Sea Lice Life Cycles

The sea lice life cycle consists of 10 different stages (plus the egg stage), with a moult between each one. The entire life cycle for Lepeophtheirus salmonis is about 7-8 weeks at 10^oC, and for Calimus elongatus, it is about 6 weeks.

The life cycle for L. salmonis includes nauplii, copepodid,
calimus, preadult and adult stages.

The life cycle for C. Elongatus includes nauplii, copepodid,
calimus, and adult stages.

The first stages in the life of a sea louse after it has hatched out of its egg is the Nauplius I & II stages.  At this point, it is free swimming, and has very noticeable appendages.

The next stage is the Copepodid stage.  This is another free swimming stage, but the organism takes on a more rice like shape, with less noticeable appendages.

After the Copepodid stage comes the first parasitic stages - the Chalimus I-IV stages.  At this stage, the louse develops a structure called a frontal filament which allows the louse to attach to the fish.  Chalimus are often seen hanging off the edge of gills and fins.

Chalimus larvae then moult into preadults (in L. salmonis).  The preadult stage is usually not attached to the fish by a frontal filament, however it often buries under scales to keep very close to the host.

Once they reach the adult stage, the sea lice are easily seen with the naked eye. The male is smaller, and the female has wider "hips".  Females that have eggs keep them in long strands that trail behind them.