Control of salmon lice through optical delousing in commercial salmonid aquaculture

Parasitic salmon lice are a major challenge for salmonid aquaculture in Norway. The development of resistance against most available medicines has favored the implementation of mechanical treatment alternatives, many of which have negative implications for the health and welfare of farmed fish. Optical delousing is a controlling measure that continuously reduces salmon lice in commercial sea cages. It relies on machine vision and object detection algorithms to detect salmon lice and remove them with a targeted laser pulse on freely swimming fish. Although this technology is increasingly adopted by the farming industry, an empirical investigation of its effects on treatment frequency and salmon lice abundance has so far been lacking from scientific literature. We analyze publicly available data on salmon lice abundance and treatment frequency at individual aquaculture sites complemented with information on the use of optical delousing for the entire Norwegian coast in 2023. Our results show that sites relying on optical delousing exhibit a 50 % lower weekly treatment probability. Similar differences applied for all treatment categories and persisted despite a reduced reliance on cleaner fish and in the absence of any indication of a concomitant increase in salmon lice abundance at these sites.