Effects of ecological polyculture of Micropterus salmoides and Hypophthalmichthys molitrix on their nutritional quality and intestinal microbiota

Objective This study aimed to explore effects of polyculture of Micropterus salmoides and Hypophthalmichthys molitrix on the growth， nutritional quality， and intestinal microbiota of Micropterus salmoides to identify the appropriate polyculture ratio and provide a scientific basis for exploring ecofriendly and healthy rearing models for Micropterus salmoides.Method In this experiment， Micropterus salmoides was polycultured with Hypophthalmichthys molitrix， and four treatment groups of Micropterus salmoides-Hypophthalmichthys molitrix ratios were set up： Micropterus salmoides single-culture group （K Group）， 18∶1 （L Group）， 9∶1 （M Group）， and 4.5∶1 （H Group）. The growth indexes， morphometric indicators， conventional nutritional components of muscle quality， amino acid content， fatty acid content， and texture characteristics were measured after the experiment. Intestinal contents were collected to extract DNA for intestinal microbiota sequencing， and population compositions under different taxonomic levels were statistically analyzed to conduct Alpha diversity， LEfSe， and correlation analyses were performed.Result Under polyculture models， no significant differences in growth indexes， muscle crude fat content， and water content were observed in the four groups of Micropterus salmoides （P>0.05）， the muscle ash contents in the M Group and L Group were significantly lower than those in the K Group （P<0.05， the same below）， and the muscle crude protein content in the M Group was significantly higher than that in the K Group. The four groups exhibited the optimal ratios for EAA/TAA in Micropterus salmoides muscle at 40%， the amino acid content in L Group was significantly higher than that in K Group， and the semiessential amino acid content in L Group was significantly higher than that in K Group， M Group， and H Group. In the amino acid evaluation and chemical evaluation of Micropterus salmoides muscle in the four groups， lysine was the essential amino acid with the highest scores， and the first limiting amino acid was methionine+cysteine. The monounsaturated fatty acid content in the K Group was the lowest， which was significantly lower than that in M Group， H Group， and L Group； the polyunsaturated fatty acid contents in L Group and M Group were significantly higher than that in the K Group. The EPA+DHA in M Group was significantly higher than that in the K Group. The atherogenic index and thrombosis index in the K Group were significantly lower than those in L Group， M Group， and H Group. Muscle resilience and cohesiveness in the M Group were significantly higher than those in the K Group. The ACE index and Chao index in the K Group and H Group were significantly higher than those in the L Group， and the Shannon index in the L Group was highly significantly lower than that in the K Group and M Group （P<0.01） and significantly lower than that in the H Group. The dominant phyla for the four Micropterus salmoides groups were Firmicutes， Actinobacteria， Proteobacteria， Cyanobacteria and so on； the dominant genera were Bacillus， Mycobacterium， Achromobacterium and so on.Conclusion The appropriate polyculture ratio of Micropterus salmoides and Hypophthalmichthys molitrix was 9∶1 and 18∶1， and applying an appropriate polyculture ratio could improve muscle quality through increasing contents of muscle crude protein， amino acid， umami amino acid， polyunsaturated fatty acid， C22：6， and C20：5， and maintain intestinal health through increasing abundances of beneficial microbiota such as Glutamicibacter and Pedobacter.