Affecting mechanism of Chlorella sorokiniana meal replacing fish meal on growth and immunity of Litopenaeus vannamei based on transcriptome analysis

The purpose of this study was to analyze the affecting mechanism of Chlorella sorokiniana meal replacing fish meal on the growth performance and immune function of Pacific white shrimp, Litopenaeus vannamei by transcriptomics analysis. In a control diet containing 560 g % /kg fish meal, chlorella was used to replace 0 %, 20 %, 40 %, 60 %, 80 % and 100 % of dietary fish meal to form six iso-nitrogenous and iso-lipidic diets (C0, C20, C40, C60, C80, C100). The six diets were fed to white shrimp (1.37 ± 0.02 g) for 8 weeks. Compared to the control group, the final body weight (FBW), specific growth rate (SGR) and feed efficiency (FE) of the C20 group were significantly improved (P < 0.05). There was no significant difference in growth performance between the C40 group and the C0 group (P > 0.05). When the replacement level of fish meal by chlorella was ≥ 60 %, the FBW, SGR and FE of shrimp were significantly decreased (P < 0.05). In the analysis of the hepatopancreatic transcriptome, the amount of differentially expressed genes (DEGs) in C20, C40, C60, C80 and C100 groups were 322 (176 up and 146 down), 482 (246 up and 236 down), 804 (487 up and 317 down), 1080 (684 up and 396 down) and 1262 (827 up and 435 down), respectively, when compared to the C0 group. GO Term and KEGG pathway enrichment analysis of DEGs showed that DEGs between the C20 and C0 groups were significantly enriched in chitin binding and inositol metabolism processes. Several immune-related signaling pathways were also enriched, including the C-type lectin receptor pathway, complement and coagulation cascades, the B-cell receptor pathway, and most of these genes were up-regulated in the C20 group. Compared to the C0 group, DEGs in C40, C60, C80 and C100 groups were significantly enriched in lysosomal, protein digestion, and absorption pathways. In addition, in the C80 and C100 groups, the DEGs were also significantly enriched in lipid catabolism process. The high replacement of fish meal with chlorella meal affected the absorption and utilization of nutrients by regulating the signaling pathways related to protein digestion and absorption, and aggravated lipid catabolism of the body, thereby affecting the growth of shrimp. The high replacement of fish meal might also affect the homeostasis of shrimp cells and reduce immunity through the lysosomal signaling pathway. In summary, the low replacement of fish meal (20 %) with chlorella meal significantly improved the growth performance of Litopenaeus vannamei, which might be realized through activating the C-type lectin receptor signaling pathway to regulate immune function of the body, but the high substitution of fish meal (≥ 60 %) reduced the growth performance and immunity by affecting the lysosomal signaling pathway.