infection. Pacific L. salmonis can also develop, but not complete, its full lifecycle on the three-spined stickleback (Gasterosteus aculeatus). This has not been observed with Atlantic L. salmonis.

How planktonic stages of sea lice disperse and find new hosts is still not completely known. Temperature, light, and currents are major factors and survival depends on salinity above 25 ?. L. salmonis copepodids migrating