RESPONSES OF JUVENILE CHUM, PINK, AND COHO SALMON TO SHARP SEA-WATER GRADIENTS

Abstract

The responses of chum, Oncorhynchus keta (Walbaum), and pink, O. gorbuscha (Walbaum), salmon fry, and coho, O. kisutch (Walbaum), salmon fry and smolts to sea water were studied in sharp-gradient tanks. Chum and pink fry responded positively to isotonic and hypertonic solutions of sea water, but coho fry only to the former. During parr–smolt transformation, coho responded positively to hypertonic sea water. Responses of chum fry acclimated to sea water for 24 hours prior to observation were comparable in intensity to those of unacclimated fry, but less rapid. Activity of acclimated fry decreased less rapidly than did that of unacclimated fry. Fresh water control experiments indicated the presence of some factor or factors which resulted in preferences for "recognized" areas. The effects of positive responses to increased salinity are discussed in relation to the migratory movement of these species from fresh water into the sea.