The development of pyrethrum-based treatments against the ectoparasitic salmon lice Lepeophtheirus salmonis in sea cage rearing of atlantic salmon Salmo salar L
2001
Boxaspen, K. | Holm, J.C.
Motile salmon lice Lepeophtheirus salmonis were successfully removed by an oil-based pyrethrum treatment mixture. The experiments described here are all based on skin exposure of the salmon Salmo salar L. The in-cage method, in which salmon would delouse themselves by jumping through a layer of treatment mixture, gave up to 86.9% delousing effect under low levels of solar radiation (October). However, at higher levels of radiation (May), the comparable effect decreased to 31.8%. Studies of exposure time vs. delousing effect showed no difference between 2-s and 10-s exposure and gave an overall delousing effect of 89.5%. Individual delousing procedures have thus been developed with a 4- to 6-s dip in the pyrethrum treatment mixture. A commercial method is described based on commercial Py-Sal 25 mixed with an anaesthetic bath before a vaccination or sorting operation. The overall delousing efficiency with this large-scale method was 85%. This is the method now used in commercial delousing with pyrethrum as the active component.
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