Sea lice outbreaks in salmonid aquaculture can impact both farmed and wild salmon. Anti-sea lice chemotherapeutants used to treat these outbreaks are released directly into the water column after treatment, potentially exposing non-target organisms. Salmosan® (active ingredient: azamethiphos) has recently been approved for use in British Columbia as a sea lice treatment. In the present study, the lethal and sublethal effects of Salmosan® were examined in intermolt and post-molt Pacific spot prawns (Pandalus platyceros). Post-molt prawns were found to be more sensitive than intermolt prawns, and this sensitivity was exacerbated at higher exposure temperatures. Repeated (3 x) 1‑h LC50 values for post-molt prawns were 39.8, 27.1, and 17.1 µg/L at 5, 11 and 17 °C, respectively. All intermolt prawns survived 3 x 1-h exposures up to 100 µg/L azamethiphos at 5, 11 and 17 °C. Intermolt prawns held at 17 °C molted 83 – 91% sooner and experienced 70 – 73% greater mortality than those held at 5 or 11 C; azamethiphos did not affect either of these parameters. In a separate experiment, intermolt prawns displayed an 86 – 103% reduction in antennule flicking, a chemoreception-mediated behavior, at 24 h following repeated (3 x) 1-h exposures to 50 and 100 µg/L azamethiphos. These results may aid in the development of regulatory protocols and guidelines for the use of anti-sea lice pesticides in Canada.
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