THE EVOLUTION OF THE FRESHWATER RACES （淡水种族的进化）.pdf

THE EVOLUTION OFTHE FRESHWATER RACES OFTHE ATLANTIC SALMON (SALMO S.ALAR L) INEASTERNNORTH AMERICA G. Power* HE life cycle of the Atlantic salmon (Salmo salar L.) is typically divided T betweenfreshwaterandmarine environments. Spawning occurs in rivers and the juvenile salmon, known as parr, remain in this habitat for from 1 to 7 years before changing into smolts and migrating to the sea. Little is known of themarine life of the salmon except thatit usually occupies a period of from 1 to 3 years, during which growth is extremely rapid. Following this phase the fish return to the rivers of their origin, attain fullsexualmaturity,and spawn, thus completing the cycle. All Atlantic salmondo not conform to this pattern, however, and a number of forms, known as Ouananiche, Sebago salmon, landlocked salmon, etc., are recognized, which complete their life cycle entirely’in fresh water. These freshwater races are exceedingly widespread in eastern North Amer- ica. Jordan and Evermann (1896) recognized two types and, although they were indistinguishable morphologically, listed them as subspecies of the Atlantic salmon, Salmo salar sebago and Salmo salar ouananiche. Wilder (1947) was unable to find any morphological criterion for separating the Sebagosalmon from theAtlantic salmon. The mostobviousdistinction between theAtlantic salmon and its freshwater races is thatthelatter do not migrate to sea at any stage in the life cycle, although in many in- stances they are not prevented from doing so by other than physiological barriers. Sebago salmon inhabit lakes that are