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. See also Aquaculture of salmon Fish diseases and parasites Salmon louse References External links DFO Canada information on sea-lice Pacific Salmon Forum Interim Results Watershed Watch Salmon Society British Columbia advocacy group for wild salmon. 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