The effects of hypophysectomy, prolactin therapy and environmental calcium on freshwater survival and salinity tolerance in the brown trout <i>Salmo trutta</i> L.

Abstract

Hypophysectomy resulted in a loss of ability of the euryhaline salmonid, Salmo trutta to survive in fresh water. The mean survival time was 4–5 days. Maintenance in a medium containing 5 mM calcium increased the mean survival time to 8 days while 10 mM decreased it. Injection of 0–21.U./gm prolactin enabled hypophysectomized fish to survive the 2‐week duration of the experiment. High environmental calcium, or pre‐adaptation to a medium of high calcium, increased salinity tolerance of the brown trout probably by promoting a quick return of plasma electrolyte concentration to normal after transfer to sea water.