Salmon lice can impact the marine behaviour, growth, and survival of salmonids, but little is known about their effects on Arctic char. We present behavioural responses from the first dose-response experiment with wild anadromous Arctic char (n = 50) infested in situ with salmon lice (0.0–1.2 lice g⁻¹ fish) in an area with low natural infestations. Infested fish spent less time at sea ...