Genetic differentiation in the Chilean blue mussel Mytilus chilensis (Hupé 1854) was investigated based on the variation in the allozyme frequencies of Pgm, Gpi, Icd, Me, Gsr, Lap and Pep in eight samples collected along 1800 km from Arauco (VIII Region) to Punta Arenas (XII Region). Despite the large geographic separations, values of Neis unbiased genetic distance, D (0.004-0.048) and standardised genetic variation among populations, Fst (0.011-0.055) were small. The levels of gene flow (Nm = 8) found in this study prevent the effect of differentiation among populations by genetic drift. This findings indicate that its long-lived planktotrophic larvae provides this species with considerable dispersal ability throughout its range which is favoured by the ocean currents along the chilean coast. In terms of management of the M. chilensis fishery, the results provide no evidence for discrete stocks, with the possible exception of the Punta Arenas population. Considering the intensive aquaculture activities with this species the present study provide preliminary data which can be used as a baseline for further characterization and /or monitoring these mussel populations.

The oyster parental stock was taken from the 1998 natural spatfall from the wild population of Ostrea chilensis at the Quempillen River Estuary, located at Chiloe Island, southern Chile. From a cohort of 34 months of age 5232 oysters were monitored for the traits shell length and live weight. Selection was carried out applying a selection intensity of +1.7 for the trait live weight, using a control group. The conditioning was carried out in 5 tanks of 120 L, 3 of them containing high selected lines and other 2 control lines of oysters. A highly significant correlation (0.76, p<0.001, N=5232) was found between the traits live weight and shell length. Spat from the 3 selected subgroups and 2 control groups were obtained. Plastic collectors with the spat attached were placed in a common rearing tank. Shell length was monitored after 6 and 16 weeks of age in 200 juveniles of each selected and control lines. The ANDEVA results show a significant difference (p<0.05) between the shell length of the selected and control groups at 6 and 16 weeks of age. Also, a significant response to selection was obtained even when selection was applied for the trait live weight at 34 m-old. These results confirm those obtained in an earlier study using the same natural oyster population from Quempillén

La población base de Ostrea chilensis utilizada en el presente trabajo corresponde a una cohorte obtenida del estuario del río Quempillén, isla de Chiloé, sur de Chile. A los 34 meses de edad y en base a 5232 ostras de la cohorte tomadas al azar, se realizó una curva de distribución para los caracteres peso vivo y longitud de la valva. Como criterio de selección se aplicó una intensidad de selección de +1,7 para el peso vivo, manteniéndose un grupo control. Cada grupo, control y seleccionado (N=400 y N=600 respectivamente), se dividió al azar en subgrupos de 200 ostras, 3 de los cuales contenían líneas seleccionadas y los otros 2, ostras como grupo control. El acondicionamiento se realizó en 5 estanques de 120 L cada uno. El carácter peso vivo mostró tener una alta correlación fenotípica con el carácter longitud de la valva con un valor de 0,76 (N=5.232, p<0,001). Se obtuvieron juveniles en los 5 sub-grupos. Los colectores plásticos con los juveniles adheridos marcados se mantuvieron en crecimiento en un estanque común. Se realizaron dos monitoreos de crecimiento de longitud de valva en 200 juveniles tomados al azar en cada uno de los subgrupos seleccionados. El ANDEVA indica una diferencia significativa (p<0,05) en la longitud de la valva entre juveniles del grupo control y grupo seleccionado, a las 6 y 16 semanas de edad. Ello, aun cuando la selección se basó en el carácter peso vivo a los 34 meses de edad (talla comercial). Estos resultados confirman los obtenidos en un estudio previo utilizando la misma población natural de ostras de Quempillén