Growth Rate and Survival in Pure Population Matings and Crosses of the Oyster Crassostrea virginica

Phenotypic differences were observed among pure population matings and crosses grown in two natural environments for the following characters: larval shell length, juvenile and adult shell length, weight, and survival at different times. For growth characters, the phenotypic variability between locations was greater than the variability among genetic groups within locations; however, the magnitude of the differences depended on the locality. The crosses exhibited higher survival than pure population matings, and locality had no effect on survival. In growth and survival, some crosses deviated positively from the mean of the parental populations. This may be a manifestation of heterosis. The genetic enhancement of commercially important characters in shellfish will eventually require the formation of a closed breeding unit with a broad genetic base for domestication and selection. It is recommended that an evaluation of natural populations as outlined in this study is a necessary prerequisite to achieve this objective.