ABSTRACT
The delicate silvery fish, the smolts, which migrate seawards each spring were thought by early naturalists to be a distinct species from the drab, brownish parr in the freshwater reaches of rivers, until it was demonstrated that both were juvenile forms of the anadromous salmon and trout. Several reports of a fall in total body lipid and a reciprocal rise in body water content in smolting Atlantic salmon have been made. Juvenile salmon parr adopt and defend bottom-feeding territories, showing a preference for boulder-strewn sections of the river bed with a fast flow of water. Several authors have reported a seasonal rise in the salinity preference exhibited by the Pacific salmon during or preceding smoltification. An understanding of the physiology of smoltification is beneficial to manipulating and monitoring the process under hatchery conditions, and to timing saltwater transfer or release of smolts.
