Evaluation of emamectin benzoate and substance EX against salmon lice in sea-ranched Atlantic salmon smolts

Abstract

Experimental releases of Atlantic salmon smolts treated with emamectin benzoate (EB) against salmon lice have previously been used to estimate the significance of salmon lice on the survival of migrating smolts. In recent years, the salmon louse has developed reduced sensitivity to EB, which may influence the results of such release experiments. We therefore tested the use of 2 anti-lice drugs: EB was administered to salmon smolts in high doses by intra-peritoneal injection and the prophylactic substance EX (SubEX) was administered by bathing. A third, untreated control group was also established. Salmon were challenged with copepodids of 2 strains of salmon lice (1 EB-sensitive strain and 1 with reduced EB-sensitivity) in mixed-group experimental tanks. At 31 d post-challenge, the numbers of pre-adult lice on treated fish were around 20% compared with the control fish, with minor or no differences between the 2 treatments and lice strains. Both treatments therefore appeared to give the smolts a high degree of protection against infestation of copepodids of salmon lice. However, significantly lower growth of the EB-treatment group indicates that bathing the fish in SubEX is less stressful for smolts than intraperitoneal injection of EB.

Sea trout adapt their migratory behaviour in response to high salmon lice concentrations

“…The assumed duration of the protection from EB was 9 weeks (Glover et al, 2010), whereas subEX protects the fish against lice infestation development for up to 16 weeks (Skilbrei et al, 2015). Treatment with subEX is considered less stressful for the fish than EB, but the treatments with dose and administration as in our study are comparable in efficiency for both sensitive and less sensitive strains of salmon lice (Skilbrei et al, 2015). Results were not affected by these different treatments because excluding 2012 from the analyses gave similar results.…”

“…The prophylaxes also differed in the administration procedure: EB was injected directly into the body cavity right after tag implantation at a dosage of 400 lg EB/kg fish (Glover et al, 2010), whereas subEX was administered by bathing the fish in a 2 mg/L solution for 30 min in a 50-L aerated tank. The assumed duration of the protection from EB was 9 weeks (Glover et al, 2010), whereas subEX protects the fish against lice infestation development for up to 16 weeks (Skilbrei et al, 2015). Treatment with subEX is considered less stressful for the fish than EB, but the treatments with dose and administration as in our study are comparable in efficiency for both sensitive and less sensitive strains of salmon lice (Skilbrei et al, 2015).…”

“…In 2012, the fish were treated with emamectin benzoate (EB), and in 2013-2014 with substance EX bath treatment (subEX; Pharmaq, Norway). The prophylaxes differ in their mechanism: EB is a neural toxin and kills all attached lice (Burka, Fast, & Revie, 2012;Glover, Samuelsen, Skilbrei, Boxaspen, & Lunestad, 2010), whereas subEX is a chitin synthesis inhibitor and therefore inhibits moulting to the next stage (Skilbrei, Espedal, Nilsen, Garcia, & Glover, 2015). The prophylaxes also differed in the administration procedure: EB was injected directly into the body cavity right after tag implantation at a dosage of 400 lg EB/kg fish (Glover et al, 2010), whereas subEX was administered by bathing the fish in a 2 mg/L solution for 30 min in a 50-L aerated tank.…”

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

“…This treatment was applied to 50% of the fish, randomly selected, securing a balanced design. SubEX protects the fish by preventing attached copepodids to develop into the next life stage for up to 16 weeks after treatment (Skilbrei, Espedal, Nilsen, Garcia, & Glover, 2015). Identical (sham) treatment was performed on the control fish.…”

Impacts of parasites on marine survival of Atlantic salmon: a meta‐analysis

“…In each trial, smolts have been tagged and assigned to one of two groups: control or antiparasitic treatment. Two different antiparasitic treatments have been used, emamectin benzoate (with marketing authorization, oral administration via feed or as intraperitoneal injection) and Substance Ex [without marketing authorization, chitin synthesis inhibitor, topical bath treatment (Skilbrei et al 2015)]. Because individual fish in each trial are tagged, recovery programs for recruits can then identify these fish and calculate the difference in survival between the control and treatment groups.…”