Relationship between dose of emamectin benzoate and molting response of ovigerous American lobsters (Homarus americanus)

A widely-prescribed treatment to control sea lice on cultured salmon is the administration of feed medicated with SLICE™ (active ingredient emamectin benzoate (EMB)). High doses of EMB can disrupt the molt cycle of ovigerous American lobsters, causing them to enter proecdysis prematurely and lose their attached eggs when the shell is cast. To determine the dose response to EMB, lobsters were forced to ingest doses that ranged from 0.05 to 0.39 μg g−1. A significant proportion of lobsters given doses of 0.39 and 0.22 μg g−1 (37% and 23%, respectively) molted prematurely, almost a year earlier than the control group. All the lobsters in the 0.05 and 0.12 μg g−1 groups molted at the normal time and the mean time of molt was similar to that of the control group. Thus, the no-observed-effect level (NOEL) and lowest-observed-effect level (LOEL) of EMB on the molt cycle were 0.12 and 0.22 μg EMB g−1 lobster, respectively. To acquire the LOEL, a 500-g lobster would have to consume 22 g of salmon feed medicated with SLICE™ at a level of 5 μg EMB g−1 feed.