Data recorded on the 1986 year-clas

Data recorded on the 1986 year-class of Atlantic salmon in the Norwegian national
breeding program were analysed (Material I). This year-class was hatched in January
1986 at AKVAFORSK’s combined research and breeding centre at Sunndalsora,
Norway and reared in the same facilities during the freshwater period. The breeding
program stock had been reproduced in captivity for four generations and selected for
increased growth rate and reduced percentage of early maturation (Refstie, 1990). A
total of 44 sires and 119 dams were used as breeders to produce this year-class. Each
full-sib group was hatched in a separate tray and reared in separate I m2 indoor
fibreglass tanks until they were large enough to be tagged by fin-clipping and freezebranding
and communally stocked. During the freshwater period the fish were vaccinated by the immersion method against vibriosis (V. anguillarum) with a commercial
vaccine. At about 18 months of age (post hatch), 200 fish from each full-sib group were
transferred to sea water and reared for another 2 years in net cages at AKVAFORSK’s
breeding centre at Averoy. The data for these fish used in the present investigation
included the occurrence of early maturation after 1 year in seal water, and slaughter
weight and survival recorded at slaughter after 2 years in sea water.