Assessment of the freshwater treatment to control the sea lice Caligus rogercresseyi Boxshall & Bravo, 2000

Sea lice were collected from two salmon farms located in Calbuco, southern Chile to assess the tolerance of Caligus rogercresseyi to freshwater treatment. The first study was carried out in December 2012 in Huito Channel, where salinity reached 26. The second study was carried out in April 2013 in Chidhuapi Channel, where salinity reached 32. In the first study the tolerance of males and females exposed directly to freshwater was assessed, and also the tolerance of C. rogercresseyi infesting rainbow trout (Oncohrynchus kisutch) exposed to bath treatment with freshwater for 30 min. In the second study the tolerance of males and females to a different gradient of salinity was assessed, and also the tolerance of copepodids to reduced salinity. In the first study 100% of males and females were unconscious after 30 min of exposure. However, once they were returned to seawater the survival in males was 93%, 73% in gravid females and 100% in females without egg strings. In the second study a survival of 45% females was recorded and 20% males kept at salinity of 15 for 24 h. However, copepodids were not able to survive at a salinity of 25. The efficacy recorded in the detachment of C. rogercresseyi from rainbow trout treated with freshwater was only 57%, with a higher tolerance of females in comparison with males. Lice collected from the site with salinity of 26, showed major tolerance to freshwater compared with lice collected from the site with salinity of 32.