DIFFERENCES IN MITOCHONDRIAL 16S RIBOSOMAL GENE-SEQUENCES ALLOW DISCRIMINATION AMONG AMERICAN [CRASSOSTREA-VIRGINICA (GMELIN)] AND ASIAN [C-GIGAS (THUNBERG) C-ARIAKENSIS WAKIYA] OYSTER SPECIES

Limited field trials for potentially disease resistant Asian cupped oy sters were recently initiated in the central Atlantic coastal region o f North America. We have developed a simple and sensitive genetic assa y that unambiguously distinguishes the native Crassostrea virginica (G melin) from two of its exotic Asian congeners, C. gigas (Thunberg) and C. ariakensis (Wakiya). Homologous fragments (443 nt) of the mitochon drial rRNA large subunit were amplified from, and sequenced for, these three commercially important species of oysters. C. virginica exhibit s 85.5 and 84% sequence similarity to C. gigas and C. ariakensis (resp ectively) and contains seven additional nucleotides in the amplified 1 6S gene fragment. The two Asian species do not differ in gene length a nd display 95.1% sequence similarity. Numerous endonuclease restrictio n site differences are apparent among the three oyster species and we present a polymerase chain reaction/ restriction fragment length polym orphism strategy that can distinguish these species. This methodology will prove valuable in monitoring the ecological consequences, at all life history stages, of trial introductions of Asian Crassostrea speci es into this region.