Osmoregulation and gene expression of Na+/K+ ATPase in families of Atlantic salmon (Salmo salar) smolts

This study reports that families of Atlantic salmon (Salmo salar) smolts vary in their ability to osmo- and iono-regulate following abrupt transfer to cold seawater. Eleven families of Atlantic salmon 0+ smolts were held in fresh water (2.4–4 °C) or transferred to seawater (1.9–4 °C) and sampled 0 h, 24 h, 96 h, and 30 days post-transfer. Plasma osmolality was significantly different among the families after 24 h of seawater exposure. The family with the lowest osmolality at 24 h also displayed the lowest plasma Cl– concentrations as well as the highest gill Na+/K+ ATPase activity. Gill mRNA expression of the Na+/K+ ATPase α1b isoform increased following seawater exposure, whereas the α1a isoform decreased, but there was no significant difference among families. Taken together, the interfamily differences in osmoregulatory ability are correlated with gill Na+/K+ ATPase activity but not the expression of two salinity-sensitive Na+/K+ ATPase isoforms. Furthermore, the data indicate that family differences in gill Na+/K+ ATPase activity were only apparent when assayed at the sampling temperature (4 °C) and not at a higher assay temperature (10 °C).