Sea lice are small crustaceans that live as external parasites primarily on marine fish. They are a common occurrence in marine environments, affecting various fish species.
Biological Characteristics
Sea lice are classified as copepods, a group of tiny crustaceans. They possess flattened bodies and specialized structures that aid in attachment. These ectoparasites feed on the mucus, epidermal tissue, and blood of their host fish. While numerous species exist, Lepeophtheirus salmonis is particularly well-known for affecting salmon.
Life Cycle and Hosts
The life cycle of sea lice involves both free-swimming and parasitic stages. Eggs hatch and develop into an infective stage that actively seeks a suitable fish host. Once a host is found, they attach and mature through several stages, eventually becoming mobile on the fish’s surface and able to move between hosts. Sea lice primarily parasitize marine fish, including wild and farmed species like Atlantic salmon. Their development rate is significantly influenced by water temperature, with warmer temperatures accelerating their life cycle.
Impact on Marine Life and Aquaculture
Sea lice infestations can have negative effects on fish health. Their attachment and feeding activities cause physical damage to the fish, leading to skin lesions and open wounds. This physical trauma can stress the fish, disrupt their ability to regulate internal salt and water balance, and make them more susceptible to secondary infections. Severe infestations can result in reduced growth rates, poor overall welfare, and increased mortality.
The aquaculture industry, particularly salmon farming, faces substantial economic challenges due to sea lice. Farmers incur costs from fish losses, reduced fish growth, and expenses for treatment and prevention. In 2011, sea lice parasitism was estimated to cause $436 million in damages to the Norwegian salmon industry alone. Sea lice from aquaculture facilities can also spread to wild fish populations, especially juvenile salmon, potentially impacting their survival.
Human Interaction and Misconceptions
A common misunderstanding is that the skin irritation experienced by swimmers, often called “sea lice rash,” is caused by the same parasites that affect fish. True sea lice, which are fish parasites, do not typically bite or affect humans. They are highly host-specific and cannot survive on human skin.
The rash commonly referred to as “sea lice” or “seabather’s eruption” is instead caused by the larvae of jellyfish or other marine organisms. These tiny larvae can become trapped under swimwear, and when compressed or irritated, they release stinging cells that cause an itchy, red rash. Symptoms may appear while still in the water or several hours later, lasting from a few days to a couple of weeks, but they are not contagious.
Management and Prevention in Aquaculture
Managing sea lice in aquaculture involves various strategies. One biological approach utilizes “cleaner fish,” such as wrasse and lumpfish, which naturally feed on sea lice attached to salmon. This method offers an alternative to chemical treatments.
Other strategies include freshwater treatments, which sea lice cannot tolerate, and mechanical removal techniques. Specific medications can also be used, though resistance development necessitates careful management. Farm site selection, using oceanographic modeling to avoid high-risk areas, and coordinated fallow periods among farms also contribute to prevention by reducing parasite loads.