Efficacy of ivermectin for control of the salmon louse Lepeophtheirus salmonis on Atlantic salmon

The eff~cacy of orally administered lveimectin against the common salmon louse Lepeophthelrus salmonls on Atlant~c salmon Salmo salar was invest~gated under laboratory condltions Both 3 and 6 doses of ivermectln at a targeted dose of 0 05 m g k g -' f ~s h admin~stered in the feed every third day airested the development and reduced the Intensity of lnfect~on by L s a l m o n ~s This IS the first report of dn eff~cacious treatment a g d ~n s t the chalimus stages of sea lice S e r ~o u s head dnd doisal body lesions, typical of L s a l m o n ~s f e e d ~n g act~vity, which developed on the control f ~s h were absent from the ~vermect~n-tredted f ~s h lvermectin fed at these dosage reglmes resulted in a d a r k e n ~n g of the fish, but appealed not to reduce their feeding activity K E Y WORDS Ivermectin Lepeophthe~rus salmonis Parasite control P a r a s ~t e treatment -Salmon louse .