Reciprocal hybrids derived from Crassostrea gigas and C. angulata exhibit high heterosis in growth, survival and thermotolerance in northern China

Abstract The Pacific oyster is one of the most economically important species in global aquaculture. However, the production of C. gigas has been compromised by widespread and severe summer mortality events in recent years. To explore the possibility of obtaining a new hybrid line with rapid growth and high summer survival rate traits through hybridization, we performed a systematic comparative study on heterosis for growth and survival of C. gigas (GG), C. angulata (AA) and their reciprocal hybrids of C. gigas × C. angulata (GA) and C. angulata × C. gigas (AG) for 450 days in northern China. The fertilization and D-stage rates of reciprocal hybrids were lower than those of parental species, but obvious heterosis for growth, survival and metamorphosis were observed at larval stages. Meanwhile, the hybrid cohorts showed high heterosis for growth and survival at both juvenile and adult stages. Moreover, compared with growth, heterosis was higher in survival with a mid-parent heterosis ranged from 12.75% to 110.20% throughout the whole period. At day 450, the cumulative survival rate of hybrid GA increased by nearly 34% compared with GG, with a single patent heterosis I(GA/GG) of 191.14%. Notably, the final yield of hybrid crosses was significantly higher than that of parental lines, with a mid-parent heterosis of 182.72% and I(GA/GG) of 239.46%. To investigate the relationship between summer mortality and high temperature tolerance, the survivability of reciprocal hybrids and parental species through exposure to acute increasing temperature stresses for 96 h were compared. The reciprocal hybrids exhibited greater thermotolerance than the parental species, followed the order of GA > AG > AA > GG. Overall, our study confirmed that GA showed the greatest heterosis in terms of growth, survival and thermotolerance, which could be used as the preferred alternative variety in oyster farming in northern China.