LAUSR

Abstract Pacific oyster Crassostrea gigas is one of the most important global aquaculture bivalve species, and its growth traits have been improved by heterosis in the progeny produced by hybridization. However, comprehension of the molecular mechanisms implicat-ed in heterosis still remains elusive. In this study, a diallel cross between a selected line “Haida No. 1” and an orange-shell line of C. gigas was generated. The mid-parent heterosis and best-parent heterosis analysis on growth traits, including shell height, shell length, shell width and total weight, showed that the hybrid crosses exhibited a growth heterosis relative to the parental crosses. And the fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) revealed that the total DNA methylation level was significantly lower in hybrid crosses than in parental crosses, and the total methylation level was negatively associated with growth traits. Moreover, the mRNA expression level of DNA methyltransferases gene 3 (Dnmt3) of C. gigas was significantly different among four populations, which was also positively correlated to the total DNA methylation level. This work firstly provided clues for correlations between the heterosis of growth traits, total DNA methylation level and Dnmt3 mRNA expression and will facilitate the understanding of heterosis formation in the oyster.