INTRODUCTION.
There are numerous reports on attempted inter specific hybridization in the
genus Crassostrea, including several between C. gigas and C. rivularis (C.
arakiensis) (Gaffney and Allen, 1993 ). Surprisingly these reports of hybridization
were not verified genetically. Genetic confirmation is essential because
of the possibility of contamination by larvae from other broods held
Contemporaneously in the hatchery. We showed such contamination in a hybrid
culture of C. virginicax C.glgas (Allen et al., I 993 ) and have discovered
it to be the probable source of putative hybrids from other laboratories (Gaffney
and Allen, unpublished data, 1992).