also known as: salmon louse, sea lice, Lepeophtheirus, Salmincola, fish lice
Copepods are crustacean ectoparasites of salmonids and other fish species and commonly found throughout Oregon. Many reservoirs go through episodes of high freshwater copepod prevalence in fish. The two primary species encountered in the Pacific Northwest are Lepeophtheirus salmonis and Salmincola sp. They can be found commonly on salmonids that are returning to fresh water to spawn. Fishermen often refer to them as "fish lice". Parasitic copepods feed on skin, mucus and blood from salmonid hosts. Usually there are few parasites present on fish and they go unnoticed, however occasionally they can become numerous and quite evident on gills, in the mouth and at the base of the fish’s fins. When present in extremely high numbers they can cause a fish health problem but this is rarely seen in the wild. Marine copepods will survive for some time in fresh water but eventually die and drop off. Sealice can cause problems in fish raised in saltwater net pens. The parasite poses no risk to humans or domestic animals.