DAO 60:123-131 (2004)  -  doi:10.3354/dao060123

Consumption of drugs for sea lice infestations in Norwegian fish farms: methods for assessment of treatment patterns and treatment rate

K. Grave1,*, T. E. Horsberg1, B. T. Lunestad2, I. Litleskare3

1Department of Pharmacology, Microbiology and Food Hygiene, Norwegian School of Veterinary Science,PO Box 8146 Dep., 0033 Oslo, Norway
2National Institute of Nutrition and Seafood Research, PO Box 176 Sentrum, 5804 Bergen, Norway
3WHO Collaborating Centre for Drug Statistics Methodology, Norwegian Institute of Public Health, PO Box 4404 Nydalen, 0462 Oslo, Norway

ABSTRACT: Sea lice are a major problem in Norwegian fish farms; however, data on drug treatment patterns or treatment rates of sea lice infestations are not available. Such data are important for analysing resistance patterns against drugs used for such infestations. The main objective of the present study was to develop a method to estimate the treatment patterns and treatment rates for drugs used in the treatment against sea lice (Lepeophtheirus salmonis and Caligus elongatus) in farm salmonids by means of national sales statistics. Annual sales figures, as weight of active substances, were obtained from the drug wholesalers and the feed mills. The weight of active drug substances is not useful as a unit of measurement of drug use in an epidemiological context because it does not correct for dosage differences and number of repeat treatments. To correct for these factors, we introduced approved daily dose (ADDfarm fish) and treatment course-dosesfarm fish kg–1 live-weight fish. To express the drug treatment patterns, the biomass (in weight) of farm salmonids treated with 1 course of a drug were estimated. When measured as kg active substance, the quantities of drugs for the treatment of sea lice infestations declined by 98% during the study period (1989 to 2002) but this figure increased 5-fold when it was corrected for differences in dosage. To correct for amounts of farm salmonids liable to require treatment we estimated the annual treatment rate, defined as the number of treatments for sea lice infestations per biomass slaughtered Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss. The annual treatment rate increased gradually during the study period; however, it varied considerably (range 0.45 to 1.34, mean 0.90). Before 1995, organophosphates were the most frequently used drugs against sea lice; since then pyrethroids have become the dominating drug group.


KEY WORDS: Sea lice · Drug use · Course-dose · Treatment patterns · Treatment rates


Full article in pdf format