Effects of food borne ivermectin on juvenile Atlantic salmon (Salmo salar L.): Survival, growth, behavior, and physiology

Abstract

Ivermectin (Eqvalan®) (IVM) has been widely used as an oral treatment of sea lice (Lepeophtheirus salmonis Caligus sp.) infestations of farmed Atlantic salmon (Salmo salar L.). We report the use of a suite of behavioral, physiological (growth, liver somatic index, brain acetylcholinesterase (brain AChE) and vitellogenin (Vg)) responses to explore the effects of dietary doses of IVM on juvenile Atlantic salmon. Brain AChE was measured because of IVM's neurological activity and its ability to cross the blood–brain barrier. Induction of plasma Vg was used as a measure of IVM's possible estrogenicity. Fish were treated as follows every third day for 30days: (a) low dose 0.05mgkg−1bodyweight (bw), (b) high dose 0.25mgkg−1bw, and (c) control (0mgkg−1bw). After 30days, half the fish from each tank were sampled. The remaining fish were held for 30 additional days on a clean diet to observe the potential for recovery. Cumulative mortalities of 5% and 70% were observed in the low dose and high dose IVM treatments respectively. Fish weight and condition factor were reduced after 30days in the high dose IVM treatments (p<0.05). Liver somatic index (LSI) was significantly reduced in the female fish treated with low dose IVM after 30days of depuration (p<0.05). Fish dosed with IVM had apparently reduced mobility and took longer to complete feeding. Male dosed fish had significantly higher brain AChE activity (p<0.05). Plasma Vg was lower (p<0.05) in the high dosed female fish after 30days. Vg was also lower in the low dosed female fish (p<0.05) after the depuration period. These results have importance for aquaculturists in the calculation of rations and therapeutic dosage strategies for the IVM treatment of sea lice infestations in Atlantic salmon.