| Summary: | This thesis studies the variability of several Atlantic salmon (Salmo salar) reproductive traits, with a particular emphasis on the sea age at first maturity, a trait of foremost importance for both management of natural stocks and commercial salmon aquaculture. Three groups of salmon, belonging to several families were followed from spawning to grilse maturation. A combination of cold-branding and jet-injection of Aldan Blue in several fin locations proved to be satisfactory to identify fish at the individual and family levels and has allowed the compilation of precise growth and maturation history for each fish. A considerable diversity of maturation patterns was observed among individual fish, as well as important variation among families in maturation rates. A complex pattern of interactions between growth and maturation was evidenced. A model of maturation "triggering" is proposed to explain these observations: a fish appears to initiate maturation if its level of energy stores in spring is above a sex specific threshold level. For fish having the same previous maturation history, the level of energy store in spring appears mostly dependent on the fish growth over the winter, and to a lesser extent on the level of energy stores at the beginning of the winter. Differences among families for rate of maturation appear to be mostly due to differences among families for the relative allocation of surplus energy into somatic growth versus energy stores maintenance, and to a lesser extent to differences among families for winter growth capabilities. Some practical considerations about genetic and environmental manipulation of maturation in the aquaculture context are discussed.
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