To evaluate whether heterosis can be obtained from hybridization between Crassostrea gigas and C. ariakensis, a 2×2 factorial cross experiment was conducted between these two species in May 2010. Heterosis was first examined by comparing growth and survival of the two reciprocal hybrid crosses (GA and AG) with that of the two parental crosses (GG and AA). Gametic compatibility between the two species was asymmetric with GA crosses having higher fertilization success than AG crosses. In the hybrid crosses, GA offspring were significantly larger than AG offspring. Larval growth of interspecific crosses was similar to that of the maternal species during the first nine days, indicating dominant maternal effects. Beyond larval day 9, however, we observed asymmetry in single parent heterosis for growth and survival for both larvae and spat. GA crosses had good success in metamorphosis, while AG crosses produced only 72 spat. Heterosis was positive for GA hybrids but negative for AG hybrids, with the exception of higher AG survival during the grow-out stage. Maternal origin had a dominant effect on heterosis of both growth and survival, while the interaction between maternal origin and mating type was the second significant factor impacting growth heterosis during the first several days. After that, mating type emerged as an independent factor influencing growth heterosis for the rest of the larval stage. Genetic analysis confirmed that the spat of reciprocal crosses contained DNA from both species. Our study indicates that interspecific hybridization between female C. gigas and male C. ariakensis may be a promising method for genetic improvement of these two species for aquaculture.