FACTORIAL CROSSING OF 5 GEOGRAPHICALLY IS OLATED POPULATIONS OF THE NATIVE CHILEAN OYSTER (OSTREA-CHILENSIS PHILIPPI 1845)

The present study reports on pure matings and crosses of five geograph ically isolated populations of the Chilean oyster, Ostrea chilensis (P hilippi 1845). Oysters were raised in suspended culture in five aquacu lture farms in Chiloe Island, southern Chile, in order to evaluate het erosis and the genotype-environment interaction on economically import ant animal production traits. A random sample of one- hundred fifty ad ult oysters was obtained from each population. Pure lines and crosses between populations using the pair-mating design were carried out at t he Quempillen Hatchery, Ancud. After 24 months of growth, substantial crossbred advantages and population differences were observed in the s hell length and live weight traits. With regards to the localities stu died, an initial gain of 41.5% in ''shell length'' and 59.7% in ''live weight'' was achieved by using the Linao bay instead of the Quempille n estuary (genotype-environment interaction). Significant deviations f rom the mean parental population (heterosis) were observed in over hal f (26 out of 45) of the comparisons between crossbreds and parental li nes. The highest percentage of heterosis was found in the cross betwee n the Pullinque and Rilan populations (44.6%) cultured in Quempillen e stuary. These results point to the presence of non-additive gene effec ts (dominance) on both traits but do not imply that crossbreeding is g uaranteed.