BACKGROUND
Sea lice are the most economically and environmentally serious ectoparasite of marine salmonids. Sea lice have been largely controlled by treating with a variety of medicines. In order to understand sustainability of medicine usage an analysis of sea lice treatment data has been carried out for all Scottish salmon farms from 2005 to 2011.

RESULTS
Overall, there was an increase from 0.156 to 0.282 treatments month(-1) ; treatments could involve one or multiple agents. This increase was mostly in bath treatments (cypermethrin in 2007 largely replaced by deltamethrin and azamethiphos in 2008). Treatments using in-feed treatments (emamectin benzoate and teflubenzuron) increased only slowly. Treatments involving more than one medicine in a single month also increased, as did the probability of follow-up treatments. Treatments were seasonal with peaks of in-feed treatments in March and August and bath treatments more frequent between August and December.

CONCLUSION
Frequency of sea lice treatment increased substantially, with an increase in multi-agent and follow-up treatments. This increase in treatment activity is expensive to industry and increases exposure of the neighbouring environment. This indicates earlier lice control practices were not sustainable.