A NOVEL METHOD TO PRODUCE TRIPLOIDS IN BIVALVE MOLLUSKS BY THE USE OF6-DIMETHYLAMINOPURINE

To date, pressure shock, heat shock, and chemical treatment with cytoc halasin B have been the major methods used to induce triploid bivalves . In this study, triploid bivalves were induced by a new chemical trea tment using 6-dimethylaminopurine (6-DMAP). The capacity of 6-DMAP to produce triploid eggs and larvae was investigated in the Pacific oyste r, Crassostrea gigas, the giant sea scallop, Placopecten magellanicus, and the blue mussel, Mytilus edulis. The triploid yields from the 6-D MAP treatments were compared with those of cytochalasin treatments. Th e highest percentage of triploid production was 90% in the Pacific oys ters when the fertilized eggs were treated for 20 min with 300 muM 6-D MAP at 15 min after fertilization and 95% in the giant scallops when t reated for 15 min with 400 muM 6-DMAP at 70 min after fertilization. I ncreasing durations of 6-DMAP treatments improved the efficiency of tr iploid induction. However, long incubations with 6-DMAP, which overlap ped the period of first mitotic cleavage, led to the development of ab normal larvae. These included low percentages of normal veliger larvae in the Pacific oysters and developmental arrest at the trochophore st age in the blue mussels. The percentage of abnormalities increased wit h increased treatment duration. Triploid larvae of Pacific oysters pro duced by 6-DMAP or cytochalasin treatments had equivalent growth rates and were similar to those of control diploid larvae. However, triploi d larvae showed high mortalities following these two chemical treatmen ts. Overall, the results clearly demonstrate that 6-DMAP was an effici ent and practical inducer of triploidy in bivalve molluscs. Moreover, the described procedure is the most simple and reproducible method eve r reported. In addition, 6-DMAP is safer to handle than cytochalasin w hich is classified as a carcinogen.