Introduction
Parasitic salmon lice (Lepeophtheirus salmonis ) present a significant challenge for salmonid aquaculture in Norway. Allowable lice abundance in commercial farms is strictly regulated, and farmers must engage in extensive delousing operations to adhere to regulatory thresholds. The widespread development of resistance to most available tr eatment chemicals has driven the adoption of mechanical tr eatment alternatives, many of which negatively impact growth, health, and welfare of farmed fish. Controlling measures that effectively reduce salmon lice without negatively affecting health and quality of farmed fish may therefore increase profitability and reduce the environmental footprint of current farming practices. Optical delousing is an alternative method of lice control that do es not require handling of the fish. The system utilizes machine vision and object detection algorithms to identify and remove mobile and adult sea lice st ages with targeted laser pulses on freely swimming fish. It relies on mobile hardware components that are continuously deployed in commercial sea cages, where they are actively positioned close to the fish. Here , we empirically evaluate the need for lice treatments at sites with and without optical delousing.
Materials and Methods
Operational data on lice treatments and lice abundance are publicly available for all aquaculture sites in Norway. We grouped public data from all reportable sites along the Norwegian coast in 2023 into production weeks and added whether optical delousing was used during each production week. To capture possible effects of optical delousing on treatment frequency, we selected generalized linear mixed effects models (GLMEs) and estimated the weekly probability of a treatment taking place, considering sea temperature and the presence of optical delousing as predictors.
Results
Results showed that sites relying on optical delousing represented 10.9% of production weeks, but only 5.9% of treatment weeks. Adjusted for a sea temperature of 10°C, sites without optical delousing had a 10.1% weekly probability to require treatment. For sites with optical delousing, the weekly probability to require other forms of sea louse treatment was significantly reduced by 50% to 5.06%. These differences persisted despite a lower reliance on cleaner fish at sites with optical delousing and in the absence of any indication of an accompanying increase in lice abundance at these sites.
Conclusion
In conclusion, we show that optical delousing can be an effective tool to control lice abundance in salmonid aquaculture along the Norwegian coast without stressful handling of the fish. This may both benefit the health of farmed fish and reduce lice infection pressure on wild salmonid populations.