GROWTH AND EARLY SEXUAL-MATURATION IN BALTIC SALMON (SALMO-SALAR) PARR

The relationship between sexual maturation and growth in Baltic salmon (Salmo salar) parr was studied in hatchery stock originating from the Umealven (Ume River) in northern Sweden. The probability that a male parr would mature sexually at age 1 + was positively related to its size at the start of the experiment at age 0 +. The specific growth rate and condition factor of maturing and nonmaturing males were similar until the onset of gonadal growth, when the growth rate of maturing males decreased. Sibling groups of immature parr were fed different rations during the 3 weeks prior to the start of gonadal development. The incidence of sexual maturation in the groups given different rations was linearly related to the growth rate during the period of different feeding rates. This study suggests that both the size at age 1, resulting from the growth rate during the first summer, and the opportunity for growth during the period preceding the onset of gonadal growth affect the incidence of maturation in male parr of age 1 +.