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Diseases of Aquatic Organisms

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DAO 50:29-33 (2002)  -  doi:10.3354/dao050029

Field trials in Norway with SLICE® (0.2% emamectin benzoate) for the oral treatment of sea lice infestation in farmed Atlantic salmon Salmo salar

A. Ramstad1, D. J. Colquhoun2, R. Nordmo*,1, I. H. Sutherland3, R. Simmons4

1VESO Vikan AkvaVet, Alhusstrand, 7800 Namsos, Norway
2National Veterinary Institute, Section for Fish Health, PB 8156 Dep., 0454 Oslo, Norway
3Easter Rubislaw, Edinburgh, Scotland, UK
4Schering-Plough Animal Health, 1095 Morris Ave., Union, New Jersey 07083, USA
*Corresponding author. E-mail:

ABSTRACT: Four commercial salmon farms on the West coast of Norway were recruited to a programme of field trials in which the efficacy of SLICE® (0.2% emamectin benzoate; Schering-Plough Animal Health) was compared with a commercially available product, EKTOBANN® (teflubenzuron 2 g kg-1; Skretting A/S) in treating natural sea lice Lepeophtheirus salmonis infections in Atlantic salmon Salmo salmar L. At each test site, 3 fish pens were treated with each product. In total, nearly 1.2 million first-year-class fish were included in the trial, of which approximately 561000 received emamectin benzoate at a dosage of 50 µg kg-1 body wt d-1, while approximately 610000 received teflubenzuron at a dosage of 10 mg kg-1 body wt d-1. Medicated feed was provided at 0.5% body wt d-1 over 7 consecutive days. Feed containing emamectin benzoate was generally well accepted by the fish and no problems were encountered in feeding the medicated diet at the desired dose. Lice numbers were counted 2 d before and 1, 7, 14 and 21 d after commencement of treatment. While treatment with both substances rapidly reduced lice numbers, pens treated with emamectin benzoate were found to harbour significantly fewer lice 14 and 21 d post-treatment. Twenty-one days following treatment with emamectin benzoate the lice abundance was reduced on average by 94%. Limited sampling outside the main study period indicated that emamectin benzoate protects against sea-lice infestation over longer periods.

KEY WORDS: Sea lice · Lepeophtheirus salmonis · Caligus elongatus · Salmo salar · Emamectin benzoate

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