Sea lice

Published 02 Oct 2017

Sea lice are crustacean parasites of the copepod family Caligidae, which cause infection in wild and farm fish especially salmon. It is a great cause of concern for the fish farmers because sea lice infection can literally threaten to wipe out the whole fish population if this parasite gets a chance to thrive well. Almost nine, or according to some sources, more than nine species of sea lice are present out of which two very common are Caligus elongatus and Lepeophtherius salmonis. Around fifty different species of marine fish are believed to host the Caligus elongatus specie of sea lice alone. Salmons and related species like rainbow trout etc. are infected by Lepeophthelius salmonis. Seal lice are most common in sea water and it is believed that they cannot survive very low salinities, however very low salinities may not be suitable for some fish either.

During the early stages of the life cycle of sea lice, when they are in the stage of naupii, they are non-parasitic and cannot attach themselves to the fish. However, during the final stages, when sea lice have attained mobility they are capable of causing excessive damage to the body of the fish as parasites. A range of signs of the infection are prominent on the bodies of the fish including black spots, lesions, lowered immunity and increased susceptibility to other infections. It is believed that L. salmonis causes more damaging infection than C. elongatus.

Sea lice control in fish farms (especially salmon aquaculture) should be conducted after consulting with the farm veterinarian. Specific scientific monitoring programs should be developed. The programs should fully take into account the frequency of monitoring required, the number of fish and cages to be monitored each time, ensuring minimal stress to the fish while monitoring and assessing damage using lesion index and the number of infected fish as basis. Analysis of the monitoring team will provide the basis of treatment if required at all. If any specie of sea lice is found by the monitoring team, (however only the two above mentioned species are most commonly detected), then treatment is essential to prevent the lice from causing huge damage to the produce of the farm. Trained staff and appropriate equipment are needed for an effective control program. Chemotherpeutants used for treating the fish infection, range from topical baths, including organophosphates and pyrethroids, and feed treatments which include avermectins and benzoylphenylurea.


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