View source for Sea louse

{{Short description|Family of copepods}}
{{for|the itching dermatitis referred to as "sea lice"|Seabather's eruption}}
{{Automatic taxobox
| name = Sea lice
| image = male female sea lice.jpg
| image_caption = Male and female ''[[Salmon louse|Lepeophtheirus salmonis]]''
| taxon = Caligidae
| authority = [[Hermann Burmeister|Burmeister]], 1834&nbsp;<ref name="Ahyong"/>
| subdivision_ranks = Genera&nbsp;<ref name="WoRMS">{{cite WoRMS |author=T. Chad Walter & Geoff Boxshall |title=Caligidae |year=2011 |db=Copepoda |id=135513 |access-date=January 12, 2012}}</ref>
| subdivision =
*''[[Abasia (genus)|Abasia]]'' <small>C. B. Wilson, 1908</small>
*''[[Alanlewisia]]'' <small>Boxshall, 2008</small>
*''[[Alebion (genus)|Alebion]]'' <small>Krøyer, 1863</small>
*''[[Alicaligus]]'' <small>Shiino, 1955</small>
*''[[Anchicaligus]]'' <small>Stebbing, 1900</small>
*''[[Anuretes]]'' <small>Heller, 1865</small>
*''[[Arrama]]'' <small>Dojiri & Cressey, 1991</small>
*''[[Avitocaligus]]'' <small>Boxshall & Justine, 2005</small>
*''[[Belizia]]'' <small>Cressey, 1990</small>
*''[[Caligodes]]'' <small>Heller, 1865</small>
*''[[Caligus]]'' <small>O. F. Müller, 1785</small>
*''[[Calistes]]'' <small>Dana, 1852</small>
*''[[Caritus]]'' <small>Cressey, 1967</small>
*''[[Cresseyella]]'' <small>Bezdek & Cressey, 2004</small>
*''[[Dartevellia]]'' <small>Brian, 1939</small>
*''[[Diphyllogaster]]'' <small>Brian, 1899</small>
*''[[Echetus (genus)|Echetus]]'' <small>Kroyer, 1863</small>
*''[[Euryphorus]]'' <small>H. Milne-Edwards, 1840</small>
*''[[Gloiopotes]]'' <small>Steenstrup & Lütken, 1861</small>
*''[[Hermilius]]'' <small>Heller, 1865</small>
*''[[Indocaligus]]'' <small>Pillai, 1961</small>
*''[[Kabataella]]'' <small>Prabha & Pillai, 1983</small>
*''[[Lepeophtheirus]]'' <small>von Nordmann, 1832</small>
*''[[Mappates]]'' <small>Rangnekar, 1958</small>
*''[[Markevichus]]'' <small>Özdikmen, 2008</small>
*''[[Paralebion]]'' <small>C. B. Wilson, 1911</small>
*''[[Parapetalus]]'' <small>Steenstrup & Lütken, 1861</small>
*''[[Parechetus]]'' <small>Pillai, 1962</small>
*''[[Pseudanuretes]]'' <small>[[Satyu Yamaguti|Yamaguti]], 1936</small>
*''[[Pseudechetus]]'' <small>Prabha & Pillai, 1979</small>
*''[[Pseudocaligus]]'' <small>A. Scott, 1901</small>
*''[[Pseudolepeophtheirus]]'' <small>Markevich, 1940</small>
*''[[Pupulina]]'' <small>Beneden, 1892</small>
*''[[Sciaenophilus]]'' <small>Beneden, 1852</small>
*''[[Synestius]]'' <small>Steenstrup & Lütken, 1861</small>
*''[[Tuxophorus]]'' <small>C. B. Wilson, 1908</small>
| synonyms = Euryphoridae
}}

'''Sea lice''' (singular: '''sea louse''') are [[copepod]]s (small [[crustacean]]s) of the family '''Caligidae''' within the order [[Siphonostomatoida]]. They are marine [[ectoparasite]]s (external parasites) that feed on the mucus, epidermal tissue, and blood of host fish. The roughly 559 species in 37 genera include around 162 ''[[Lepeophtheirus]]'' and 268 ''[[Caligus]]'' species.

The genera ''Lepeophtheirus'' and ''Caligus'' parasitize marine fish. ''[[Lepeophtheirus 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.

''Caligus rogercresseyi'' has become a major parasite of concern on [[Aquaculture of salmonids|salmon farms]] in countries including Chile<ref name="Bravo">{{cite journal |author=S. Bravo |year=2003 |title=Sea lice in Chilean salmon farms |journal=[[Bulletin of the European Association of Fish Pathologists]] |volume=23 |issue=4 |pages=197–200}}</ref> and Scotland.<ref>{{cite news| last=Ungoed-Thomas | first=Jon | title='Monstrous' sea lice and jellyfish invasions blighting Scottish salmon farms |newspaper=The Guardian | date=16 September 2023 | url=https://www.theguardian.com/environment/2023/sep/16/sea-lice-jellyfish-farmed-scottish-salmon-supermarkets}}</ref> Studies are under way to gain a better understanding of the parasite and the host-parasite interactions. Recent evidence is also emerging that ''L. salmonis'' in the Atlantic has sufficient genetic differences from ''L. salmonis'' from the Pacific to suggest that Atlantic and Pacific ''L. salmonis'' may have independently co-evolved with Atlantic and Pacific salmonids respectively.<ref>{{cite journal |author1=R. Yazawa |author2=M. Yasuike |author3=J. Leong |author4=K. R. von Schalburg |author5=G. A. Cooper |author6=M. Beetz-Sargent |author7=A. Robb |author8=W. S. Davidson |author9=S. R. Jones |author10=B. F. Koop |year=2008 |title=EST and mitochondrial DNA sequences support a distinct Pacific form of salmon louse, ''Lepeophtheirus salmonis'' |journal=Marine Biotechnology |volume=10 |issue=6 |pages=741–749 |doi=10.1007/s10126-008-9112-y |pmid=18574633|doi-access=free }}</ref>

==Diversity==
The family Caligidae is estimated to contain around 559 species in 37 genera.<ref name="Ahyong">{{cite book|author1=Shane T. Ahyong|author2=James K. Lowry|author3=Miguel Alonso|author4=Roger N. Bamber|author5=Geoffrey A. Boxshall|author6=Peter Castro|author7=Sarah Gerken|author8=Gordan S. Karaman|author9=Joseph W. Goy|author10=Diana S. Jones|author11=Kenneth Meland|author12=D. Christopher Rogers|author13=Jörundur Svavarsson|year=2011|chapter=Subphylum Crustacea Brünnich, 1772|editor=Z.-Q. Zhang|title=Animal biodiversity: an outline of higher-level classification and survey of taxonomic richness|publisher=Zootaxa|volume=3148|pages=165–191|chapter-url=http://www.mapress.com/zootaxa/2011/f/zt03148p191.pdf
}}</ref> The largest of these are ''[[Caligus]]'', with around 268 species,<ref>{{cite WoRMS |author=Geoff Boxshall |year=2011 |title=''Caligus'' O.F. Müller, 1785 |db=Copepoda |id=135566 |access-date=January 12, 2012}}</ref> and ''[[Lepeophtheirus]]'' with around 162 species.<ref>{{cite WoRMS |author=T. Chad Walter & Geoff Boxshall |year=2011 |title=''Lepeophtheirus'' von Nordmann, 1832 |db=Copepoda |id=135568 |access-date=January 12, 2012}}</ref>

==Wild fish==
Most understanding of the biology of sea lice, other than the early morphological studies, is based on laboratory studies designed to understand issues associated with sea lice infecting fish on salmon farms. Information on sea lice biology and interactions with [[wild fish]] is sparse in most areas with a long-term history of open net-cage development, since understanding background levels of sea lice and transfer mechanisms has rarely been a condition of tenure license for farm operators.

Many sea louse species are specific with regard to host genera, for example ''L. salmonis'', which has high specificity for [[Fish migration #Anadromous|anadromous]] fish including sticklebacks and [[salmonid]]s including the widely farmed [[Atlantic salmon]] (''Salmo salar''). ''Lepeophtheirus salmonis'' can parasitize other salmonids to varying degrees, including [[brown trout]] ([[sea trout]]: ''Salmo trutta''), [[Arctic char]] (''Salvelinus alpinus''), and all species of Pacific salmon. In the case of Pacific salmon, [[coho]], [[Chum salmon|chum]], and [[pink salmon]] (''Oncorhynchus kisutch'', ''O. keta'', and ''O. gorbuscha'', respectively) mount strong tissue responses to attaching ''L. salmonis'', which lead to rejection within the first week of infection.<ref name=Wagner>{{cite journal |author1=G. N. Wagner |author2=M. D. Fast |author3=S. C. Johnson |year=2008 |title=Physiology and immunology of ''Lepeophtheirus salmonis'' infections of salmonids |journal=[[Trends in Parasitology]] |volume=24 |pages=176–183 |doi=10.1016/j.pt.2007.12.010 |pmid=18329341 |issue=4}}</ref> Pacific ''L. salmonis'' can also develop, but not complete, its full lifecycle on the [[three-spined stickleback]] (''Gasterosteus aculeatus'').<ref>{{cite journal |author1=S. R. M. Jones |author2=G. Prosperi-Porta |author3=E. Kim |author4=P. Callow |author5=N. B. Hargreaves |year=2006 |title=The occurrence of ''Lepeophtheirus salmonis'' and ''Caligus clemensi'' (Copepoda: Caligidae) on threespine stickleback ''Gasterosteus aculeatus'' in coastal British Columbia |journal=[[Journal of Parasitology]] |volume=92 |issue=3 |pages=473–480 |pmid=16883988 |doi=10.1645/GE-685R1.1|s2cid=41370981 }}</ref> This has not been observed with Atlantic ''L. salmonis''.

How [[planktonic]] stages of sea lice disperse and find new hosts is still not completely known. Temperature, light, and currents are major factors and survival depends on salinity above 25&nbsp;[[per mil|‰]].<ref>{{cite journal |author1=M. Costelloe |author2=J. Costelloe |author3=G. O'Donohoe |author4=N. J. Coghlan |author5=M. Oonk |author6=Y. van der Heijden |year=1998 |title=Planktonic distribution of sea lice larvae ''Lepeophtheirus salmonis'', in Killary Harbour, west coast of Ireland |journal=[[Journal of the Marine Biological Association of the United Kingdom]] |volume=78 |pages=853–874 |url=http://filaman.ifm-geomar.de/ICES_Documents/ICES_Documents2002/T/T0602.PDF |doi=10.1017/S0025315400044830 |issue=3|s2cid=85050780 }}</ref><ref name=Genna>{{cite journal |author1=R. L. Genna |author2=W. Mordue |author3=A. W. Pike |author4=A. J. Mordue-Luntz |year=2005 |title=Light intensity, salinity, and host velocity influence presettlement intensity and distribution on hosts by copepodids of sea lice, ''Lepeophtheirus salmonis'' |journal=[[Canadian Journal of Fisheries and Aquatic Sciences]] |volume=62 |pages=2675–2682 |doi=10.1139/f05-163 |issue=12|s2cid=84155984 }}</ref><ref name=Costello>{{cite journal |author=M. J. Costello |year=2006 |title=Ecology of sea lice parasitic on farmed and wild fish |journal=[[Trends in Parasitology]] |volume=22 |pages=475–483 |url=http://ec.europa.eu/fisheries/partners/consultations/aquaculture/contributions/2006_sea_lice_ecology_paper.pdf |doi=10.1016/j.pt.2006.08.006 |pmid=16920027 |issue=10}}</ref><ref>{{cite journal |author=Kenneth M. Brooks |year=2005 |title=The effects of water temperature, salinity, and currents on the survival and distribution of the infective copepodid stage of sea lice (''Lepeophtheirus salmonis'') originating on Atlantic salmon farms in the Broughton Archipelago of British Columbia, Canada |journal=[[Reviews in Fisheries Science]] |volume=13 |pages=177–204 |doi=10.1080/10641260500207109 |issue=3|s2cid=84252746 }}</ref> ''L. salmonis'' copepodids migrating upwards towards light and salmon [[Juvenile salmon|smolt]] moving downwards at daybreak have been hypothesized to facilitate finding a host.<ref name=Heuch>{{cite journal |doi=10.1139/f95-069 |author1=P. A. Heuch |author2=A. Parsons |author3=K. Boxaspen |year=1995 |title=Diel vertical migration: a possible host finding mechanism in salmon lice (''Lepeophtheirus salmonis'') copepodid? |journal=[[Canadian Journal of Fisheries and Aquatic Sciences]] |volume=52 |pages=681–689 |issue=4}}</ref> Several field and modeling studies on ''L. salmonis'' have examined copepodid populations and have shown that planktonic stages can be transported tens of kilometres from their source,<ref name=Costello/><ref>{{cite journal |author1=M. A. McKibben |author2=D. W. Hay |year=2004 |title=Distributions of planktonic sea lice larvae ''Lepeophtheirus salmonis'' in the inter-tidal zone in Loch Torrindon, western Scotland in relation to salmon farm production cycles |journal=[[Aquaculture Research]] |volume=35 |pages=742–750 |doi=10.1111/j.1365-2109.2004.01096.x |issue=8}}</ref> including how their behaviour results in their being moved towards the coastline and mouth of estuaries.<ref name="pmid19586950">{{cite journal |author=M. J. Costello |year=2009 |title=How sea lice from salmon farms may cause wild salmonid declines in Europe and North America and be a threat to fishes elsewhere |journal=[[Proceedings of the Royal Society B]] |volume=276 |pages=3385–3394 |doi=10.1098/rspb.2009.0771 |pmid=19586950 |issue=1672 |pmc=2817184}}</ref>

The source of ''L. salmonis'' infections when salmon return from fresh water has always been a mystery. Sea lice die and fall off [[anadromous]] fish such as salmonids when they return to fresh water. Atlantic salmon return and travel upstream in the fall to reproduce, while the smolts do not return to salt water until the next spring. Pacific salmon return to the marine nearshore starting in June, and finish as late as December, dependent upon species and run timing, whereas the smolts typically outmigrate starting in April, and ending in late August, dependent upon species and run timing.

Sea lice possibly survive on fish that remain in the estuaries or they transfer to an as yet unknown alternate host to spend the winter. Smolt get infected with sea lice larvae, or even possibly adults, when they enter the estuaries in the spring. How sea lice distribute between fish in the wild also is not known. Adult stages of ''Lepeophtheirus'' spp. can transfer under laboratory conditions, but the frequency is low. ''Caligus'' spp. transfer quite readily and between different species of fish, and are regularly found in the plankton.<ref name=Costello />

==Morphology==
''L. salmonis'' tends to be about twice the size of most ''Caligus'' spp. (e.g. ''C. elongatus'', ''C. clemensi'', etc.). The body consists of four regions: [[cephalothorax]], fourth (leg-bearing) segment, genital complex, and abdomen.<ref name="Johnson, S.C. 1991">{{cite journal |author1=S. C. Johnson |author2=L. J. Albright |year=1991 |title=The developmental stages of ''Lepeophtheirus salmonis'' (Krøyer, 1837) (Copepoda: Caligidae) |journal=[[Canadian Journal of Zoology]] |volume=69 |issue=4 |pages=929–950 |doi=10.1139/z91-138}}</ref> The cephalothorax forms a broad shield that includes all of the body segments up to the third leg-bearing segment. It acts like a suction cup in holding the louse on the fish. All species have mouth parts shaped as a siphon or oral cone (characteristic of the Siphonostomatoida). The second [[antennae (biology)|antennae]] and oral appendages are modified to assist in holding the parasite on the fish. The second pair of antennae is also used by males to grasp the female during copulation.<ref name="Anstensrud, M 1990">{{cite journal |author=M. Anstensrud |year=1990 |title=Moulting and mating in ''Lepeophtheirus pectoralis'' (Copepoda: Caligidae) |journal=[[Journal of the Marine Biological Association of the United Kingdom]] |volume=70 |pages=269–281 |doi=10.1017/S0025315400035396 |issue=2|s2cid=86201794 }}</ref> The adult females are always significantly larger than males and develop a very large genital complex, which in many species makes up the majority of the body mass. Two egg strings of 500 to 1000 eggs (''L. salmonis''), which darken with maturation, are roughly the same length as the female's body. One female can produce 6–11 pairs of egg strings in a lifetime around seven months.<ref name=Costello/><ref name=Heuch/><ref>{{cite journal |author1=A. Mustafa |author2=G. A. Conboy |author3=J. F. Burka |year=2001 |title=Life-span and reproductive capacity of sea lice, ''Lepeophtheirus salmonis'', under laboratory conditions |journal=Aquaculture Association of Canada Special Publication |volume=4 |pages=113–114}}</ref>

==Development==

Sea lice have both free-swimming (planktonic) and parasitic life stages, all separated by moults.<ref name="Johnson, S.C. 1991"/><ref name="Anstensrud, M 1990"/><ref name=Schram>{{cite book |author=Thomas A. Schram |year=1993 |chapter=Supplementary description of the developmental stages of ''Lepeophtheirus salmonis'' (Krøyer, 1837) (Copepoda: Caligidae) |title=Pathogens of Wild and Farmed Fish: Sea Lice |editor1=G. A. Boxshall |editor2=D. Defaye |publisher=[[Ellis Horwood]] |location=[[Chichester]] |isbn=978-0-13-015504-7 |pages=30–50 |chapter-url=https://books.google.com/books?id=N5C6hoemktcC&pg=PA30}}</ref><ref name=Pike>{{cite book |author1=A. W. Pike |author2=S. L. Wadsworth |year=1999 |title=Sealice on salmonids: their biology and control |journal=[[Advances in Parasitology]] |volume=44 |pages=233–337 |pmid=10563397 |doi=10.1016/S0065-308X(08)60233-X |isbn=978-0-12-031744-8}}</ref> The development rate for ''L. salmonis'' from egg to adult varies from 17 to 72 days depending on temperature. The lifecycle of ''L. salmonis'' is shown in the figure; the sketches of the stages are from Schram.<ref name=Schram/>

Eggs hatch into [[Nauplius (larva)|nauplii]] I, which moult to a second naupliar stage; neither naupliar stage feeds, depending on yolk reserves for energy, and both are adapted for swimming. The copepodid stage is the infectious stage and it searches for an appropriate host, likely by chemo- and mechanosensory clues. Currents, salinity, light, and other factors also assist copepodids in finding a host.<ref name=Costello/> Preferred settlement on the fish occurs in areas with the least hydrodynamic disturbance, particularly the fins and other protected areas.<ref name=Genna/><ref>{{cite journal |author1=J. E. Bron |author2=C. Sommerville |author3=M. Jones |author4=G. H. Rae |year=1991 |title=The settlement and attachment of early stages of the salmon louse, ''Lepeophtheirus salmonis'' (Copepoda: Caligidae) on the salmon host ''Salmo salar'' |journal=[[Journal of Zoology]] |volume=224 |issue=2 |pages=201–212 |doi=10.1111/j.1469-7998.1991.tb04799.x}}</ref> Once attached to a suitable host, copepods feed for a period of time prior to moulting to the chalimus I stage. Sea lice continue their development through three additional chalimus stages each separated by a moult. A characteristic feature of all four chalimus stages is that they are physically attached to the host by a structure referred to as the frontal filament. Differences in the timing, method of production, and the physical structure of the frontal filament are seen between different species of sea lice. With exception of a short period during the moult, the preadult and adult stages are mobile on the fish, and in some cases, can move between host fish. Adult females, being larger, occupy relatively flat body surfaces on the posterior ventral and dorsal midlines and may actually outcompete preadults and males at these sites.<ref>{{cite journal |author1=C. D. Todd |author2=A. M. Walker |author3=J. E. Hoyle |author4=S. J. Northcott |author5=A. F. Walker |author6=M. G. Ritchie |year=2000 |title=Infestations of wild adult Atlantic salmon (''Salmo salar'' L.) by the ectoparasitic copepod sea louse ''Lepeophtheirus salmonis'' (Krøyer): prevalence, intensity and the spatial distribution of males and females on the host fish |journal=[[Hydrobiologia]] |volume=429 |issue=2–3 |pages=181–196 |doi=10.1023/A:1004031318505|s2cid=31842097 }}</ref>

==Feeding habits==
Until they locate a host, the naupliar and copepodid stages are non-feeding and live on endogenous food stores. Once attached to the host, the copepodid stage begins feeding and begins to develop into the first chalimus stage. Copepods and chalimus stages have a developed gastrointestinal tract and feed on host mucus and tissues within range of their attachment. Pre-adult and adult sea lice, especially pregnant females, are aggressive feeders, in some cases feeding on blood in addition to tissue and mucus. Blood is often seen in the digestive tract, especially of adult females. ''L. salmonis'' is known to secrete large amounts of [[trypsin]] into its host's mucus, which may assist in feeding and digestion.<ref name=Wagner/><ref>{{cite journal |author1=Kara J. Firth |author2=Stewart C. Johnson |author3=Neil W. Ross |year=2000 |title=Characterization of proteases in the skin mucus of Atlantic salmon (''Salmo salar'') infected with the salmon louse (''Lepeophtheirus salmonis'') and in whole-body louse homogenates |journal=[[Journal of Parasitology]] |volume=86 |issue=6 |pages=1199–1205 |pmid=11191891 |jstor=3285000 |doi=10.1645/0022-3395(2000)086[1199:COPITS]2.0.CO;2|s2cid=8275088 }}</ref> Other compounds such as, [[prostaglandin E2]], have also been identified in ''L. salmonis'' secretions and may assist in feeding and/or serve the parasite in avoiding the immune response of the host by regulating it at the feeding site.<ref name=Wagner/><ref>{{cite journal |author1=M. D. Fast |author2=N. W. Ross |author3=S. C. Johnson |year=2005 |title=Prostaglandin E2 modulation of gene expression in an Atlantic salmon (''Salmo salar'') macrophage-like cell line (SHK-1) |journal=[[Developmental & Comparative Immunology]] |volume=29 |issue=11 |pages=951–963 |pmid=15936074 |doi=10.1016/j.dci.2005.03.007}}</ref> Whether sea lice are vectors of disease is unknown, but they can be carriers of bacteria and viruses likely obtained from their attachment to and feeding on tissues of contaminated fish.<ref>{{cite journal |author1=A. Nylund |author2=B. Bjørknes |author3=C. Wallace |year=1991 |title=''Lepeophtheirus salmonis'' – a possible vector in the spread of diseases on salmonids |journal=[[Bulletin of the European Association of Fish Pathologists]] |volume=11 |issue=6 |pages=213–216}}</ref>

==Disease==

===Pathology===
[[File:sea lice on salmon.jpg|thumb|Pregnant female ''[[Lepeophtheirus salmonis]]'' on Atlantic salmon, ''Salmo salar'']]
Sea lice cause physical and enzymatic damage at their sites of attachment and feeding, which results in abrasion-like lesions that vary in their nature and severity depending upon a number of factors, including host species, age, and general health of the fish. Whether stressed fish are particularly prone to infestation is unclear. Sea-lice infection causes a generalized [[chronic stress]] response in fish since feeding and attachment cause changes in the mucus consistency and damage the epithelium resulting in loss of blood and fluids, [[electrolyte]] changes, and [[cortisol]] release. This can decrease salmon immune responses and make them susceptible to other diseases and reduce growth and performance.<ref>{{cite journal |doi=10.3354/dao014195 |author1=S. C. Johnson |author2=L. J. Albright |year=1992 |title=Effects of cortisol implants on the susceptibility and the histopathology of the responses of naive coho salmon ''Oncorhynchus kisutch'' to experimental infection with ''Lepeophtheirus salmonis'' (Copepoda : Caligidae) |journal=[[Diseases of Aquatic Organisms]] |volume=14 |pages=195–205|doi-access=free }}</ref><ref>{{cite journal |doi=10.3354/dao041043 |author1=N. W. Ross |author2=K. J. Firth |author3=A. Wang |author4=J. F. Burka |author5=S. C. Johnson |year=2000 |title=Changes in hydrolytic enzyme activities of naive Atlantic salmon (''Salmo salar'') skin mucus due to infection with the salmon louse (''Lepeophtheirus salmonis'') and cortisol implantation |journal=[[Diseases of Aquatic Organisms]] |volume=41 |issue=1 |pages=43–51 |pmid=10907138|doi-access=free }}</ref>

The degree of damage is also dependent on the species of sea lice, the developmental stages that are present, and the number of sea lice on a fish. Little evidence exists of host tissue responses in Atlantic salmon at the sites of feeding and attachment, regardless of the development stage. In contrast, coho and pink salmon show strong tissue responses to ''L. salmonis'' characterized by epithelial [[hyperplasia]] and [[inflammation]]. This results in rejection of the parasite within the first week of infection in these species of salmonids.<ref name=Wagner/> Heavy infections of farmed Atlantic salmon and wild [[sockeye salmon]] (''Oncorhynchus nerka'') by ''L. salmonis'' can lead to deep lesions, particularly on the head region, even exposing the skull.

===Interactions between wild and farmed fish===
Some evidence indicates that sea lice flourishing on salmon farms can spread to nearby wild juvenile salmon and devastate these populations.<ref name="Krkosek_Science">{{cite journal |author1=M. Krkosek |author2=J. S. Ford |author3=A. Morton |author4=S. Lele |author5=R. A. Myers |author6=M. A. Lewis |year=2007 |title=Declining wild salmon populations in relation to parasites from farm salmon |journal=[[Science (journal)|Science]] |volume=318 |issue=5857 |pages=1772–5 |doi=10.1126/science.1148744 |pmid=18079401|bibcode=2007Sci...318.1772K |s2cid=86544687 }}</ref> 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.<ref name="Bravo"/><ref>{{cite web |url=http://www.farmedanddangerous.org/uploads/File/Reports/SeaLice_FullReport.pdf |title=Sea lice and salmon: elevating the dialogue on the farmed-wild salmon story |publisher=Watershed Watch Salmon Society |year=2004 |access-date=January 15, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20101214173552/http://farmedanddangerous.org/uploads/File/Reports/SeaLice_FullReport.pdf |archive-date=December 14, 2010 }}</ref> 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.<ref>{{cite journal |author1=A. Morton |author2=R. Routledge |author3=C. Peet |author4=A. Ladwig |year=2004 |title=Sea lice (''Lepeophtheirus salmonis'') infection rates on juvenile pink (''Oncorhynchus gorbuscha'') and chum (''Oncorhynchus keta'') salmon in the nearshore marine environment of British Columbia, Canada |journal=[[Canadian Journal of Fisheries and Aquatic Sciences]] |volume=61 |issue=2 |pages=147–157 |doi=10.1139/f04-016}}</ref><ref>{{cite thesis |author=Corey Ryan Peet |year=2007 |publisher=[[University of Victoria]] |degree=[[Master of Science|M.Sc.]] |title=Interactions between sea lice (''Lepeoptheirus salmonis'' and ''Caligus clemensii''), juvenile salmon (''Oncorhynchus keta'' and ''Oncorhynchus gorbuscha'') and salmon farms in British Columbia |hdl=1828/2346 }}</ref><ref>{{cite journal |author1=M. Krkošek |author2=A. Gottesfeld |author3=B. Proctor |author4=D. Rolston |author5=C. Carr-Harris |author6=M. A. Lewis |year=2007 |title=Effects of host migration, diversity and aquaculture on sea lice threats to Pacific salmon populations |journal=[[Proceedings of the Royal Society B]] |volume=274 |issue=1629 |pages=3141–3149 |pmid=17939989 |doi=10.1098/rspb.2007.1122 |pmc=2293942}}</ref> 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 <ref>{{cite journal |author1=A. Morton |author2=R. Routledge |author3=M. Krkošek |year=2008 |title=Sea louse infestation in wild juvenile salmon and Pacific herring associated with fish farms off the east-central coast of Vancouver Island, British Columbia |journal=North American Journal of Fisheries Management |volume=28 |pages=523–532 |doi=10.1577/M07-042.1 |issue=2 }}</ref><ref name="Krkosek_PNAS">{{cite journal |author1=M. Krkošek |author2=M. A. Lewis |author3=A. Morton |author4=L. N. Frazer |author5=J. P. Volpe |year=2006 |title=Epizootics of wild fish induced by farm fish |journal=[[Proceedings of the National Academy of Sciences]] |volume=103 |issue=42 |pages=15506–15510 |pmid=17021017 |pmc=1591297 |doi=10.1073/pnas.0603525103|doi-access=free }}</ref> Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable. Sea trout populations in recent years may have seriously declined due to infestation by sea lice,<ref>{{cite book |author=Charles Clover |year=2004 |title=The End of the Line: How Overfishing is Changing the World and What We Eat |publisher=[[Ebury Press]] |location=London |isbn=978-0-09-189780-2}}</ref> and Krkosek ''et al.'' have claimed that on the [[Pacific coast of Canada]] the louse-induced mortality of pink salmon in some regions is over 80%.<ref name="Krkosek_Science"/> A few studies indicated no long-term damage to fish stocks in some locations,<ref>{{cite journal |author1=S. R. M. Jones |author2=N. B. Hargreaves |year=2009 |title=Infection threshold to estimate ''Lepeophtheirus salmonis''-associated mortality among juvenile pink salmon |journal=[[Diseases of Aquatic Organisms]] |volume=84 |issue=2 |pages=131–137 |pmid=19476283 |doi=10.3354/dao02043|doi-access=free}}</ref> and a population decline in wild salmon that occurred in 2002 was caused by "something other than sea lice".<ref>{{cite journal |author1=Gary D. Marty |author2=S. M. Saksida |author3=T. J. Quinn II |year=2010 |title=Relationship of farm salmon, sea lice, and wild salmon populations |journal=[[Proceedings of the National Academy of Sciences]] |volume=107 |issue=52 |pages=22599–22604 |doi=10.1073/pnas.1009573108 |doi-access=free|pmid=21149706 |pmc=3012511|bibcode=2010PNAS..10722599M }}</ref> However, the repeated epizootics of lice on wild fish have only occurred in areas with salmon farms in Ireland, Britain (Scotland), Norway, Canada (British Columbia), and Chile.<ref name="Costello JFD">{{cite journal |author=M. J. Costello |year=2009 |title=The global economic cost of sea lice to the salmonid farming industry |journal=[[Journal of Fish Diseases]] |volume=32 |issue=1 |pages=115–118 |doi=10.1111/j.1365-2761.2008.01011.x|pmid=19245636 |s2cid=9837376 }}</ref> Field sampling of copepodids, and hydrographic and population models, show how ''L. salmonis'' from farms can cause mass infestations of seaward-migrating salmonids, and this effect can occur up to {{convert|30|km|abbr=on}} from the farms.<ref name="pmid19586950" />

Several scientific studies have suggested that [[Aquaculture of salmon#Sea cages|caged, farmed salmon]] harbour lice to a degree that can destroy surrounding wild salmon populations.<ref name="Krkosek_PNAS"/> Other studies have shown that lice from farmed fish have relatively no effect on wild fish if good husbandry and adequate control measures are carried out (see section: Control on salmon farms).<ref name=Heuch05>{{cite journal |author1=Peter Andreas Heuch |author2=Pål Arne Bjørn |author3=Bengt Finstad |author4=Jens Christian Holst |author5=Lars Asplin |author6=Frank Nilsen |year=2005 |title=A review of the Norwegian 'National Action Plan Against Salmon Lice on Salmonids': The effect on wild salmonids |journal=[[Aquaculture (journal)|Aquaculture]] |volume=246 |issue=1–4 |pages=79–92 |doi=10.1016/j.aquaculture.2004.12.027}}</ref> Further studies to establish wild-farmed fish interactions are ongoing, particularly in Canada, Britain (Scotland), Ireland, and Norway. A reference manual with protocol and guidelines for studying wild/cultured fish interactions with sea lice has been published.<ref>{{cite web |url=http://www.pacificsalmonforum.ca/wild/index.php |title=Protocols and Guidelines: A Reference Manual for Research Involving Wild/Cultured Fish Interactions with Sea Lice |publisher=[[Pacific Salmon Forum]] |access-date=September 17, 2009}}</ref>

==Fish farming==

===Control on salmon farms===
This has been reviewed by Pike & Wadsworth,<ref name=Pike/> McVicar,<ref>{{cite journal |author=Alasdair H. McVicar |year=2004 |title=Management actions in relation to the controversy about salmon lice infections in fish farms as a hazard to wild salmonid populations |journal=[[Aquaculture Research]] |volume=35 |issue=8 |pages=751–758 |doi=10.1111/j.1365-2109.2004.01097.x|doi-access=free }}</ref> and Costello.<ref name=Costello/> Integrated pest management programs for sea lice are instituted or recommended in a number of countries, including Canada,<ref>{{cite book |url=http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_fact-fiche/over-lice-apercu-pou/index-eng.php |title=Integrated Pest Management of Sea Lice in Salmon Aquaculture |year=2003 |isbn=978-0-662-34002-7 |access-date=March 26, 2010|publisher=[[Health Canada]]}}</ref><ref>{{cite web |url=http://www.al.gov.bc.ca/ahc/fish_health/SL%20Mgmnt%20Strat%202007%202008%20Final.pdf |title=Sea Lice Management Strategy 2007/2008 |access-date=September 11, 2009 |publisher=[[British Columbia Ministry of Agriculture and Lands]]}}</ref> Norway,<ref name=Heuch05/> Scotland,<ref>{{cite journal |author1=A. J. Rosie |author2=P. T. R. Singleton |year=2002 |title=Discharge consents in Scotland |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=616–621 |doi=10.1002/ps.475|pmid=12138628 }}</ref> and Ireland.<ref>{{cite journal |author=B. Grist |year=2002 |title=The regulatory system for aquaculture in the Republic of Ireland |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=609–615 |doi=10.1002/ps.512 |pmid=12138627}}</ref> Identification of epidemiological factors as potential [[risk factor]]s for sea lice abundance<ref>{{cite journal |doi=10.3354/dao057085 |author1=C. W. Revie |author2=G. Getinby |author3=J. W. Treasurer |author4=C. Wallace |year=2003 |title=Identifying epidemiological factors affecting sea lice ''Lepeophtheirus salmonis'' abundance on Scottish salmon farms using general linear models |journal=[[Diseases of Aquatic Organisms]] |volume=57 |issue=1–2 |pages=85–95 |pmid=14735925|doi-access=free }}</ref> with effective sea lice monitoring programs have been shown to effectively reduce sea lice levels on salmon farms.<ref>{{cite journal |author1=S. Saksida |author2=G. A. Karreman |author3=J. Constantine |author4=A. Donald |year=2007 |title=Differences in ''Lepeophtheirus salmonis'' abundance levels on Atlantic salmon farms in the Broughton Archipelago, British Columbia, Canada |journal=[[Journal of Fish Diseases]] |volume=30 |issue= 6|pages=357–366 |doi=10.1111/j.1365-2761.2007.00814.x |pmid=17498179}}</ref>

====Natural predators====
[[Cleaner fish]], including five species of [[wrasse]] (Labridae), are used on [[fish farms]] in Norway and to a lesser extent in Scotland, Shetland and Ireland.<ref>{{cite journal |author=James W. Treasurer |year=2002 |title=A review of potential pathogens of sea lice and the application of cleaner fish in biological control |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=546–558 |pmid=12138621 |doi=10.1002/ps.509}}</ref> Their potential has not been researched in other fish farming regions, such as Pacific and Atlantic Canada or Chile.

====Husbandry====
Good husbandry techniques include fallowing, removal of dead and sick fish, prevention of net fouling, etc. Bay management plans are in place in most fish farming regions to keep sea lice below a level that could lead to health concerns on the farm or affect wild fish in surrounding waters. These include separation of year classes, counting and recording of sea lice on a prescribed basis, use of parasiticides when sea lice counts increase, and monitoring for resistance to parasiticides.

====Salmon breeding====
Early findings suggested genetic variation in the susceptibility of Atlantic salmon to ''Caligus elongatus''.<ref>{{cite journal |doi=10.1139/cjz-77-8-1332 |author1=A. Mustafa |author2=B. M. MacKinnon |year=1999 |title=Genetic variation in susceptibility of Atlantic salmon to the sea louse ''Caligus elongatus'' Nordmann 1882 |journal=[[Canadian Journal of Zoology]] |volume=77 |pages=1332–1335 |issue=8}}</ref> Research then began to identify trait markers,<ref>{{cite journal |author1=Catherine S. Jones |author2=Anne E. Lockyer |author3=Eric Verspoor |author4=Christopher J. Secombes |author5=Leslie R. Noble |year=2002 |title=Towards selective breeding of Atlantic salmon for sea louse resistance: approaches to identify trait markers |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=559–568 |pmid=12138622 |doi=10.1002/ps.511}}</ref> and recent studies have shown that susceptibility of Atlantic salmon to ''L. salmonis'' can be identified to specific families and that there is a link between [[MHC Class II]] and susceptibility to lice.<ref>{{cite journal |doi=10.3354/dao076057 |author1=K. A. Glover |author2=U. Grimholt |author3=H. G. Bakke |author4=F. Nilsen |author5=A. Storset |author6=Ø. Skaala |year=2007 |title=Major histocompatibility complex (MHC) variation and susceptibility to the sea louse ''Lepeophtheirus salmonis'' in Atlantic salmon ''Salmo salar'' |journal=[[Diseases of Aquatic Organisms]] |volume=76 |issue=1 |pages=57–66 |pmid=17718166|doi-access=free |hdl=11250/108858 |hdl-access=free }}</ref>

In October 2012, the grocery chain Sobeys pulled whole Atlantic salmon from 84 store locations in the Canadian Maritimes after concerns were raised over sea lice.
<ref>{{Cite web | url=http://www.cbc.ca/newsblogs/yourcommunity/2012/10/grocery-chain-pulls-whole-salmon-following-facebook-posts.html | title=Grocery chain pulls whole salmon following Facebook posts - Your Community}}</ref>

In 2017, salmon prices in Norway increased by 15% over a 3-month period because of a sea lice outbreak.
<ref>{{Cite web | url=https://www.foxnews.com/food-drink/sea-lice-outbreak-sends-salmon-prices-soaring | title=Sea lice outbreak sends salmon prices soaring| website=[[Fox News]]| date=2017-01-24}}</ref>

== Treatments ==

=== Freshwater ===
Freshwater is sometimes adequate to kill the sea lice and as salmon eventually swim in fresh water, they are not harmed.<ref>{{cite news |title=Ship that can wash sea lice from farmed salmon now on Vancouver Island |url=https://vancouverisland.ctvnews.ca/ship-that-can-wash-sea-lice-from-farmed-salmon-now-on-vancouver-island-1.4391217 |access-date=25 April 2019 |work=[[CTV News]] |agency=[[The Canadian Press]] |date=23 April 2019}}</ref>

===Drugs and vaccines===
The range of therapeutants for farmed fish was limited, often due to regulatory processing limitations. All drugs used have been assessed for environmental impact and risks.<ref name=Burridge>{{cite journal |author=L. E. Burridge |year=2003 |title=Chemical use in marine finfish aquaculture in Canada: A review of current practices and possible environmental effects |journal=[[Canadian Technical Reports of Fisheries and Aquatic Sciences]] |volume=2450 |pages=97–131}}</ref><ref>{{cite book |author1=K. Haya |author2=L. E. Burridge |author3=I. M. Davies |author4=E. Ervik |year=2005 |title=A review and assessment of environmental risk of chemicals used for the treatment of sea lice infestations of cultured salmon |volume=5 |issue=M |pages=305–340 |doi=10.1007/b136016 |series=Handbook of Environmental Chemistry |isbn=978-3-540-25269-6}}</ref> The parasiticides are classified into bath and in-feed treatments as follows:

====Bath treatments====
There are both advantages and disadvantages to using bath treatments. Bath treatments are more difficult and need more manpower to administer, requiring skirts or tarpaulins to be placed around the cages to contain the drug. Prevention of reinfection is a challenge since it is practically impossible to treat an entire bay in a short time period. Since the volume of water is imprecise, the required concentration is not guaranteed. Crowding of fish to reduce the volume of drug can also stress the fish. Recent use of well-boats containing the drugs has reduced both the concentration and environmental concerns, although transferring fish to the well boat and back to the cage can be stressful. The major advantage to bath treatments is that all the fish will be treated equally, in contrast to in-feed treatments where amount of drug ingested can vary due to a number of reasons.

====Organophosphates====
[[Organophosphates]] are [[acetylcholinesterase inhibitors]] and cause excitatory paralysis leading to death of sea lice when given as a bath treatment. [[Dichlorvos]] was used for many years in Europe and later replaced by [[azamethiphos]], the active ingredient in Salmosan, which is safer for operators to handle.<ref>{{cite journal |author1=I. Denholm |author2=G. J. Devine |author3=T. E. Horsberg |author4=S. Sevatdal |author5=A. Fallang |author6=D. V. Nolan |author7=R. Powell |year=2002 |title=Analysis and management of resistance to chemotherapeutants in salmon lice ''Lepeophtheirus salmonis'' (Copepoda: Caligidae) |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=528–536 |pmid=12138619 |doi=10.1002/ps.482}}</ref> Azamethiphos is water-soluble and broken down relatively quickly in the environment. Resistance to organophosphates began to develop in Norway in the mid 1990s, apparently due to acetylcholinesterases being altered due to mutation.<ref>{{cite journal |doi=10.1002/ps.932 |author1=Anders Fallang |author2=Jennifer Mara Ramsay |author3=Sigmund Sevatdal |author4=John F. Burka |author5=Philip Jewess |author6=K. Larry Hammell |author7=Tor E. Horsberg |year=2004 |title=Evidence for occurrence of an organophosphate-resistant type of acetylcholinesterase in strains of sea lice (''Lepeophtheirus salmonis'' Krøyer) |journal=[[Pest Management Science]] |volume=60 |issue=12 |pages=1163–1170 |pmid=15578596}}</ref> Use has declined considerably with the introduction of SLICE, [[emamectin benzoate]].

====Pyrethroids====
[[Pyrethroids]] are direct stimulators of sodium channels in neuronal cells, inducing rapid depolarization and spastic paralysis leading to death. The effect is specific to the parasite since the drugs used are only slowly absorbed by the host and rapidly metabolized once absorbed. [[Cypermethrin]] (Excis, Betamax) and [[deltamethrin]] (Alphamax) are the two pyrethroids commonly used to control sea lice. Resistance to pyrethroids has been reported in Norway and appears to be due to a mutation leading to a structural change in the sodium channel which prevents pyrethroids from activating the channel.<ref>{{cite journal |doi=10.3354/dao065129 |author1=A. Fallang |author2=I. Denholm |author3=T. E. Horsberg |author4=M. S. Williamson |year=2005 |title=Novel point mutation in the sodium channel gene of pyrethroid-resistant sea lice ''Lepeophtheirus salmonis'' (Crustacea: Copepoda) |journal=[[Diseases of Aquatic Organisms]] |volume=65 |issue=2 |pages=129–136 |pmid=16060266|doi-access=free }}</ref> Use of deltamethrin has been increasing as an alternate treatment with the rise in resistance observed with emamectin benzoate.

====Topical disinfectants====
Bathing fish with [[hydrogen peroxide]] (350–500&nbsp;mg/L for 20&nbsp;min) will remove mobile sea lice from fish. It is environmentally friendly since H<sub>2</sub>O<sub>2</sub> dissociates to water and oxygen, but can be toxic to fish, depending on water temperature, as well as to operators.<ref>{{cite journal |author=A. N. Grant |year=2002 |title=Medicines for sea lice |journal=[[Pest Management Science]] |volume=58 |issue=6 |pages=521–527 |pmid=12138618 |doi=10.1002/ps.481}}</ref> It appears to knock the sea lice off the fish, leaving them capable of reattaching to other fish and reinitiating an infection.

===In-feed treatments===
In-feed treatments are easier to administer and pose less environmental risk than bath treatments. Feed is usually coated with the drug and drug distribution to the parasite is dependent on the [[pharmacokinetics]] of the drug getting in sufficient quantity to the parasite. The drugs have high selective toxicity for the parasite, are quite lipid-soluble so that there is sufficient drug to act for approximately 2 months, and any unmetabolized drug is excreted so slowly that there are little to no environmental concerns.

====Avermectins====
[[Avermectin]]s belong to the family of macrocyclic lactones and are the major drugs used as in-feed treatments to kill sea lice. The first avermectin used was [[ivermectin]] at doses close to the therapeutic level and was not submitted for legal approval for use on fish by its manufacturer. Ivermectin was toxic to some fish, causing sedation and [[central nervous system depression]] due to the drug's ability to cross the [[blood–brain barrier]]. Emamectin benzoate, which is the active agent in the formulation SLICE,<ref>{{cite web |publisher=[[Schering-Plough Animal Health]] |url=http://www.spaquaculture.com/default.aspx?pageid=545 |access-date=September 11, 2009 |title=Slice* Premix |archive-url=https://web.archive.org/web/20090917162111/http://www.spaquaculture.com/default.aspx?pageid=545 |archive-date=2009-09-17 |url-status=dead }}</ref> has been used since 1999 and has a greater safety margin on fish. It is administered at 50&nbsp;μg/kg/day for 7 days and is effective for two months, killing both chalimus and mobile stages. [[Withdrawal time]]s vary with jurisdiction from 68 days in Canada<ref>{{cite web |url=http://www.dfo-mpo.gc.ca/science/enviro/aquaculture/acrdp-pcrda/projects/info-eng.asp?pro=MG-06-04-004&region=MG |title=Depletion of Emamectin Benzoate (SLICE®) from Skeletal Muscle (and Skin) of Atlantic Salmon (''Salmo salar'') following a Multiple Oral (Dietary) 50 μg/kg Dose Regimen, in Seawater at 10 ±1°C; One Laboratory and Two Field-based trials |date=31 March 2007 |work=MG-06-04-004 |publisher=[[Fisheries and Oceans Canada]] |access-date=4 March 2011}}</ref> to 175 degree days in Norway. Avermectins act by opening glutamate-gated chloride channels in arthropod neuromuscular tissues, causing hyperpolarization and flaccid paralysis leading to death. Resistance has been noted in ''Chalimus rogercresseyi'' in Chile and ''L. salmonis'' on North Atlantic fish farms. The resistance is likely due to prolonged use of the drug leading to up-regulation of P-glycoprotein,<ref>{{cite journal |author1=N. D. Tribble |author2=J. F. Burka |author3=F. S. B. Kibenge |author4=G. M. Wright |year=2008 |title=Identification and localization of a putative ATP-binding cassette transporter in sea lice (''Lepeophtheirus salmonis'') and host Atlantic salmon (''Salmo salar'') |journal=[[Parasitology (journal)|Parasitology]] |volume=135 |issue=2 |pages=243–255 |pmid=17961285 |doi=10.1017/S0031182007003861|s2cid=25656517 }}</ref> similar to what has been seen in nematode resistance to macrocyclic lactones.<ref>{{cite journal |author1=Anne Lespine |author2=Michel Alvinerie |author3=Jozef Vercruysse |author4=Roger K. Prichard |author5=Peter Geldhof |year=2008 |title=ABC transporter modulation: a strategy to enhance the activity of macrocyclic lactone anthelmintics |journal=[[Trends in Parasitology]] |volume=24 |issue=7 |pages=293–298 |pmid=18514030 |doi=10.1016/j.pt.2008.03.011}}</ref>

====Growth regulators====
Teflubenzuron, the active agent in the formulation Calicide,<ref>{{cite web |author=EMEA |year=1999 |title=Teflubenzuron, summary report |url=http://www.emea.europa.eu/pdfs/vet/mrls/054799en.pdf |access-date=September 11, 2009 |archive-url=https://web.archive.org/web/20070710212612/http://www.emea.europa.eu/pdfs/vet/mrls/054799en.pdf |archive-date=2007-07-10 |url-status=dead }}</ref> is a [[chitin]] synthesis inhibitor and prevents moulting. It thus prevents further development of larval stages of sea lice, but has no effect on adults. It has been used only sparingly in sea lice control, largely due to concerns that it may affect the moult cycle of non-target [[crustacean]]s, although this has not been shown at the concentrations recommended.<ref name=Burridge/>

===Vaccines===
A number of studies are underway to examine various antigens, particularly from the gastrointestinal tract and reproductive endocrine pathways, as vaccine targets, but no vaccine against sea lice has been reported to date. Two published studies have tested vaccine candidate antigens against salmon lice, which resulted in a reduced infection rate.<ref>{{Cite journal|last1=Grayson|first1=T. H.|last2=John|first2=R. J.|last3=Wadsworth|first3=S.|last4=Greaves|first4=K.|last5=Cox|first5=D.|last6=Roper|first6=J.|last7=Wrathmell|first7=A. B.|last8=Gilpin|first8=M. L.|last9=Harris|first9=J. E.|date=1995-12-01|title=Immunization of Atlantic salmon against the salmon louse: identification of antigens and effects on louse fecundity|journal=Journal of Fish Biology|language=en|volume=47|pages=85–94|doi=10.1111/j.1095-8649.1995.tb06046.x }}</ref><ref>{{Cite journal|last1=Carpio|first1=Yamila|last2=Basabe|first2=Liliana|last3=Acosta|first3=Jannel|last4=Rodríguez|first4=Alina|last5=Mendoza|first5=Adriana|last6=Lisperger|first6=Angélica|last7=Zamorano|first7=Eugenio|last8=González|first8=Margarita|last9=Rivas|first9=Mario|title=Novel gene isolated from ''Caligus rogercresseyi'': A promising target for vaccine development against sea lice|journal=Vaccine|volume=29|issue=15|pages=2810–2820|doi=10.1016/j.vaccine.2011.01.109|pmid=21320542|year=2011}}</ref>

=== Optical methods ===
A more recent advance in the delousing strategy is to use pulsed lasers operating at the wavelength of 550&nbsp;nm to delouse.<ref>{{Cite news|url=https://spectrum.ieee.org/licehunting-underwater-drone-protects-salmon-with-lasers|title=Lice-Hunting Underwater Drone Protects Salmon With Lasers|work=IEEE Spectrum: Technology, Engineering, and Science News|access-date=2017-06-05|language=en}}</ref>

==Other points of interest==
[[Branchiura]]ns, family Argulidae, order Arguloida are known as fish lice and parasitize fish in freshwater.

==See also==
{{portal|Crustaceans}}
* [[Aquaculture of salmon]]
* [[Fish diseases and parasites]]
* [[Salmon louse]]

==References==
{{Reflist|32em}}

==External links==
{{Commons category|Caligidae}}
{{Wikispecies|Caligidae|Caligidae}}
* DFO Canada information on sea-lice [http://www.dfo-mpo.gc.ca/aquaculture/lice-pou-eng.htm]
*Pacific Salmon Forum Interim Results [http://www.dfo-mpo.gc.ca/aquaculture/RD2009/rdsealice-pou_01-eng.htm]
* [http://www.watershed-watch.org/ Watershed Watch Salmon Society] British Columbia advocacy group for wild salmon.
* [http://www.watershed-watch.org/sealice.html Wild Salmon in Trouble: ''The Link Between Farmed Salmon, Sea Lice and Wild Salmon''] - Watershed Watch Salmon Society. Animated short film based on peer-reviewed scientific research.
* [http://www.watershed-watch.org/programs/AquaculturalRevolution.html Aquacultural Revolution: ''The scientific case for changing salmon farming''] - Watershed Watch Salmon Society. Short video documentary by filmmakers Damien Gillis and Stan Proboszcz. Prominent scientists and First Nation representatives speak their minds about the salmon farming industry and the effect of sea lice infestations on wild salmon populations.
* [https://web.archive.org/web/20100103205837/http://www.farmedanddangerous.org/page/sealice ''Sea Lice''] - Coastal Alliance for Aquaculture Reform. Overview of farmed to wild salmon interactive effects of sea lice.
* [https://web.archive.org/web/20090501102114/http://www.farmedanddangerous.org/page/salmon-farming-problems ''Salmon Farming Problems''] - Coastal Alliance for Aquaculture Reform. Overview of environmental impacts of salmon farming.
* [http://www.biologynews.net/archives/2007/12/13/fish_farms_drive_wild_salmon_populations_toward_extinction.html ''Fish farms drive wild salmon populations toward extinction''] Biology News Net. December 13, 2007.
* [https://web.archive.org/web/20100306073336/http://www.st-andrews.ac.uk/~merg/sea%20lice.htm ''Ecological Genetics of Parasitic Sea Lice''] University of St Andrews Marine Ecology Research Group.
*[http://en.wikivet.net/Sea_Lice Sea Lice] expert reviewed and published by [[WikiVet]]

{{plankton}}
{{Fish disease topics}}
{{Fisheries and fishing}}

{{Taxonbar|from=Q3808922}}
{{Authority control}}

[[Category:Siphonostomatoida]]
[[Category:Parasitic crustaceans]]
[[Category:Ectoparasites]]
[[Category:Animal parasites of fish]]
[[Category:Veterinary parasitology]]
[[Category:Taxa named by Hermann Burmeister]]