Transcriptomics, antioxidant enzyme activities, and immune-associated parameter analysis reveal the molecular responses of rainbow trout (Oncorhynchus mykiss) to transportation stress

To explore how transportation stress affects the physiology of rainbow trout, we measure antioxidant and immunity-related indicators in spleen tissues of adult fish during transportation (at 0, 2, and 6 h) and 24 h following it (r24 h). We report a significant reduction in spleen catalase activity among the 2, 6, and r24 h groups compared with the 0 h group (P < 0.05). Levels of glutathione peroxidase activity and total antioxidant capacity, and lipid peroxide, complement C4, and immunoglobulin M contents first decreased, then increased; complement C3 content and lysozyme activity first increased, then decreased; and tumor necrosis factor-α levels were relatively stable (P > 0.05). Transcriptome sequencing of spleen samples at 0, 6, and r24 h using Illumina HiSeq6000 identified 4419, 2733, and 4375 differentially expressed genes (DEGs) in 0 vs 6, 6 vs r24, and 0 vs r24 h comparisons, respectively. Gene ontology annotation of these DEGs revealed them to function mainly in binding and catalytic activities, and to be significantly enriched in cellular processes and biological regulation terms. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed DEGs in the 0 h vs 6 h comparison to be significantly enriched in cytokine–cytokine receptor interaction, C-type lectin receptor signaling pathway, in regulating actin cytoskeleton, lysosome (0 vs r24 h); and in the Toll-like and MAPK signaling pathways (6 vs r24 h). Several immune-related genes were identified from both the 0 h vs 6 h and 6 h vs r24 h comparisons. These findings lay a solid foundation for further research on understanding how fish respond to transportation stress at the molecular level.