Stocking density induces differential expression of immune-related genes in skeletal muscle and head kidney of fine flounder (Paralichthys adspersus)

•The expression of several immune-related genes in fish skeletal muscle were downregulated under chronic stress conditions.•The expression of the same immune-related gene expression in head kidney were upregulated under chronic stress conditions.•The crowding stress may adversely affect normal muscle function. Immunity can be modulated by different internal and external factors, being stress one of the most important. However, the stress effects on the immunocompetence of the skeletal muscle has not been studied in detail in earlier vertebrates. Here, we examine the effect of chronic (4 and 7 weeks) crowding stress on the immunocompetence of skeletal muscle and head kidney in the fine flounder (Paralichthys adspersus). Corticosteroid receptor transcript levels and their target genes; pro-inflammatory cytokines, and Toll-, NOD-, and RIG-like receptors were quantified by qPCR. The results indicate that chronic stress down-regulates the expression of these genes in muscle, compromising skeletal muscle immunocompetence, while the expression of these genes is upregulated in head kidney after seven weeks of crowding stress. The data suggests that chronic stress modulates the expression of these immune-related genes in a tissue-specific manner.