Optimization of calcium oxide treatment against salmon louse (Lepeophtheirus salmonis). A controlled laboratory study

Salmon louse ( Lepeophtheirus salmonis ) infestations pose a significant challenge to the salmonid farming industry. While most conventional water-treatment protocols primarily target lice at parasitic stages once attached to the fish, preventive measures targeting planktonic/free-living stages are scarce. This study investigated the effects of fine calcium oxide (CaO) particles on salmon louse planktonic stages under controlled laboratory conditions. The study tested a range of concentrations (0.2 g/L to 0.6 g/L) exposure times (2–15 minutes) and frequency of exposures (from daily to every five days). The results indicated that the effects of CaO exposure were positively correlated with the concentration, duration, and frequency of the treatment. Exposure to CaO (10 minutes at 0.2 g/L) reduced by 60–70 % the number of nauplii reaching the copepodid stage by decreasing survivability and molting. CaO treatment (10 min at 0.6 g/L) induced up to 90 % mortality of free-living copepodids. In infection trials using copepodids that survived CaO treatment, there was a 42.1 % reduction in the number of parasitic chalimus, pre-adult, and adults on the salmon five weeks post-infection as compared to control. The LC 50 for copepodids ranged between 0.54- and 0.36-g/L for an exposure time of 2–10 minutes, respectively. This laboratory study serves as an essential first step in validating the efficacy of CaO and establishes a foundation for future field trials to assess its potential as an antiparasitic treatment in aquaculture. • CaO exposure at 0.2 g/L for 10 min reduce nauplii reaching copepodid stage by 60–70 %. • 10 min exposure to 0.6 g/L CaO caused up to 90 % mortality of free-living copepodids. • CaO-treatment (0.2 g/L for 10 min) reduces copepodid infestation success by 65 %. • CaO LC 50 for copepodids is 0.54–0.36 g/L for 2–10 minutes exposure respectively.