3 LC PUFA in muscle,liver and whole body in the DS12 group were significantly higher than those in the control group（P<0.05）;（4）Atherosclerosis index（AI）and thrombosis index（TI）of muscles in all treatment groups were significantly lower than the control group,while the low-cholesterol/high-cholesterol fatty acid ratio（h/H）index was significantly higher than that of the control group（P<0.05）;（5）The height of fore-intestinal villi in the DS3 and DS6groups was significantly higher than the control group（P<0.05）;（6）The serum and liver superoxide dismutase（SOD）activities of DS6,DS9 and DS12 groups were significantly higher than those of the control group（P<0.05）.Studies have shown that the addition of 6%DS in the feed can improve the growth performance of the mirror carp,reduce the CL of the whole body and liver,improve the body’s antioxidant capacity and the nutritional value of muscle,and increase the n-3 LC PUFA.This study believes that DS can be successfully used in the diet of mirror carp.Trial 2 Study on the application effect of detatted Schizochytrium（DS）in grass carp feed.Five practical isonitrogenous and isolipid diets were prepared,and 0 g kg^-1（Control）,30g kg^-1（DS3）,60g kg^-1（DS6）,90g kg^-1（DS9）and 120g kg^-1（DS12）of DS,fed with five groups of mirror carps,respectively（37.55±0.55g/tail,12 Tail/cage）56 days.The results showed that:（1）The food intake rate（FR）in all treatment groups（DS3,DS6,DS9 and DS12）was significantly higher than that of the control group（P<0.05）;（2）HSI in DS6,DS9and DS12 groups and IPFI were significantly lower than those of the control group（P<0.05）;（3）The CP in the whole body and liver of the DS6 and DS9 groups was significantly higher than that of the control group,while the CL was significantly lower than the control group（P<0.05）;The mRNA expression of mTOR gene in liver of the DS3 group was significantly higher than that of the control group（P<0.05）;（4）The average area of adipocytes in all treatment groups was significantly smaller than that of the control group,while the number of hepatocytes per unit area was significantly higher than that of the control group（P<0.05）;（5）The DHA content in muscle and liver of DS6,DS9 and DS12 groups was significantly higher than that of the control group（P<0.05）;（6）The expression levels of liver lipid synthesis gene ACC1 mRNA in all treatment groups were significantly down-regulated,and the mRNA expression levels of lipolysis-related genes ATGL,HSL and PPARαin DS6,DS9,and DS12 were significantly decreased;the abdominal fat ACC1 and ACC1 in DS6,DS9and DS12 groups FAS mRNA expression was significantly lower than the control group,while the mRNA expressions of ACC2,ATGL,and CPT1 were significantly higher than the control group（P<0.05）.Studies have shown that the addition of 9%(90g kg^-1)of DS in the diet can improve grass carp feeding,reduce its fat accumulation,increase the accumulation of DHA in the fish,and then increase the nutritional value of muscle,and will not affect the growth and antioxidant status.This study confirmed that the DS can be successfully used in the diet of grass carp.Trial 3 Study on the application effect of detatted Schizochytrium（DS）in Onychostoma macrolepis feed.Adding 0g kg^-1（DS0）,30g kg^-1（DS3）,60g kg^-1（DS6）,90g kg^-1（DS9）and120g kg^-1（DS12）DS to five diets,a 56-day breeding test was carried out on O.macrolepis（9.00g±0.25g/tail,12 tails/tank）.The results showed that:（1）The CF of the DS9and DS12 groups was significantly lower than that of the control group（P<0.05）;（2）The HSI and IPFI of the DS6,DS9 and DS12 groups were significantly lower than the control group（P<0.05）);CL content in muscle of all treatment groups（DS3,DS6,DS9 and DS12）was significantly lower than that of the control group（P<0.05）;（3）The triglyceride content of liver and intraperitoneal fat in DS9 and DS12 groups was significantly lower than that of the control group（P<0.05）;（4）The content of DHA in the muscle and liver of the DS6,DS9and DS12 groups were significantly higher than those in the control group（P<0.05）;（5）The number of hepatocytes per unit area of liver in DS9 and DS12 groups was significantly higher than that in the control group;the height of fore-intestinal villi in all treatment groups was significantly higher than that in the control group,and the average number of adipocytes per unit area of abdominal adipose tissue The area was significantly smaller than that of the control group（P<0.05）;（6）The mRNA expression levels of FSA and ACC1 in the liver of all treatment groups were significantly higher than those of the control group.FSA,ACC1,and SREBP-1 in the intraperitoneal fat of the DS6,DS9 and DS12 groups The mRNA expression level of ACC2 and ATGL was significantly lower than that of the control group,while the mRNA expression levels of ACC2 and ATGL were significantly higher than that of the control group（P<0.05）;（7）The MDA content in liver of DS3,DS6 and DS9 groups was significantly lower than that of the control group（P<0.05）).The research results show that adding 9%(90g kg^-1)of DS in the diet can significantly increase the content and nutritional value of n-3 LC PUFA in fish,enhance the body’s antioxidant status,and significantly reduce fat accumulate and regulate the expression of genes related to lipid metabolism.This study confirmed that DS can be successfully used in the diet of O.macrolepis.