The Salmon Louse Lepeophtheirus salmonis (Copepoda: Caligidae) life cycle has only two Chalimus stages

PLoS One. 2013 Sep 12;8(9):e73539. doi: 10.1371/journal.pone.0073539. eCollection 2013.


Each year the salmon louse (Lepeophtheirussalmonis Krøyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L. salmonis. Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Copepoda / growth & development*
  • Larva / growth & development
  • Life Cycle Stages / physiology

Grant support

This research has been funded by the Research Council of Norway (RCN) and the Norwegian Seafood Research Fund (FHF) through the SFI-Sea Lice Research Centre (RCN grant number 203513) and the PrevenT project (FHF grant number 900416 and RCN grant number 199778). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.