Selection Response for Growth Rate (Shell Height and Live Weight) in the Chilean Blue Mussel (Mytilus Chilensis Hupe 1854)‪.‬

ABSTRACT The parental stock was taken from the 1999 natural spatfall of Mytilus chilensis collected in the Yaldad Bay of southern Chile. From the 22-mo-old cohort 5,688 mussels were monitored for live weight and shell length. Selection was carried out by applying a selection intensity of 1.755 for the trait "live weight". Five selected lines and five lines of an unselected control group were conditioned in seven 150-L tanks. Juveniles from the 3 selected and 2 control lines were individually tagged and transferred to three geographically distant mussel farms in southern Chile. Live weight and shell length were monitored after 10, 14, 18, and 22 month of age in all experimental mussels. The ANOVA results showed a significant difference, in both waits, between the selected and control groups at every age and location. Realized heritabilities for the trait "live weight" ranged between [h.sup.2] = 0.35 and [h.sup.2] = 0.54, whereas those for the trait "shell height" ranged between [h.sup.2] = 0.32 and [h.sup.2] = 0.49. Genotype-environment interactions were not apparent for either trait, indicating that similar selection pressures result in similar phenotypic changes for these traits across environments. These results suggest that mass selection for the improvement of the traits live weight and shell height would be effective in the Chilean mussel broodstocks. KEY WORDS: mussel, Mytilus ehilensis, selection response, growth, Chile