SELECTION EXPERIMENTS IN SALMON RANCHING .1. GENETIC AND ENVIRONMENTAL SOURCES OF VARIATION IN SURVIVAL AND GROWTH IN FRESH-WATER

A research program in salmon ranching in Iceland was started in 1987. The primary aim was to study genetic variation in return frequency to the site of release of smolts. Results from the freshwater period are presented. Broodstock of Atlantic salmon (Salmo salar) were taken from five stocks in Iceland in 1987 and 1988. Families were made by using semen from one male to fertilize eggs from three females. After fertilization, the eggs from each family were reared in separate egg trays. At startfeeding, each family was reared in separate tanks, using a total of 298 families. Survival was recorded for each family from eyed-egg stage until 12 weeks after startfeeding. Individual weight and length was recorded on a sample of fish from each family 190 days from the beginning of the startfeeding period. Significant differences (P < 0.05) between stocks were found for survival, length and weight for both yearclasses. Significant phenotypic correlations between egg size and the traits survival, weight and length were estimated to be 0.23, 0.23 and 0.22, respectively. The estimates of heritabilities calculated based on sire components from the total material were 0.04 for survival, 0.16 weight, and 0.10 for length when weight and length were adjusted for egg size and number of fish per tank. Heritability estimates using dam components were 0.34 for survival, 0.36 for weight and 0.39 for length. The genetic correlation between survival and weight estimated from the total material was 0.31 +/- 0.26, and between survival and length 0.39 +/- 0.26. Finally, the genetic correlation between weight and length was estimated at 0.98 +/- 0.01.