The duration of efficacy following oral treatment with emamectin benzoate against infestations of sea lice, Lepeophtheirus salmonis (Krøyer), in Atlantic salmon Salmo salar L.

Abstract

The duration of efficacy of emamectin benzoate in the oral treatment of sea lice, Lepeophtheirus salmonis, infesting Atlantic salmon, Salmo salar L., was evaluated in a tank study. One group of salmon was treated at a nominal dose of 50 μg kg−1 biomass day−1 for 7 consecutive days and a second group was untreated. Fish were then redistributed to 16 tanks, each holding 17 control and 17 treated fish. On days 34, 41, 48, 55, 62, 69, 76 and 83, two tanks were challenged with L. salmonis copepodites. Eight to 14 days after each challenge, fish were anaesthetized and numbers of lice recorded. Treatment with emamectin benzoate prevented development of copepodites for up to 62 days from the start of treatment, and chalimus numbers remained low for 69 days. Treated fish, challenged from days 34 to 69, had significantly (P<0.01) fewer lice than control fish. Treated fish challenged at days 76 and 83 still had fewer lice than control groups, although differences were not statistically significant for both replicates. When chalimus appeared on treated fish challenged at days 69–83, survival of chalimus to adult stages was lower than on control fish. Louse egg production on treated fish challenged at days 62–83 was not reduced compared to control groups.

Reduced Lepeophtheirus salmonis larval abundance in a sea loch on the west coast of Scotland between 2002 and 2006

“…Furthermore, the use of a smoothing function in the models may overlook any short-lived changes in larval densities. The sustained period of low densities of nauplii and copepodids between production Weeks 60 and 70 of Cycle 1 occurred immediately after the emamectin benzoate treatment and is consistent with a prolonged protection against L. salmonis that this treatment can afford (Stone et al 2000c.…”

“…Furthermore, the use of a smoothing function in the models may overlook any short-lived changes in larval densities. The sustained period of low densities of nauplii and copepodids between production Weeks 60 and 70 of Cycle 1 occurred immediately after the emamectin benzoate treatment and is consistent with a prolonged protection against L. salmonis that this treatment can afford (Stone et al 2000c.The emamectin benzoate treatments applied in the first half of Cycle 2 appeared to have suppressed the increase in Lepeophtheirus salmonis abundance at Farm 1. Prior to the wider availability of emamectin benzoate, Revie et al (2002) found that L. salmonis abundance typically increased on Scottish farms near the end of the first year.…”

“…Cypermethrin does not remove all stages of Lepeophtheirus salmonis (Hart et al 1997), and applications of this medicine often result in short-lived decreases of 2 to 3 wk in L. salmonis burdens at farms (Revie et al 2002) and treatment success can vary (Sevatdal et al 2005). However, emamectin benzoate is active against chalimus, pre-adult and adult stages of L. salmonis (Stone et al 2000a,b) and confers protection against recruitment that lasts approximately 10 wk (Stone et al 2000c. Therefore, applications of emamectin benzoate may provide a more detectable signal than that of cypermethrin.…”

Oral l-cysteine ethyl ester (LCEE) reduces amoebic gill disease (AGD) in Atlantic salmon Salmo salar

“…Fish were lethally sampled pre and post the 2 wk medicated feed period. This type of experimental design, using 1 tank per feeding treatment during an initial medication phase has been used before by Stone et al (2000). After the 2 wk medica-tion period, 6 fish from each treatment were transferred to individual flux boxes to measure net [H + ] and total ammonia fluxes (see 'Whole body ionic flux').…”

Efficacy of emamectin benzoate in the control of Argulus coregoni (Crustacea: Branchiura) on rainbow trout Oncorhynchus mykiss

“…The efficacy of emamectin benzoate (50 µg kg -1 for 7 d) has been demonstrated against the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus on Atlantic salmon Salmo salar (Stone et al 1999, 2000a,b,c, Treasurer et al 2002, and Salmincola edwardsii on brook trout, Salvelinus fontinalis (Duston & Cusak 2002). Stone et al (2000a) ascertained that the duration of efficacy against L. salmonis on salmon was up to 10 wk. The mode of action of avermectins is to increase the permeability of chloride ions in the neurons of invertebrate inhibitory synapses, which results in the paralysis and death of ectoparasites infesting fish (Arena et al 1995, Vassilatis et al 1997.…”