Salmon louse

Caligus elongatus is a species of copepod crustacean belonging to the family Caligidae within the order Siphonostomatoida. It is widely recognized as a serious ectoparasite in marine environments, impacting a diverse range of wild and farmed fish species across the Northern Hemisphere.

This parasite is known for its low host specificity, meaning it can infest various commercial species, including Atlantic salmon, cod, and herring. Unlike some more host-restricted lice, it thrives in varied salinity and temperature conditions, making it a persistent challenge for marine aquaculture facilities.

The life cycle consists of free-living naupliar and copepodid stages, followed by attachment and maturation on the host fish. The copepodid stage is the infectious phase, where the parasite actively seeks a host. Once attached, it molts through several chalimus stages before becoming a mobile adult capable of moving across the host's body.

The damage caused by Caligus elongatus is primarily mechanical and physiological. By grazing on the fish’s mucus, skin, and underlying tissues, the parasite creates open wounds. These lesions are not only painful but also compromise the fish's osmoregulation and leave them vulnerable to secondary bacterial and viral infections.

Effective management strategies require a multi-faceted approach. Industry practices include:

• Regular counting and monitoring of lice burdens on fish stocks.
• Use of chemotherapeutants or targeted veterinary medications.
• Mechanical removal techniques such as thermal or hydro-licing systems.
• Biological control using cleaner fish species to reduce lice populations in cages.
• Environmental management and optimized site selection for fish farms.