Fishes of the Western North Atlantic 467 



(41°— 43°F). In another hatchery experiment, hatching occurred much sooner at 42° F 

 (88 days) than at 33° (191 days). 



Names Applied to the Successive Life Stages. The Atlantic Salmon at various stae;es 

 of growth has been given the following distinctive names: 



Alevin: the stage from hatching to absorption of the yolk sac, which occurs at a 

 length of about one inch; often called the yolk-sac stage. 



Fry: the stage between absorption of the yolk sac and acquisition of the parr marks. 



Parr: the young stage spent entirely in fresh water when it has 8-1 1 or 12 dark 

 vertical bars or parr marks on each side, acquired soon after the disappearance of 

 the yolk sac. Some male parr mature during this stage but the females do not, so far 

 as is known. 



Fingerling: same as parr. 



Smolt: a young fish that has acquired a coat of guanine that hides its parr 

 marks and gives it a shiny, silvery appearance. This change usually occurs after the 

 fish has spent one to four years, and exceptionally as much as seven years, in the 

 natal river. Following this transformation the young Atlantic Salmon migrates to the 

 sea (pp. 468-470). 



Grilse: a mature fish that returns to fresh water to spawn after one complete 

 year at sea; distinguishable from the older fish by its more deeply forked caudal fin 

 and its smaller size; its average length in Canada is 18—24 inches, its weight 3-5 

 pounds, with extreme ranges of 2 — 14 pounds reported. 



Salmon : a mature fish that has spent two or more years in the sea before returning 

 to fresh water to spawn for the first time; its weight with two years of sea-life, 6.5-16 

 pounds (usually 10-12 lbs.), and with three years, 20-35 pounds or more; most of 

 the large fish, 40-50 pounds, are females that have been at sea a long time and have 

 spawned only once or not at all. 



Kelt: a thin adult that has spawned and still shows the dark color assumed 

 during its freshwater stay; often called a black salmon. 



Mended Kelt: a fish that has recovered from the kelt period by regaining its 

 silvery color and a more normal plump form. 



The Alevin Stage. The newborn alevin, 15—20 mm long, are hatched with a mass 

 of yolk which nourishes them but which also weighs them down and keeps them from 

 maneuvering freely; during this time they usually remain on the river bed. The yolk-sac 

 period for hatchery-reared alevin varies between 29—65 days (usually 39-53 days), with 

 temperature the controlling factor; as in the hatching of the eggs, the higher the temper- 

 ature the shorter the yolk-sac period (x6). Vibert's studies (rjj) have confirmed earlier 

 conclusions that alevin hatched under gravel are hardier than those reared in a hatchery, 

 are better developed, and average 1 5 "/o heavier. With the disappearance of the yolk, the 

 little Salmon must begin to seek their own food. They are then gregarious {jS), resting 

 on the stream bed with others and rising to take prey, either individually or with a group. 



From Parr to Smolt. Soon after the disappearance of the yolk, which marks the end 

 of the alevin stage, the young fish develop the characteristic crossbars along each side 



30 • 



