Information on Sea Lice

Sea lice are small parasites, which are commonly found in salmon and other marine fish. In humans, they are known to cause skin irritation and lesions.
Sea lice are planktonic parasites that harbor in warm sea water, and are often transported through tides. In general, they reside in marine fish, especially salmon and sea trout. In recent times, the sea trout population has decreased tremendously due to heavy sea lice infestation. Though many species of sea lice are identified, two species namely, Caligus elongates and Lepeophtheirus salmonis, are known to cause heavy infestations in salmon. Their infestation in adult fish is relatively less dangerous as compared to infestation in juveniles.

Life Cycle

The life cycle of sea lice encompasses ten stages, excluding the egg stage. The first three stages are motile and non-parasitic. The female sea louse carries the eggs in long trails and lays them in favorable conditions. The egg hatches into Nauplius I that gives rise to Nauplius II after molting. Both Nauplius possess distinctive appendages and are actively motile. The third motile stage is the Copepodid stage. The Copepodid undergoes molting, which develops to the first parasitic larval stage with a frontal filament, the Chamilus.

The Chamilus molts through four successive stages. It is found commonly in the fins and tails of marine fish. The Chamilus larvae then develops into preadults I and II that are found within the scales of fish. Finally, the preadult II molts and develops into the adult sea lice that is visible to the naked eye. The adult female is larger than the male and possesses long trails. The preadult and adult stages of sea lice cause maximum fish mortality. Their lifespan may range from 6 - 8 weeks depending upon the species.

Quick Facts
  • Sea lice die immediately after exposure to freshwater.
  • Sea lice feed on the mucous lining, skin, and blood of marine fish.
  • They affect certain populations of wild and farm fish.
  • Studies have revealed that they are transmitted from wild fish to farm fish when the former return to natural streams for spawning.
  • Monitoring of sea lice is done before salmon fish farming, in order to keep their population under control.
  • The mortality rate of fish due to sea lice infestation is highest in salmon.
If the outbreaks continue in salmon, there is a possibility of salmon extinction. At present, majority of salmon fish farmers use a chemical (emamectin benzoate) to kill sea lice. It is usually mixed with fish food and fed to farmed salmons. However, the practice has been shrouded by controversies about the safety of the chemical and its impact on human health, and thus, many state governments have banned salmon farming.

Sea Lice Bites

These parasites threaten divers and swimmers at the beach as well. The sting of its larvae can cause burning sensation, itching, reddening, and elevated skin, which later progresses to skin rash and skin lesions. These lesions may remain for about 1 - 2 weeks. In severe reactions, the symptoms of sea lice bites include fever, headache, nausea, and vomiting. Topical corticosteroids and dilute hydrogen peroxide can be applied to the affected area for quick healing and to impede other skin infections. An effective home remedy for their bites is application of vinegar on the affected skin area.

As heavy outbreaks of sea lice are mainly observed from April to August, extra care should be taken while swimming or diving during these months.