The Lice


The genera Lepeophtheirus and Caligus parasitize marine fish, in particular those species that have been recorded on farmed salmonLepeophtheirus salmonis and various Caligus species are adapted to salt water and are major ectoparasites of farmed and wild Atlantic salmon. Several antiparasitic drugs have been developed for control purposes. L. salmonis is the best understood in the areas of its biology and interactions with its salmon host.


Some evidence indicates that sea lice flourishing on salmon farms can spread to nearby wild juvenile salmon and devastate these populations. Sea lice, particularly L. salmonis and various Caligus species, including C. clemensi and C. rogercresseyi, can cause deadly infestations of both farm-grown and wild salmon. Sea lice migrate and latch onto the skin of wild salmon during free-swimming, planktonic nauplii and copepodid larval stages, which can persist for several days. Large numbers of highly populated, open-net salmon farms can create exceptionally large concentrations of sea lice. When exposed in river estuaries containing large numbers of open-net farms, mathematical models have suggested that many young wild salmon may be infected. Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable.

Public Reporting

All feedlot operators are required to report sea lice numbers quarterly and three months in arrears.

It is a requirement that if there is an average of 3 adult female sea lice per fish found during a weekly count on any fish farming site in Scotland, this must be reported to the FHI. Where the reporting level is reached, the FHI will increase the monitoring of that site and continue to do so until either the average adult female sea lice count per fish is reduced to below the reporting level of 3, or an intervention limit of an average of 8 adult female sea lice

per fish on any fish farming site is reached. Reaching the intervention limit requires the implementation of an explicit action plan, agreed with the FHI, which will reduce and maintain

the average number of adult female sea lice per

Sea Lice Policy - Enforcement Regime

fish at the site below the reporting level of 3. If satisfactory measures cannot be demonstrated then enforcement action will be taken.

What Actually Happens

More to follow...

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