Age at First Maturity and the Early Expression of Oocyte Recruitment Processes in Two Forms of Atlantic Salmon (Salmo salar)and Their Hybrids

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Abstract
The two pure lines and the reciprocal hybrids between an early maturing dwarf form of landlocked Atlantic salmon (Salmo salar) and a later maturing anadromous form were reared in captivity for a minimum period of 2.5 yr. Despite similar growth rates, 90% of female parr of the dwarf landlocked strain matured at age 2+ yr (fork length 15 cm), while no females of the anadromous form matured at this time. The weight of the ovary differed in the two pure forms at age 0+ and the numbers, size, and stages of previtellogenic oocytes also differed at age1+. Ovarian patterns of development and the time of onset of sexual maturation in the hybrid forms appeared intermediate to that of the parental forms. The implications of genetically controlled factors influencing rates of sexual maturation, growth, smoltification, and subsequent fecundity are discussed.