Acute Mortality of Soft Shell Clam, Mya arenaria, Larvae, Green Sea Urchin Strongylocentrotus droenbachiensis, Larvae, and Rotifers, Brachionus plicatilis, Exposed to Cypermethrin (Excis ™)

ABSTRACT

The acute effects of Cypermethrin (Excis (tm)) on soft shell clam, Mya arenaria, larvae, green sea urchin, Strongylocentrotus droenbachiensis, larvae, and rotifers, Brachionus plicatilis, were studied in the laboratory. Cypermethrin (Excis(tm)) is used at a concentration of 5 μg/L as a bath treatment of salmonids against sea lice, predominantly, Lepeophtheirus salmonis. Zooplankton were exposed for 1, 6, and 12 hours to different concentrations of Cypermethrin, at water salinity levels of 32 (±0.6) ppt and a temperature of 12° C. Clams, urchins, and rotifers were exposed to Cypermethrin concentrations of 0, 0.005, 0.05, 0.5, 5.0, 50, 500, 5,000, and 50,000 μg/L. These concentrations correspond to 0,1/1000,1/100,1/10,1,10,100,1,000, and 10,000 times the manufacturer's recommended treatment concentration.

Only at concentrations of between 10-10 000 times greater than the recommended treatment dose of 5 μg/L, did Cypermethrin treatment cause statistically significant mortality in the clam larvae (P < 0.05), sea urchin larvae (P < 0.05) and rotifers (P < 0.05). The LC50 values for soft shell clam larvae mortality after 1, 6 and 12 hours of exposure were calculated at 13,490; 11,749; and 10,715 μg/L, respectively. For the sea urchin larvae the LC50 values after exposure for 1, 6, and 12 hour treatment durations were 21,5207; 39,716; and 16,982 μg/L, respectively. All LC50 values for the rotifer were > 50,000 μg/L.

Soft shell clam larvae, green sea urchin larvae, and rotifers are not significantly affected by exposure to Cypermethrin concentrations below the manufacturer's recommended treatment dose.

Key Words:

• Mortality
• larvae
• clam
• sea urchin
• rotifers
• Cyperme-thrin