Heterosis and combining ability of reciprocal hybrids between “Haida No.1” strain and orange shell line of the Pacific oyster (Crassostrea gigas)

The Pacific oyster (Crassostrea gigas) which originated from East Asia, has been a dominant commercial species in northern China. However, frequent mass mortality during summer in farming areas has severely restricted the development of oyster aquaculture. In order to develop a new strain of C. gigas with the traits of fast growth and high survival rate, intra-specific hybridization was carried out using the “Haida No. 1” strain (H) and orange shell strain (O), which were successively mass selected for 11 and 8 generations, respectively. The heterosis for growth and survival as well as general combining ability (GCA) and specific combining ability (SCA) were assessed for two purebred groups HH H(♀)×H(♂) and OO O(♀)×O(♂) and two reciprocal hybrids HO H(♀)×O(♂) and OH O(♀)×H(♂). On day 20, the mid-parent heterosis (M_F1) for survival of hybrid groups was 58.03%. Compared to HH groups, the survival rate of HO and OH increased by 31.48% and 35.80%, respectively. On day 360, the growth among four groups followed the order OH>HO>HH>OO, the M_F1 for shell height and living weight of reciprocal hybrids were 24.65% and 46.02%, respectively. Compared to HH groups, the shell height and living weight of OH group on day 360 increased by 23.51% and 39.60%, respectively. Two hybrid groups also exhibited high heterosis in survival, with mid-parent heterosis M_F1 and high-parent heterosis H_HO, H_OH at 68.31%, 40.29% and 53.96%, respectively. As male parent, the “Haida No.1” strain exhibited negative value for general combining ability in survival on day 180. However, the general combining ability was positive when the “Haida No.1” strain was employed as parent at other stages, which indicated the “Haida No.1” strain can be chosen as an excellent parental strain for crossbreeding with other strains of C. gigas. The values of special combining ability for growth and survival of OH group were higher than those of HO group. This suggested the progeny with higher heterosis could be obtained by using the “Haida No.1” strain as male parent and orange shell strain as female parent.