Caligus elongatus and other sea lice of the genus Caligus as parasites of farmed salmonids: A review

This review was prompted by reports of unusually large numbers of sea lice tentatively identified as Caligus elongatus infesting farmed salmon in northern Norway. Following a brief introduction to the sea lice problem in salmonid aquaculture, the review is divided into a further eight sections. The first is a review of existing information on the life cycle and behaviour of Caligus spp. The second is a description of the morphology of different stages in the life cycle of C. elongatus. The third describes the effects of caligid infestations on salmonid hosts. The fourth reviews information on the geographical distributions and host preferences of the six species of Caligus reported from farmed salmonids in different parts of the world: C. elongatus, C. curtus, C. clemensi, C. rogercresseyi, C. teres and C. orientalis. The fifth section describes interactions between farmed and wild fish and the sixth presents information on the genetics of C. elongatus. A section reviewing the different methods used to control sea lice infestations follows. The eighth section discusses the predicted effects of climate change and invasive host species on the distribution and occurrence of caligid copepods, and the ninth gives conclusions and recommendations on how to further investigate the infestation that prompted this review. These include the confirmation of the identity of the caligid causing the problem, confirmation of the genotype involved and a study of the vertical distribution in the water column of the infective stages.