| Summary: | Post-smolt growth rate and age at first maturation are compared for sib groups or population groups of salmon originating from Norwegian rivers and fish farms. Generally, high correlations were found between corresponding values (lengths at different ages and proportions of mature fish in the second and third sea years) for one and two year-old smolt. One year-old smolts were smaller than the two-year olds at the smolt stage and grew slower during their first sea year, but the two categories reached practically the same total length after two years in the sea. In most groups, and in the total material, one year-old smolts gave higher proportions of grilse. Proportions of mature fish during their third sea year were similar for one and two year-old smolt of the same groups. Pronounced variations between sib groups and population groups were found both in growth rate and mean age at first maturation. This variation was much bigger than the variation between one and two year-old smolts of the same sib group.
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