Assessment on Chlorella (Chlorella sorokiniana) meal as a substitution for fishmeal in Songpu mirror carp (Cyprinus carpio Songpu) feed: Effect on growth, intestinal health and microflora composition

The experiment aims to investigate Chlorella (Chlorella sorokiniana) replaced fishmeal on growth performance, blood biochemical indices and intestinal health of juvenile Songpu mirror carp (Cyprinus carpio Songpu). Chlorella was substituted for 0 % (G1), 30.0 % (G2), 58.3 % (G3) and 88.3 % (G4) of fishmeal (6 %) in the basal diet. Diets were fed in triplicated groups of Songpu mirror carp with an initial body weight of 5.50 +/- 0.03 g/fish for 8 weeks. Results showed that the final body weight and specific growth rate increased significantly in G3, and the feed conversion ratio was significantly lower than in G4. The serum albumin content in G3 was significantly higher than in G4; alanine aminotransferase content was significantly higher than remaining groups except G4. Malondialdehyde content decreased significantly with increasing level of substitution. The intestinal villi of G1 and G3 were in the optimal tissue state, neatly arranged and without shedding. The expression levels of genes associated with intestinal protein synthesis (growth hormone, phosphatidylinositol 3 kinase, protein kinase b, s6 kinase), antioxidant (catalase, glutathione peroxidase 1a) and immune (zonula occluden 1, claudin7, claudin11) were significantly higher in G3 than in G1; the intestinal inflammatory factor Interleukin-1 beta (IL-1 beta) was significantly lower than G1. The substitution group decreased the relative abundance of Ascomycetes and Actinobacteria phylum and increased the percentage of Firmicutes. This study indicated that Chlorella was substituted for 58.3 % of fishmeal, it could significantly improve the growth performance, enhance the protein metabolism level and promote the development of intestinal morphology and immunity of Songpu mirror carp.