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). 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. fish farming control on salmon farms this has been reviewed by pike & wadsworth, mcvicar, and costello. integrated pest management programs for sea lice are instituted or recommended in a number of countries, including canada, norway, scotland, and ireland. identification of epidemiological factors as potential risk factors for sea lice abundance with effective sea lice monitoring programs have been shown to effectively reduce sea lice levels on salmon farms. 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. 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. research then began to identify trait markers, 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. 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. in 2017, salmon prices in norway increased by 15% over a 3-month period because of a sea lice outbreak. treatments freshwater freshwater is sometimes adequate to kill the sea lice and as salmon eventually swim in fresh water, they are not harmed. 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. 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. 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. 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. 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 mg/l for 20 min) will remove mobile sea lice from fish. it is environmentally friendly since h2o2 dissociates to water and oxygen, but can be toxic to fish, depending on water temperature, as well as to operators. 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 avermectins 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, has been used since 1999 and has a greater safety margin on fish. it is administered at 50 µg/kg/day for 7 days and is effective for two months, killing both chalimus and mobile stages. withdrawal times vary with jurisdiction from 68 days in canada 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, similar to what has been seen in nematode resistance to macrocyclic lactones. growth regulators teflubenzuron, the active agent in the formulation calicide, 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 crustaceans, although this has not been shown at the concentrations recommended. 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. optical methods a more recent advance in the delousing strategy is to use pulsed lasers operating at the wavelength of 550 nm to delouse. other points of interest branchiurans, family argulidae, order arguloida are known as fish lice and parasitize fish in freshwater.