Efficacy of emamectin benzoate in the control of Caligus rogercresseyi on farmed Atlantic salmon (Salmo salar L.) in Chile from 2006 to 2007

Caligus royercresseyi (Boxshall and Bravo, 2000) has been one of the greatest challenges for the salmon farming industry in Chile since 1997. A field study was carried out in four areas of Region X in the period 2006–2007 to obtain information about the efficacy of emamectin benzoate in the control of C. rogercresseyi in farmed Atlantic salmon (Salmo salar), one of the susceptible salmon species reared in Chile. The results obtained in this study show that the differences observed in the values of prevalence and abundance between the four areas in Region X were mainly caused by the oceanographic conditions and not as a consequence of the number of treatments with emamectin benzoate applied in the period of study, which on average ranged between 8 and 14 treatments by area.

► Failures of the treatments with emamectin benzoate are explained by the lost of sensitivity of C. rogercresseyi. ► Differences in prevalence and abundance of C. rogercresseyi are explained by the oceanographic conditions. ► Salinity is the main variable affecting the abundance of C. rogercresseyi.