New case study: hydrogen peroxide for sea lice control

Control of sea lice infections using hydrogen peroxide at reduced salinities

Sea lice are a significant health challenges in salmon farming, causing stress, reduced growth, and significant economic losses. Hydrogen peroxide (H₂O₂) is widely used in bath treatments to remove lice - its rapid breakdown into water and oxygen leaves no harmful residues. This project investigated whether combining H₂O₂ treatments with reduced salinity - another method known to stress lice - could improve effectiveness without harming fish.

Valued at £243K, the project partners were DawnFresh, Solvay Interox Ltd, Mowi Scotland, Aqua Pharma Ltd and the University of Stirling. The project received funding from, and was supported by, SAIC.

Researchers tested how H₂O₂ interacts with water of different salinities, its impact on pH, and whether these changes remain safe for salmon. They also assessed lice susceptibility and treatment outcomes in both lab and practical conditions.

The team found that adding H₂O₂ caused only minor pH changes, well within safe limits for salmon. In lab bioassays, low salinity and H₂O₂ appeared to have additive effects on lice, suggesting potential benefits. However, in live fish trials, combining H₂O₂ with reduced salinity did not improve lice clearance compared to standard seawater treatments. No fish mortality or abnormal behaviour occurred during treatments.

The study highlights a key difference between lab and real-world results: while bioassays showed promise, practical trials did not support the use of low salinity with H₂O₂ for better outcomes. Commercial data from trout farms also showed highly variable success rates unrelated to salinity, suggesting other factors influence treatment efficacy.

H₂O₂ remains a safe and effective option for sea lice control at standard salinity, but lowering salinity during treatment offers no clear advantage. These findings help refine best-practice guidelines, ensuring treatments are both safe and efficient without unnecessary complexity.

The full title of this project is ‘Control of sea lice infections of farmed salmonids using hydrogen peroxide’.

Read the case study