Cycloheximide: Inhibition of Dermocystidium marinum in laboratory stocks of oysters.

Cycloheximide (acti-dione),an antifungal antibiotic, prolonged the life of oysters that were naturally infected with Dermocystidium marinum, a lethal fungus parasite. In closed aquaria, oysters treated with four concentrations (1, 5, 10 and 50 micrograms/ml/wk) of this antibiotic lived for several weeks to months longer than untreated control oysters. Presumably suppression of D. marinum infection by cycloheximide accounted for extended oyster longevity. The cycloheximide concentrations employed were chiefly inhibitory for lethal infections developed several weeks to months following cessation of treatment in all but one of the treated oyster groups. None of the oysters receiving 50 micrograms/ml/wk for 164 days showed D. marinum infections, by cultures, at death. The survival period of oysters treated for 45 days appeared directly related to antibiotic concentration. However, the survival period of those treated for 164 days was somewhat similar for all concentrations employed. Generally, oysters treated for 164 days lived longer and showed much fewer heavy infections at death than those treated for only 45 days. The feasibility of controlling D. marinum infections of oysters used for experimentation in closed systems by continuous treatment with a low level (1 %g/ml/wk) of cycloheximide is suggested by this study.