Gill histology, biochemistry and transcriptomics analyses reveal alleviation of dietary arginine supplementation on transport stress of Culter alburnus.

The transport process usually causes fish stress and induces physiological perturbations and tissue structural damage. Arginine, an essential amino acid for fish, plays a significant role in immune regulation. In this work, we investigated the effect of arginine on alleviating transport stress of Culter alburnus. The diets with arginine levels of 1.96% (CON group) and 2.52% (ARG group) were fed to C. alburnus for 70 days, followed by a 24-h simulated transport. The groups were defined as follows: non-transported control (CON0h), non-transported arginine (ARG0h), transported control (CON24h), and transported arginine (ARG24h). The results showed that dietary arginine significantly reduced the levels of NH3-N and NO2--N in the transport water, increased the enzyme activities of GSH, AKP, and NOS, and decreased the content of MDA after transport (P < 0.05). The ARG group had significantly thinner primary gill lamellae and longer secondary gill lamellae than the CON group (P < 0.05). Transcriptome sequencing identified a total of 1190 differentially expressed genes (DEGs: 755 up, 435 down) between CON24h and ARG24h. KEGG enrichment indicated that arginine alleviated transport stress mainly by enhancing immune response and inhibiting inflammatory response, such as CD9, CFB were significantly up-regulated, and CCL20 was significantly down-regulated. In summary, dietary arginine enhanced the antioxidant and immune response of C. alburnus, reducing inflammation after transport. The present study demonstrates that arginine has a positive impact on alleviating transport stress in C. alburnus, which may be used as a dietary supplement to alleviate stress in live fish during transport.