A survey was carried out between March 2006 and February 2007 on the fecundity of Caligus rogercresseyi in four areas of Region X (Lat 42 degrees S) in Chile. An average length of 4.83 +/- 0.4 mm for gravid females and 4.78 +/- 0.56 mm for males was recorded from the four areas, with no significant differences in length between sexes. Although females were largest in spring and summer, egg strings were longer and there were higher number of eggs per string in winter. The lowest salinity values were recorded in the Hornopirén area, which had the largest gravid females and the highest number of eggs per string during the study. The number of lice treatments showed no influence on the fecundity rate in the four areas. Prevalence and abundance of C. rogercresseyi were influenced by salinity and temperature.