INDUCTION OF TETRAPLOIDY IN MUSSELS BY SUPPRESSION OF POLAR BODY FORMATION

Fertilized eggs of the mussel Mytilus galloprovincialis were exposed t o cytochalasin B (CB, 1 mg/l) from 7 until 35 minutes after inseminati on to inhibit both polar body I and II formation. Cytological observat ions revealed that many of the CB-treated eggs contained five pronucle i. DNA microfluorometry of trochophore larvae from CB-treated eggs ind icated ploidy levels from diploid to decaploid, with 18% classified as tetraploid and 12.4% as pentaploid. Survival from the trochophore sta ge to day 20 was 8.2% for the CB group compared to 48.8% for the contr ol group. One month after initial settlement, DNA microfluorometric an alysis of 29 individual spat from the CB group showed that 24.1, 58.7, and 17.2% were diploid, triploid, and tetraploid, respectively. Previ ously, induced tetraploidy has only been found in embryos and larvae. The discovery of tetraploid spat indicates a potential for tetraploid bivalve production.