ABSTRACT
Although most people think of copepods as primarily free-living animals this is not the case as over half of all the known species of copepods live in association with other organisms (Huys and Boxshall, 1991). Of these species the nature of their associations ranges from being symbiotic to truly parasitic during some or all of their life history stages. For the purpose of this chapter we are defining sea lice as those species that are in the genera Lepeophtheirus (Nordmann, 1832) and Caligus (Müller, 1785). These genera belong to the order Siphonostomatoida and family Caligidae. Species within these genera are ectoparasites of a wide variety of species of fish in marine and brackish waters.
