1Tamano Station, National Center for Stock Enhancement, Fisheries Research Agency, Tamano, Okayama 706-0002, 2Yaeyama Station, National Center for Stock Enhancement, Fisheries Research Agency, Ishigaki, Okinawa 907-0451, Japan
We described the relationship between the mass mortality of megalops and the morphogenesis of zoeas in the seed production of the swimming crab Portunus trituberculatus. The survival rate of larvae from the last (fourth) zoeal stage to the first crab stage was lower than that from the first to fourth zoeal stage. Survival rate tended to decrease with increasing frequency of abnormal molting during the metamorphosis to megalops. The relationship between the frequency of abnormal molting and the relative chela length to carapace length in the fourth zoeal stage showed a significant positive correlation. Thus, it was revealed that the morphologically advanced fourth stage zoeas were unable to undergo normal metamorphosis to megalops and larval mass mortality occurred.