Wild and farmed mussels, Mytilus edulis, coexist with salmon farms in Scottish sea lochs. A synthetic
pyrethroid,
cypermethrin, is licensed for use on fish farms to control sea
lice infestations as a formulation called Excis. In this study, uptake of
cypermethrin from Excis exposure is investigated through the use of gas chromatography with mass-spectrometry. The effects of Excis on mussels are also examined by measuring the
neutral red retention time of lysosomes, aerial survival and shell closure. The isomeric ratios of cis:trans
cypermethrin measured in mussels are around 80:20; a marked increase from 40:60 to which the mussels were exposed. This is most likely due to preferential metabolism of trans-isomers, as the same response is seen in vertebrates. There is a pronounced behavioural effect of shell closure, where mussels exposed to 1000 microg/l
cypermethrin shut their shells within an hour of exposure. Arguments are presented for this effect being either a voluntary response on recognition of
cypermethrin, or an effect arising from an involuntary action of
cypermethrin on the adductor muscle. Even at 1000 microg/l
cypermethrin,
neutral red retention time and aerial survival are not affected. The data suggest that the responses of mussels shown here are unlikely to occur in the field, even at the concentrations of
cypermethrin used in fish cages, for the treatment of sea lice.