Monitoring and potential control of sea lice using an LED-based light trap

Sea lice are ectoparasitic copepods that threaten salmon farming aquaculture and the viability of wild salmon populations. To control infestations on farmed salmon, several chemotherapeutants have been developed, but these are invasive (often causing fish stress and loss in production), costly, may induce parasite resistance over time, and their impact on the environment is a major social concern. Here, we show that a light-emitting diode (LED)-based light trap can be used to monitor sea lice presence on fish and in the water. The performance of the light trap was tested in experimental tanks and in the ocean. Plankton net tows were also performed to compare catches with those from light traps. The light trap caught similar to 70% of salmon lice larval stages loaded onto a tank and similar to 24% of the adults. It also acted as a delousing agent by removing similar to 8% of adult salmon lice infective on Chinook salmon ( Oncorhynchus tshawytscha) smolts in tank experiments. In the ocean, the light trap caught 21 sea lice (10 Lepeophtheirus salmonis and 11 Caligus clemensi), comprising free-swimming and attached stages, while plankton net tows failed to capture any. We conclude that light traps constitute an effective, noninvasive, environmentally friendly method to monitor sea lice.