Comparison of the effect of dichlorvos and pyrethrins against salmon lice (Lepeophtheirus salmonis) parasitic on salmon (Salmo salar) by one or successive treatments

Abstract

Experiments with a flower extract containing Pyrethrins generally used as an insecticide has been carried out at Austevoll Aquaculture Research Station since 1989. Different types of administration methods have been tested and in this report a bath exposure to the treatment solution has been used. Dichlorvos (Nuvan®, Ciba Geigy) and Pyrethrins (Py-Sal 25®, Norsk Pyrethrum A/S) were tested as a delousing agent successively one, two and then six times on individually tagged groups of salmon in the line with regular delousing. The delousing was done in accordance with the advises from the producers of the treatment solutions. The numbers of lice were registered between and after delousing. Delousing was carried out for both treatments at different times of the year to see if any difference in susceptibility to treatment was evident.