Development of a Management Strategy for the Reduction/Elimination of Sea Lice Larvae, Lepeophtheirus salmonis, Parasites of Salmon and Trout

Abstract

Sea lice are copepod ectoparasites of fish, belonging to the family Caligidae. Their importance to marine salmonid culture stems from the extensive damage they may inflict on hosts through feeding and contact abrasion. The principal species associated with cultured salmonids is Lepeophtheirus salmonis (Kroyer, 1838), a large salmonid-specific species reported as a problem for aquaculture in a number of countries. The objectives of the present study were: (a) to examine the production and distribution of larval stages of Lepeophtheirus salmonis within a cage containing Salmo salar in order to identify specific spawning cues and larval frequencies and intensities; (b) to identify precisely the behavioural patterns of sea lice larvae over a variety of tidal and diurnal cycles; (c) to monitor environmental parameters and (d) having identified the specifics of spawning and larval behaviour, to identify potential management strategies for the elimination of a high percentage of sea lice larvae produced on fish farms. Larval plankton samples along with mobile lice samples were taken during two growing cycles on a fish farm on the west coast of Ireland. Highest densities of larvae were recovered during neap tides following synchronous spawning episodes within the female population. Gravid females were recorded during the winter months; however, spawning intensity remained low until late Spring. Sea lice larvae migrated vertically within the water column with highest densities recorded during slack water normally associated with high tide. The results of this study increases our knowledge of the complex behaviour and life cycle of the louse. The occurrence and the location of high densities of larvae within salmon cages have been identified. This information provides a sound basis from which management strategies can be developed in order to reduce lice intensities on the farm.