Information on Sea Lice

Sea lice (singular sea louse) are a group of parasites that harbor in warm sea waters. They are planktonic and often transported through tides. In general, they reside in marine fish, especially salmon and sea trout. In recent times, the population of sea trout has decreased tremendously due to heavy infestation of sea lice. Though many species of sea lice are identified, two species namely, Caligus elongates and Lepeophtheirus salmonis, are known to cause heavy infestations in salmon. Sea lice infestation in adult fish is relatively less dangerous as compared to infestation in juvenile fish.

Sea Lice Life Cycle

The life cycle of sea lice encompasses ten stages, excluding the egg stage. The first three stages of sea lice are motile and non-parasitic. The female sea lice carries the eggs in long trails and lays in favorable conditions. The egg hatches into Nauplius 1 that gives rise to Nauplius 11 after molting. Both Nauplius possess distinctive appendages and are actively motile. The third motile stage of sea lice is the Copepodid stage. The Copepodid undergoes molting, which develops to the first parasitic larval stage with a frontal filament, the Chamilus.

The Chamilus moults through four successive stages. It is found commonly in the fins and tails of marine fish. The Chamilus larvae then develops into preadults 1 and II that are found within the scales of fish. Finally, the preadult II moults and develops into the adult sea lice that are visible with naked eye. The adult female is larger than male sea lice and possesses long trails. The preadult and adult stages of sea lice cause maximum fish mortality. The lifespan of sea lice may range from 6-8 weeks depending upon the species.

Sea Lice Quick Facts

• Sea lice thrive well in warm temperature ocean waters and are not tolerant to cold conditions.
• They die immediately after an exposure to fresh water.
• Sea lice feed on the mucous lining, skin and blood of marine fish.
• They affect certain populations of wild and farm fish.
• The studies have revealed that sea lice 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 the population of sea lice under control.
• The mortality rate of fish due to sea lice infestation is highest in salmon.

If the outbreaks of sea lice 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. This chemical is usually mixed with the fish food and feed to the farmed salmon. However, the safety of the chemical and its impact on human health is controversial. Considering this, many state governments have banned salmon farming.

Sea Lice Bites

Sea lice are also a major threat to the divers and swimmers at the sea beach. The larvae of sea lice stings and causes burning sensation, itching, reddening, 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 may 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 sea lice bites is application of vinegar on the affected skin area. As heavy outbreaks of sea lice are observed from April to August, an extra care should be taken while swimming or diving during these months.