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(M/FF231) The toxicity of sea lice chemotherapeutants to non-target planktonic copepods. Willis, Kate1, Ling, Nicholas2, Tarling, Geraint1, 1 2 ABSTRACT- Infestations of parasitic copepods or sea lice (Copepoda: Caligidae) on farmed salmonids cause devastating damage when present in large numbers. To control sea lice infestations the salmon farming industry uses chemotherapeutants that are highly toxic to crustaceans and target specific life stages of sea lice. Planktonic copepods are of prime importance in marine ecosystems and have a similar life cycle to parasitic copepods hence they are also likely to be adversely affected by sea lice treatments. The toxicity of three current sea lice treatment chemicals, cypermethrin, emamectin benzoate and teflubenzuron, to common planktonic copepods was investigated using acute laboratory bioassays. Cypermethrin and emamectin are neurotoxic whereas teflubenzuron inhibits chitin synthesis. Acartia clausi, Temora longicornis, Pseudocalanus elongatus and Oithona simillis were collected from Scottish sea lochs and cultured in the laboratory. For each species and chemical, the comparative sensitivity of three life stages (nauplii, copepodites, adults) was determined using acute tests with vigour, immobility and mortality as endpoints. Sublethal effects were investigated by exposing nauplii and copepodites with survival and growth monitored for up to 10 days post-exposure. Cypermethrin and emamectin sensitivity varied considerably between species with high concentrations causing immobility rather than death. Adult animals were insensitive to teflubenzuron but exposure of moulting stages caused mortality and deformity at very low concentrations (~100 ng/L). Bioassay survivors showing sublethal exposure effects to any chemical did not recover, indicating sea lice chemotherapeutants are likely to exert significant ecological effects at concentrations well below indicative LC50 values. Key words: salmon farming, sea lice, copepod, chemotherapeutant toxicity |
