SPATIAL VARIATION IN RESPONSE TO SELECTION FOR LIVE WEIGHT AND SHELL LENGTH FROM DATA ON INDIVIDUALLY TAGGED CHILEAN NATIVE OYSTERS (OSTREA-CHILENSIS PHILIPPI, 1845)

Divergent selection was carried out in Ostrea chilensis applying a sel ection intensity of +/- 1.755 for the trait 'live weight' at 40 months of age. Juveniles from the divergent selected and control groups were obtained, individually tagged and transferred to be grown in four mar iculture farms in southern Chile. Live weight and shell length were mo nitored after 14 and 27 months of age in oysters of each selected and control groups, A significant difference, in both traits, between the high and low selected groups at 14 and 27 months of age was found at a ll rearing sites, Both live weight and shell length showed significant correlated responses to selection for live weight at 40 months, incre asing and decreasing the traits under all growth environments. Most of the correlated responses did not vary among different locations. Howe ver, in all cases they varied significantly between the two stages of the oyster life cycle. Genotype-environment interactions were not appa rent for any trait, indicating that similar selection pressures will r esult in similar phenotypic changes for these traits across environmen ts. Mass selection appears to be a promising technique for improvement of Chilean oyster brood stocks.