The main indication for use of avermectins in aquaculture-produced fish is infestations with ectoparasitic copepods.
The compounds ivermectin and emamectin benzoate are predominantly used as in-feed formulations on salmonid
fish against copepods in the family Caligidae: Lepeophtheirus salmonis, Caligus elongatus and C. rogercresseyi. These
agents are well-documented as very effective on all developmental stages of the parasites. The duration of effect can be up
to 10 weeks. The safety margin for ivermectin is narrow, but better for emamectin benzoate. Environmental impact from
these chemicals on bottom-dwelling and sediment-dwelling organisms occurs, but these are restricted to the immediate
area around the production site. Avermectins are incompletely absorbed from the intestine of the fish and slowly excreted.
They penetrate the blood-brain barrier of the fish, ivermectin more than emamectin benzoate. Resistance has developed
against these agents in L. salmonis in almost all major salmon producing areas. The situation must be viewed as serious
and can render these agents completely ineffective for salmon lice control.
Keywords: Emamectin, ivermectin, fish, salmon, trout, sea lice
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