SELECTION RESPONSE AND HERITABILITY ESTIMATES FOR GROWTH IN THE CHILEAN OYSTER OSTREA-CHILENSIS (PHILIPPI, 1845)

Oyster parent stock was taken from the 1987 natural spatfall of Ostrea chilensis collected on plastic plates in the Quempillen River Estuary of southern Chile. From the 40-month-old cohort 5,030 oysters were mo nitored for live weight and shell length. Divergent selection was carr ied out by applying a selection intensity of +/-1.755 for the trait '' live weight''. Five subgroups each of high selected oysters, low selec ted oysters and an unselected control group were conditioned in 15 150 -liter tanks. A highly significant correlation (r = 0.94, N = 5,030) w as found between the traits ''live weight'' and ''shell length''. Juve niles from the 10 selected and 5 control subgroups were individually t agged. Live weight and shell length were monitored after 8, 14 and 27 months in 200 oysters from each subgroup. The phenotypic serial correl ations for both traits indicate that either 8 or 14 months of age can be appropriate for the selection of parents to be used in an O. chilen sis breeding program. The ANOVA results show a significant difference, in both traits, between the high and low selected groups at 8, 14 and 27 months of age. The heritability estimates for increasing the trait ''live weight'' ranged between 0.43 +/- 0.18 and 0.69 +/- 0.11 while the heritability estimates for decreasing the same trait ranged betwee n 0.24 +/- 0.06 and 0.35 +/- 0.08. Mass selection appears to be a prom ising technique for the improvement of the Chilean oyster broodstocks.