Abstract
Transfer into sea water produced an immediate and marked depression of the cruising speed of chum salmon fry. Despite considerable recovery from this initial effect the fish exhibited a continuing slight depression of cruising speed over the entire experimental period (80 hours). Variations in total body levels of chloride and water were significantly correlated with changes in cruising speed, suggesting that variations in activity might be related to the process of osmoregulatory adaptation to sea water. Possible mechanisms underlying this effect have been discussed.