Effects of environmental salinity, biopsy, and GH and IGF-I administration on the expression of immune and osmoregulatory genes in the gills of Atlantic salmon (Salmo salar)

Abstract

Immune-endocrine interactions are thought to be important for fish health, especially following injury of peripheral tissues. We investigated the influences of gill biopsy (surgical removal of several gill filaments with minimal bleeding) on mRNA levels of osmoregulatory and immune genes in peripheral tissues of Atlantic salmon (Salmo salar) smolts in freshwater (FW) and seawater (SW). The effects of growth hormone (GH) and insulin-like growth factor (IGF)-I, which are known as both osmoregulatory and immunomodulatory hormones, were also examined in FW- and SW-acclimated fish. Compared with the intact gill arch of the same fish, the residuary filaments after biopsy showed significant reduction in Na+,K+-ATPase (NKA) and cystic fibrosis transmembrane conductance regulator (CFTR) mRNA levels in FW fish. In contrast, mRNA levels of these genes in the filaments with biopsy were increased in SW fish. Increased caspase gene transcription was observed in the cut filaments of SW fish, but not in those of FW fish. Lysozyme gene transcription was stimulated in the residuary gill filaments after biopsy in both FW and SW. Administration of salmon GH or IGF-I increased mRNA levels of NKA, CFTR, caspase, and lysozyme in the gills after biopsy in FW fish. In SW-acclimated fish, there was no significant effect of GH or IGF-I on the transcription of osmoregulatory or immune genes. The results in this study showed tight relationships between immunity, osmoregulation, and endocrine system in fish gills, and that nonlethal gill biopsy can be used for investigations of fish health.