Studies of interspecific backcross between hybrids of (Crassostrea angulata ♀ × C. gigas ♂) and their two parental species

Abstract

Interspecific hybridization between oysters Crassostrea angulata and C. gigas has been recently studied, but it remains unclear how these hybrids can be used to advance the techniques of oyster farming. Interspecific backcrossing is expected to transfer the favorable traits of a species to genetically altered F1 hybrids. In this study, therefore, interspecific backcrosses were conducted between the hybrids of C. angulata ♀ × C. gigas ♂ and their parental species, which included nine groups based on their crossed combinations: hybrid combinations and self-breeding (AG GA, GG and AA); backcross combinations (HA, HG, AH and GH); hybrid self-breeding (HH). Results showed high cleavage rate and D-larval rate in each group without fertilization barrier. Among groups, we observed (1) the highest shell height of AG on Day 12, (2) faster growth of AH than other groups from Day 90 to Day 180, (3) the highest shell height of AG after Day 180. Limited superiority of the backcross groups was found on Day 360, but the degree of heterosis of AG and AH was higher than that of other groups. A mild degree of outbreeding depression in terms of growth was found in self-breeding progenies. The survival rate among groups follows an order: the group with C. angulata as Dam > the group with the hybrid as Dam > the group with C. gigas as Dam. Positive outbreeding depression in terms of survival rate was observed on Day 360. In particular, the survival rate of AH was higher than that of other groups with a heterosis value of 54.80% at the harvest stage. In terms of relative yield, outbreeding depression and inconspicuous superiority were found. Overall, hybrid combination AG exhibited the best performance among groups, followed by backcross combination AH.