Sea Lice: Views from the Veterinary Corner
IAAAM Archive
Grace A. Karreman
Pacific Marine Veterinary Services
Nanaimo, BC, Canada


Sea lice (Lepeophtheirus salmonis) have been central to a controversial issue worldwide. In British Columbia where there are both resident wild stocks and a growing salmon aquaculture industry the controversy has been particularly acute. Much of the scientific information has come from European studies. There has been less work done on Pacific species, on farmed Atlantic species in Pacific waters and on the dynamics of infection between wild and farmed stocks in Pacific waters.

Baseline information on farmed stocks has been obtained as of the fall 2003, when the British Columbia Ministry of Agriculture Fisheries and Foods (BC MAFF) mandated that Atlantic salmon farms do monthly or more frequent counts of lice on their salmon. Numbers have been reported to BC MAFF on a regional (watershed) basis and posted at Preliminary data from the farms showed regional differences in average levels of infection and that age of the fish appears to be a factor in intensity of infection.

In 2003 Fisheries and Oceans Canada (DFO) undertook several research initiatives concerning sea lice in wild stocks in coastal areas of British Columbia. In particular the Broughton area (eastern Queen Charlotte Strait and its inlets) has been intensively surveyed. However, further work is still required. Preliminary findings indicate that baseline information is still incomplete with regard to the wild host species, pathogen and the environment. There are previously unrecognized over wintering populations of juvenile salmon. Early stages of L. salmonis have been found on at least one non-salmonid species. Oceanographic measurements indicate that the region is not uniform with regard to current and salinity.

With insufficient baseline information the dynamics of infection between wild and farmed stocks cannot be fully assessed. An additional underlying question has been how to measure the health of the wild populations and indirectly, the potential impact of sea lice on the health of those populations. One approach has been to look at estimates of population abundance and/or individual fish characteristics such as condition factor. A complementary approach has been to use medical estimates of health, for example, post mortem examination and clinical pathology from individuals in the same population. Preliminary findings have led to several hypotheses that will require further testing.

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Grace A. Karreman