Polyploidy induced in the American oyster, Crassostrea virginica, with cytochalasin B

Polyploidy was induced in the American oyster by treating the zygote with cytochalasin B. In treatments begun at 50 min after fertilization and lasting 20 min, 13 of 22 oysters treated with 0.1 mg/l cytochalasin and 3 of 4 treated with 1.0 mg/l were polyploid. In treatments with 0.5 mg/l, cytochalasin given from 0 to 15 min after fertilization resulted in 10 polyploids out of 20 and, from 15 to 30 min, 34 polyploids out of 46 examined. Juvenile oysters had about the same percentage of polyploid individuals as embryos. Only triploids were seen at 8 months, whereas triploids and tetraploids were observed in embryos. Oysters developed from treated zygotes set normally and subsequent survival was indistinguishable from those of controls. At 8 months the control and treated oysters both averaged 13 mm in shell height. Survival at 24 h was about 33% that of controls for the 0.1 mg/l treatment and 15% for the 1.0 mg/l treatment. Survival was greater for oysters treated for 15 min beginning immediately after fertilization than if treatment began later at 15 or 40 min.