Factors affecting the abundance of Caligus rogercresseyi (Boxshall and Bravo) on farmed salmonids in Chile in the period 2006–2007

• We assessed the risks factors affecting the abundance of C. rogercresseyi.
• Lice abundance was similar in rainbow trout and Atlantic salmon.
• Geographical and oceanographic characteristics influenced the lice abundance.

An epidemiological study was carried out in the period 2006–2007 to identify the factors that affected the abundance of Caligus rogercresseyi in the two susceptible salmonid species reared in Chile, rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). The differences recorded between four aquaculture zones were mainly a consequence of the geographical and oceanographic characteristics of each location. The values of abundance were significantly influenced by the environmental variable salinity, temperature and water transparency. In addition, the stocking density, the season of year, level of exposure, depth of water at the farm and cage location, were important variables influencing the abundance of sea lice. No significant differences in sea lice abundance were recorded between rainbow trout and Atlantic salmon.