Selective breeding and crossbreeding are seen widely in genetic improvement of crops as well as molluscs. In this study, we constructed complete 4×4 diallel crosses using broodstock from 4 geographical subpopulations of sea scallops along the Atlantic coast of Canada, and heterosis and combining abilities in growth and survival rates at larval and adult grow-out stages were analyzed. The results indicated that variable heterosis in growth and survival exist in larval and adult stages. In many cases, the fitness traits increased with general combining abilities, especially at the larval stage, but in some cases, groups with high growth or survival rate but low general combining abilities were also observed. Reciprocal effects and maternal reciprocal effects were observed in growth and survival at the larval stage and also in adult growth. Two hybrid strains with superior growth and survival traits over purebred and other hybrid groups were selected that can be used in future culture practice.