Gill Na +–K +-ATPase activity and hypoosmoregulatory ability of seaward migrating smolts of anadromous Atlantic salmon ( Salmo salar), sea trout ( Salmo trutta) and Arctic char ( Salvelinus alpinus) in the Hals river, northern Norway

Abstract

Gill Na +–K +-ATPase activity and hypoosmoregulatory ability of seaward migrating smolts of anadromous Atlantic salmon, sea trout and Arctic char were compared in a river system where all three species co-exist. Migrating Atlantic salmon and Arctic char were of similar size (mean lengths 13.3 and 14.6 cm, respectively) whereas the trout smolts were significantly larger (mean length 19.1 cm). The char smolts had the lowest condition factor and the trout smolts the highest. Migrating smolts of all three species had similar high gill Na +–K +-ATPase activity. The mean plasma Cl − concentrations after 24 h in seawater were not significantly different between Atlantic salmon and sea trout (about 150 and 160 mM, respectively), whereas these of Arctic char had significantly higher mean concentrations (about 180 mM). Smolts of both Atlantic salmon and sea trout in river Halselva in northern Norway were pre-adapted to seawater, perhaps the salmon smolts somewhat better despite their smaller body size. The small-size, first-time migrants of the Arctic char were not pre-adapted to life in full-strength seawater.