Effectiveness of teflubenzuron for treating sea lice on Atlantic salmon: Randomized control clinical trial, historical control clinical trial, and an assessment of outcome measurements and sampling methods

A double-blind, randomized clinical trial was performed to investigate the effectiveness of teflubenzuron to control sea lice (Lepeophtheirus salmonis) on cage reared Atlantic salmon (Salmo salar). The teflubenzuron was administered in the feed at a dosage of 10 mg/kg biomass/day for seven days. Chalimus stages in medicated cages were significantly lower than in control cages at one week (79% reduction, p < 0.001), and at two weeks (53% reduction, p < 0.001). Mobile (pre-adult and adult) stages were also significantly reduced in medicated cages at one week (69% reduction, p < 0.01), and at two weeks (40% reduction, p < 0.01). These reductions may underestimate the full potential of teflubenzuron, due to the low parasite levels experienced during the summer of 1996, and due to recruitment from the untreated cages. A historical control clinical trial was also performed at one site using teflubenzuron administered in the feed at a dosage of 10 mg/kg biomass/day for seven days. This study involved the treatment of all nine cages on site. Six of the cages were pre-market size salmon and three cages contained smolt. At one week after the end of treatment chalimus stages were reduced by 92% (p < 0.05) and mobile stages were reduced by 74% (p < 0.05) from pre-treatment levels. Two weeks after the end of treatment chalimus stages were reduced by 41% (p < 0.05) and mobiles were reduced by 61% from pre-treatment levels. Three weeks after the end of treatment chalimus stages were still reduced 36% (p < 0.05) from pre-treatment levels, but mobile stages had increased by this time. (Abstract shortened by UMI.).