There are approximately 200 known species of Caligus and 90 species of Lepeophtheirus, most of which are parasitic on marine fish Although large numbers of sea lice are usually associated with commercial fish farming, sea lice originated from wild fish and, as early as 1940, long before the development of intensive fish farming, there were reports of high numbers of lice causing severe damage/mortality in wild fish

More recently, research in Norway and Japan has shown that in some areas sea lice are common on wild salmonids in the open

While Lepeophtheirus salmonis and Caligus elongatus are the most important species affecting farmed fish in the northern hemisphere, other species of parasitic copepods are becoming a problem as fish farming expands world-wide and more species of fish are being cultured.

Life-cycle of Sea Lice

This life-cycle consists of three phases:

  • Free-swimming larval stages - Nauplius I, nauplius II & copepodid.

  • Immature attached stages - Copepodid, chalimus I, II, III and

  • Motile stages - (Lepeophtheirus) Pre-adult I, Pre-adult
    - (Caligus) Mature adults

Disease reprinted courtesy of OIE Diagnostic Manual for Aquatic Animal Diseases, OIE (World Organisation for Animal Health), Paris, France.