The acute lethality of three anti-sea lice formulations: AlphaMax®, Salmosan®, and Interox®Paramove™50 to lobster and shrimp

• Lethal thresholds for three anti-louse pesticide formulations are presented.
• Lobsters and shrimp are sensitive to the active ingredients during 1-hr exposures.
• Lethality ranking: Alphamax® > Salmosan® > Paramove®.
• Alphamax® is lethal at a 2000-fold dilution of prescribed treatment concentration.
• Salmosan® and Paramove® are lethal at or near prescribed treatment concentration.

Several pesticide formulations have been used in eastern Canada to treat infestations of sea lice on Atlantic salmon since the mid-1990s. Traditionally 48 and 96 h exposure periods are used to assess potential hazards of chemicals to non-target organisms. Exposure of this duration is not considered representative of exposure scenarios in southwest New Brunswick, Canada. Lobsters and shrimp were exposed to the pesticide formulations, AlphaMax® (active ingredient deltamethrin), Salmosan® (azamethiphos) and Interox®Paramove™50 (hydrogen peroxide) for 1 or 24 h and lethal thresholds were determined. The recommended treatment concentrations reflect the relative toxicity of the three formulations to the sea louse. AlphaMax® is applied at 2 μg L− 1 as deltamethrin, Salmosan is applied at 100 μg L− 1 as azamethiphos and Interox®Paramove™50 is applied at 1200–1800 mg L− 1 as hydrogen peroxide. The formulations also affect the species used in our studies in the same relative order. AlphaMax® is the most toxic formulation with LC50s reported in the ng L− 1 (as deltamethrin) range, up to a 2000-fold dilution of the recommended treatment concentration. Lethal thresholds for Salmosan® are in the μg L− 1 (as azamethiphos) range with a maximum 30-fold dilution of the recommended treatment concentration to reach the lethal threshold for the most sensitive species tested. Interox®Paramove™50 was the least toxic formulation tested in our studies with the lowest LC50 approximately equal to the recommended treatment concentration, as hydrogen peroxide.