Acute toxicity of emamectin benzoate (SLICE(trade mark)) in fish feed to American lobster, Homarus americanus

SLICE(trade mark) (active ingredient 0.2% emamectin benzoate (EMB)), a feed premix developed by Schering-Plough Animal Health for the control of sea lice on cultured salmonids, is registered for use in several countries and is being prescribed on an emergency basis in Canada and the United States. The concentration of EMB in feed administered to farmed salmon ranges from 1 to 25 (mu)g g^-1. To determine the acute toxicity of the compound to juvenile and adult American lobster (Homarus americanus), commercial salmon feed was coated with SLICE(trade mark) at a range of concentrations and provided to the animals for 7 d in the laboratory. The LC50 is estimated to be 644 (mu)g g^-1 (95% CI=428, 1275) for adult lobsters and >589 (mu)g g^-1 for stage V and VI juvenile lobsters. The consumption of medicated pellets by adult lobsters decreased significantly with increasing concentration of EMB. Adult lobsters that died during the study had a significantly greater concentration of emamectin B1a in their muscle tissue than those that survived. These results support the conclusion that salmon feed medicated with EMB at the concentrations used by the aquaculture industry is unlikely to pose an acute lethal threat to adult and small juvenile American lobsters.