Influence of Parental Smolt Age and Sea Age on Growth and Smolting of Hatchery-Reared Atlantic Salmon (Salmo salar)

Abstract

Hatchery-reared Atlantic salmon, Salmo salar, consistently developed bimodal length–frequency distributions by the first November following hatch. In a study of 32 hatchery populations involving two year-classes, mean length in the lower mode showed little variation among populations and was not correlated with either the smolt age or sea age at first maturity of their parents. Mean length and the proportion of individuals in the upper mode were both variable among populations and correlated with parental age variables. Large mean length in the upper mode was strongly associated with early smolting male parents and late maturing female parents. The proportion of individuals in the upper mode was more strongly correlated with the age variables of the female parent. Late smolting and early maturing female parents tended to produce relatively greater proportions of fish in the upper mode. The optimum growth rate which produced the greatest proportion of individuals in the upper mode occurred when 8–15% of the total population matured precociously as parr. A threshold size hypothesis for precocious maturation is discussed.Key words: Atlantic salmon, genetics, growth, bimodality, precocious sexual maturation, smoltification