The epidemiology of the sea lice, Caligus elongatus Nordmann, in marine aquaculture of Atlantic salmon, Salmo salar L., in Scotland

Abstract

Although Caligus elongatus is one of two major species of sea lice that parasitize farmed salmon, its epidemiology has not been extensively studied. In this communication, the abundances of the adult stage of C. elongatus in salmon populations from 33 farms in the West of Scotland between 1997 and 2000 have been analysed for evidence of seasonal and annual patterns. The findings indicate that the pattern of C. elongatus is remarkably consistent from year to year, and directly opposed to that reported for Lepeophtheirus salmonis, the other major caligid species. In particular, adult infestations rapidly increase from the start of July each year, and are more prevalent on salmon in the first year of production than the second year. Treatment is seen to have an effect on levels of infestation but it is not clear why this species should have significantly lower levels of abundance in the second year of production. There is also evidence that fallowing has no effect on abundance. Strategic management programmes for the control of sea lice on salmon farms, which are increasingly effective in controlling L. salmonis, may also have to give greater consideration to C. elongatus.

How sea lice from salmon farms may cause wild salmonid declines in Europe and North America and be a threat to fishes elsewhere

“…Young-of-the-year herring, Clupea pallasi While farm data show replacement of Caligus species by L. salmonis on farms (Revie et al 2002;Saksida et al 2007b), there can also be positive correlations in both species abundance on farmed salmon . Such contrasting correlations may be due to density-dependent competition between the species, whereby populations of both species may increase until the larger L. salmonis begins to displace C. elongatus.…”

Infection of wild fishes by the parasitic copepod Caligus elongatus on the south east coast of Norway

“…Anecdotal evidence suggests that these infections occur suddenly in the form of adult lice, and that there seems to be no prior build-up of the C. elongatus population in the form of juvenile stages. Such a transfer process could explain the marked increases in abundance of adult lice in Scotland from the start of July (Revie et al 2002).…”

Identifying epidemiological factors affecting sea lice Lepeophtheirus salmonis abundance on Scottish salmon farms using general linear models

“…The basis of the findings comes from an in-depth analysis of recorded sea lice counts over a 5 yr period from commercial farms across Scotland, and was made available by an industrial partner (Revie et al 2002b). A 2-stage approach was adopted.…”