Landlocked salmon derived from a wild population of stunted ouananiche and bred in the laboratory showed signs of smoltification, but adaptation to sea water was slow and limited to 11% of the fish tested. Sea water survival was not related to initial size, within the range used, nor to sex, age (2 + yearsv. 3 + years) or spawning history.Freshwater ouananiche had fewer gill chloride cells than anadromous smolts of similar size in fresh water. Anadromous smolts showed an increase in chloride cells after adaptation to sea water and those ouananiche which successfully adapted to sea water had a greatly increased number of gill chloride cells.