There has been some research on the problems caused by this species in aquaculture, but little is known about the salmon louse's life in nature. It has been shown, however, that salmon louse infections in fish farming facilities can cause epizootics in wild fish.
The life cycle consists of 8 stages, with ecdysis in between. The first two stages are free swimming nauplius I and II, where it has a length between 0.54 and 0.85 mm. The third stage is the copepodit stage, in which the length is ca. 0.7 mm, and the salmon louse attaches itself to the fish. Stages IV and V are the chalimus stages. The salmon louse eats from the fish, and grows to a length of 5 mm for the males, 10 mm for the females. Each generation takes about six weeks at a temperature of 10–12 °C (50–54 °F). In the pre-adult and adult stages (stage VI to IIX), the sea louse is now mobile, and it becomes possible to differentiate males and females.
The thorax is broad and shield shaped. The abdomen is narrower, and in the females, filled with eggs. The females also have two long egg strings attached to the abdomen. The salmon louse uses its feet to move around on the host or to swim from one host to another.