Smolting of Hatchery-Reared Steelhead Transferred as Eyed Eggs from the Northern to the Southern Hemisphere

Abstract The effects of a Northern-to-Southern Hemisphere shift on the growth and smolting of steelhead (Oncorhynchus mykiss) were monitored by reference to physiological criteria. Eyed eggs were imported from the Alsea River Trout Hatchery, Oregon, USA (latitude 44°N), to the Lake Rupanco Experimental Hatchery in Chile (latitude 41°S). This transfer of eggs resulted in a notable variation in the age and size at which fish smolted. A minimum smolting size of about 10 cm was observed in the first southern spring of life, when fish were 7–8 months old. Fish that did not reach this size smolted in the second spring of life at age 20 months. Based on our current understanding of the effects of environmental variations on smolt physiology, we offer guidelines for increasing the efficiency of smolt production for this anadromous salmonid in the Southern Hemisphere.