| Summary: | I tested the hypothesis that families of Atlantic salmon vary in their ability to osmoregulate in seawater under cold conditions. Eleven families of Atlantic salmon 0+ smolts were transferred to seawater and sampled 0 h, 24 h, 96 h, and 30 days post transfer. Plasma osmolality levels were significantly different between the families at 24 h of seawater exposure. The family with the lowest osmolality also displayed the highest gill Na+, K+ ATPase activity. Gill mRNA expression of Na+, K+ ATPase [alpha]-subunit isoform [alpha]1b increased following seawater exposure, whereas the [alpha]1a isoform immediately decreased, but there was no significant difference between families. Taken together, the inter-family differences in osmoregulatory ability suggest a genetic basis for salinity tolerance in Atlantic salmon smolts. Furthermore, it appears that under cold conditions (4°C) gill Na+, K+ ATPase plays an important role in ion regulation.
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