Transcriptome analysis reveals the influence of anaesthetic stress on the immune system of crucian carp (Carassius auratus) under the process of treatment and low concentration transport by MS‐222 and Eugenol

Anaesthetics are widely used in aquaculture as a method of stress relief. However, few studies have reported the influence of anaesthetics on the immune system of fish. Therefore, in the present study, we selected two different anaesthetics, MS-222 (100 mg/L) and eugenol (20 mg/L), to anaesthetize crucian carp and analyse the transcriptome. It was found that over 137 million high-quality reads were generated and de novo assembled into a final set of 97,556 unigenes. A total of eight differentially expressed genes (DEGs) related to the immune response were co-expressed in the two anaesthetic groups. GO and the KEGG revealed that these genes functioned primarily to enrich antigen processing and presentation pathways, including MHCI, MHCI alpha, p-MHCII alpha, P-MHCII alpha, CD74, MHCII antigen and MHCII antigen alpha. Moreover, LRRFIP2 was found be associated with the immune response. Consistent with the transcriptome findings, qPCR verified the changes in the relative level of expression of these genes. Furthermore, long-term exposure to low concentrations of MS-222 (30 mg/L) and eugenol (8 mg/L) showed an impact on these immune genes. In conclusion, anaesthetics used in high or low concentrations for treatment and transport could affect the immune system in fish species. While eugenol was associated with an earlier activation of immune gene expression, MS-222 exhibited more significant effects on the immune response. These findings improve the understanding of the mechanisms of anaesthetics on immune damage and will be of great value for future studies involving anaesthetic selection and treatment for fish.