Sea Lice   Lepeophtheirus salmonis

The term sea lice refers to several parasitic copepods with the scientific names of Lepeophtheirus and Caligus.  They are found throughout the world's oceans parasitizing the skin of a variety of fish including various species of salmon by feeding on the skin and blood.  A type of crustacean, most copepods are common members of the zooplankton community where they are free swimming and eat phytoplankton

The photograph shows four female sea lice (Lepeophtheirus) attached near the anal fin of a salmon.  The body of the sea lice is composed of the large round head and thorax which attaches to the skin of the fish using small legs and other anchoring mechanisms, the paired reproductive organ and the twin egg sacs.  A male is smaller and lacks the swollen reproductive organs.

Lepeophtheirus is the common copepod parasite on local salmon which in low numbers causes minimal damage.  However large numbers can lead to severe effects including death.  The life history is complex with several free swimming forms and several attached pre-adult forms which cause the most damage to the host. For more information go to

Farmed salmon are highly susceptible to infestation by sea lice.  Various husbandry practices as well as  chemicals can be used to control sea lice populations in pens.  Controversy over the potential for salmon farms to spread the lice to wild populations is discussed in a study published the fall of 2008 in the journal "Science".