Sea louse
3826067
225755230
2008-07-15T06:55:37Z
DocWatson42
38455
Performed minor clean up.
{{For|the thimble jellyfish larvae that cause itching in humans|Seabather’s eruption}}
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'''Sea lice''' are [[copepod]]s which [[parasite|parasitise]] fish. There are two species of sea lice commonly found on [[Fish farming|cultured]] [[Salmonidae|salmonids]], ''Caligus elongatus'', a species of parasite that infests over fifty different species of marine [[fish]], and ''Lepeophtheirus salmonis'', which infests only [[salmon]] and closely related species such as [[rainbow trout]] (but current research indicates it may be spread via the [[three-spined stickleback]]). Both species are also found on wild salmon.
There is reported concern that sea lice flourishing on [[Fish farming|salmon farms]] can spread to nearby wild juvenile salmon and devastate these populations.<ref> Martin Krkosek, Jennifer S. Ford, Alexandra Morton, Subhash Lele, Ransom A. Myers, and Mark A. Lewis ([[14 December]] [[2007]]), [http://www.sciencemag.org/cgi/content/summary/318/5857/1711 Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon]. ''Science'' 318 (5857), 1772.</ref> [[Sea trout]] populations in recent years have seriously declined due to infestation by sea lice from salmon farms.<ref>{{cite book |author=Clover, Charles |year=2004 |title=The End of the Line: How Overfishing is Changing the World and What We Eat |publisher=[[Ebury Press]] |location=London |isbn= 0-09-189780-7}}</ref> However, there is still very little known about the larger ecological interactions and it is too early to pinpoint, conclusively, that aquaculture is a major source of lice that infect wild salmon.
As sea lice develop from eggs to adults, they shed their [[exoskeleton]]s in a series of [[ecdysis|moults]]. This creates a number of identifiable life stages. Sea lice in the first two stages are called [[nauplius (larva)|nauplii]]. Nauplii can neither feed nor attach themselves to fish. In the next, copepodid, stage, the lice can attach themselves to fish. They then moult through four chalimus stages during which they are anchored to a host fish. As pre-adults (two stages) and adults (one, final stage), they can crawl about the host fish. It appears that they are most damaging to the host fish in these final, motile stages.
Sea lice have always been relatively common on adult salmon as they return to spawn. However, sea lice cannot tolerate [[fresh water]], and drop off the fish as they encounter reduced [[salinity|salinities]]. Natural infection dynamics on wild salmon are not well understood. However, lice are typically very rare on juvenile salmon in areas far from fish farms.
By contrast, relatively high abundances have repeatedly been reported on juvenile salmon that have migrated past fish farms. Evidence collected in both the [[Atlantic Ocean|Atlantic]] and [[Pacific Ocean]]s indicates that these infestation levels can often be lethal. Smaller host fish appear to be particularly vulnerable. Hence, [[pink salmon]] (''Oncorhynchus gorbuscha''), which migrate out to sea immediately upon emergence from spawning gravel, are particularly at risk. Nonetheless, larger species, specifically including wild [[Atlantic salmon]] (''Salmo salar'') have been found to have lethal lice loads near fish farms. Sea lice are also economically damaging to the fish farms themselves; in one recent year, sea lice cost salmon farmers more than [[United States dollar|US$]]100 million for treatment and lost production, which represents about 20% of their total costs.
Currently, fish farmers rely heavily on the chemical [[emamectin benzoate]] (SLICE) for controlling sea louse infestation rates. Many governments now impose limits on sea louse infestation levels on fish farms. The adequacy of existing regulations, and the environmental impacts of the use of SLICE are highly controversial. Public opinion is particularly polarized in the northeast Pacific where a [[moratorium]] on expansion has been lifted by the [[British Columbia]] government while the [[Alaska]] government is maintaining a total ban on salmon farming in its waters.
==References==
<references/>
*[http://www.pacificsalmonforum.ca/pdfs-all-docs/ScienceandSeaLiceFinalFeb22-08.pdf Science and Sea Lice: What Do We Know? (2008)]—An independent report on the science relating to sea lice in British Columbia published by [http://www.pacificsalmonforum.ca/ The BC Pacific Salmon Forum]
*{{cite news |url=http://www.sfu.ca/mediapr/news_releases/archives/news03060601.htm |title=Study provides first direct evidence sea lice kill young wild salmon |publisher=[[Simon Fraser University]] |year=2006}}
*{{cite web |url=http://www.sfu.ca/cstudies/science/sealice.htm |title=Wild salmon and sea lice |publisher=[[Simon Fraser University]]}}
*[http://www.watershed-watch.org/publications/index.html?cid=8 Watershed Watch]: an organisation that promotes salmon protection in British Columbia
{{fisheries and fishing}}
[[Category:Copepods]]
[[Category:Fish diseases]]
[[Category:Veterinary parasitology]]
[[Category:Aquaculture]]