Heterosis in Growth and Survival of Intraspecific Crosses Between Different Shell Color Strains in the Wild Population of Manila Clam (Ruditapes philippinarum)

To develop Manila clam (Ruditapes philippinarum) varieties suitable for cultivation in northern China, we conducted a 2×2 complete diallel cross between the Dalian wild orange clam strain (designated as O) and the white clam strain (designated as W). Initially, two diallel cross groups—O♀×W♂ (OW), and W♀×O♂ (WO)—along with two inbred groups—O♀×O♂ (OO), and W♀×W♂ (WW)—were established. Growth and survival during the larval and juvenile stages were evaluated; hybrid and inbred groups were compared to identify potential heterosis. The crossed groups exhibited a markedly higher fertilization rate compared with the inbred groups (P<0.05), while the hatching rates did not exhibit any statistically significant variations. The larvae showed distinct differences in growth performance across combinations on days 6, 12, and 15 post-hatching, with the OW group demonstrating the greatest survival rate (P<0.05). The juveniles of the OW and WO groups exhibited significant growth advantages on days 30, 60, 90, and 120, while the OO group showed the lowest survival rate. After 120 d of age, the shell colors in the OW, WO, OO, and WW groups were mainly characterized as orange–white, white–orange, orange, and white (with a dark stripe on the dorsal side of the left shell), respectively. These findings suggest that this cross combination possesses considerable breeding potential and offers an effective breeding-based approach for enhancing the genetic traits of R. philippinarum.