Acute toxicity of formaldehyde to the pearl oyster Pinctada fucata martensii

The acute toxicities of formaldehyde to one- and two-year-old pearl oysters, Pinctada fucata martensii, were determined under a semi-static condition at 20 and 25°C. The median lethal concentration (LC50) lowered progressively as the duration of exposure increased. The toxicity curves became almost asymptotic with the time axis by 96 h. The 96 h-LC50 was 7.7 mg/l at 20°C and 5.3 mg/l at 25°C for the one-year-old pearl oyster. It was 10.2 mg/l at 20°C and 6.4 mg/l at 25°C for the two-year-old pearl oyster. Variations of the dissolved oxygen concentration and the formaldehyde concentration in the test solutions imply that pearl oyster can defend themselves from toxic effects of formaldehyde by reducing their respiration rate. Furthermore, pearl oysters are capable of lowering the formaldehyde concentration in surrounding water, thus defending themselves.