ABStract
Of the numerous reports of hybridization attempts in the genus Crassostrea, none has been confirmed genetically. Three replicates of a 2x2 factorial mating of Crassostrea gigas X C. rivularis (C.
arakiensis) were produced to examine the viabiliry ofthis cross. Fertiiization rate, yield of48-b-old
larvae. and survival of fertilized eggs was lower in the hybrids than pure crosses. All crosses showed
similar larval growth rates, except C. rivularisxC. grgas, which grew more slowly. Cenetic control of
eyed larral size was indicated by the intermediate size ofhybrids compared io pure crosses. Spat were
obtained lrom most cultures'and were shown by protein electrophoresis to be hybrids. Contaminants
were also present, underscoring the need for genetic confirmation in studies on bival ve hybridization.