Effect Of Feeding With Compound Feed Instead Of Chilled Fish On Growth Performance And Nutritional Quality Of Chinese Mitten Crab

The Chinese mitten crab(Eriocheir sinensis)is an important economic crab species in China.The common diet is chilled wild fish.However,there are many problems in feeding chilled fish to Chinese mitten crab,such as its source is easily constrained by the source and season,low diet conversion efficiency,and its own perishability to pollute the culture environment,etc.These problems become one of the important factors limiting the sustainable development of Chinese mitten crab culture.In view of this,this study was conducted with Chinese mitten crab as the research object,with chilled fish diet group(CHF)and compound feed group(6681,BXW),totaling three experimental groups(three parallel groups each).The experiment was conducted to replace chilled fish with compound feed for Chinese mitten crab culture for 75 d.The main results were as follows.The main results of the study are as follows:1.Effect of feeding chilled fish instead of compound feed on the growth performance of Chinese mitten crabThe survival rate of Chinese mitten crab in both the 6681 and BXW groups was significantly higher than that of the CHF group(P < 0.05).The weight gain rate of Chinese mitten crab in both the CHF and BXW groups was better and significantly better than that of the 6681 group.The diet coefficients of Chinese mitten crab in the BXW,6681 and CHF groups were 1.76,2.75 and 9.43 respectively,with the diet coefficients of the compound feed groups(BXW,6681)being significantly lower than that of the CHF group(P < 0.05),6681)were significantly lower than the CHF group(P < 0.05).There were no significant differences in hepatopancreas index and meat yield among the three groups of Chinese mitten crab.Under the condition that only diet cost was considered,the return on investment was predicted to be 8.10 and 6.76 times higher for 6681 and BXW than CHF,respectively.The results of the antioxidant analysis showed that in the hepatopancreas tissue,there were no significant differences in SOD activity,CAT activity and MDA content among the three groups of crabs.the T-AOC activity of crabs in the CHF group was significantly lower than that of the 6681 and BXW groups(P < 0.05),and there was no significant difference in T-AOC activity between the 6681 and BXW groups.In the haemolymph,the SOD activity,CAT activity and MDA content of the haemolymph of crab in the CHF group were significantly higher than those in the 6681 and BXW groups(P < 0.05),and there was no significant difference between the 6681 and BXW groups.There was no significant difference in T-AOC activity in the haemolymph of all three experimental crab groups.Analysis of hepatopancreas digestive enzyme activity showed that the pepsin activity was significantly higher in the BXW and CHF groups than in the 6681 group(P < 0.05),with no significant differences between the BXW and CHF groups.There was no significant difference in lipase activity between the three groups.α-amylase activity was significantly higher in both the 6681 and BXW groups than in the CHF group(P < 0.05),but there was no significant difference between the 6681 and BXW groups.2.Effect of feeding chilled fish instead of compound feed on the intestinal microorganisms of Chinese mitten crabThe results showed that there was no significant difference in the gut microbial composition of Chinese mitten crab,with a total of 447 OTUs in the gut of the three groups of Chinese mitten crab.At the phylum level,the dominant phyla in the intestinal flora of Chinese mitten crab were Tenericutes,Proteobacteria and Actinobacteriota;at the genus level,the dominant genera in the intestinal tract of the three groups were Candidatus Alpha diversity analysis showed no significant differences in Chao1,Observed species,Shannon and Simpson indices.beta diversity analysis showed that the samples showed food aggregation.Functional predictions showed that the functions of the gut microflora of the three Chinese mitten crab groups were focused on biosynthesis,mainly including amino acid biosynthesis,carbohydrate biosynthesis and cell structure biosynthesis.3.Effect of feeding chilled fish instead of compound feed on the nutritional quality of Chinese mitten crabAnalysis showed no significant differences in crude nutrients,total free amino acids and total flavouring amino acids and ∑SFA,∑MUFA,EPA,DHA,∑PUFA,∑HUFA,∑n-3PUFA,n-3/n-6 in the muscle and hepatopancreas of the three groups of Chinese mitten crab.Taken together,it can be concluded that the compound feed can completely replace the chilled fish without affecting the quality of its edible parts.In summary,the growth performance of Chinese mitten crab fed with low protein compound feed was lower than that of chilled fish,while the high protein feed gave the crab similar growth performance and nutritional quality to that of the chilled fish group.Secondly,the antioxidant capacity of the crab in the compound feed group was higher than that of the chilled fish group,which effectively reduced oxidative damage,improved immunity and reduced disease occurrence.Furthermore,the economic benefits of feeding Chinese mitten crab with compound feed were much higher than those of feeding chilled fish.Therefore,it is possible to replace chilled fish with high quality commercial feeds in aquaculture without affecting the growth,fitness,nutritional quality and economic benefits of Chinese mitten crab,and this has positive implications for reducing pollution of the aquaculture water and ecological environment.