Sea Lice: Wild Infection Equally Significant

The Fish Site
by The Fish Site
10 December 2007, at 12:00am

NORWAY - A recently completed PhD thesis 'Host selection and infection strategies in Caligus elongatus' has proved that the sea louse, a parasitic copepod, is widely distributed among wild fish species along the Norwegian coast.

In depth investigations by Dr Scent Øivind Øines found that the parasite, wdecimate desimate productivity in farmed fish stock, is equally troublesome in the wild. The louse is found in large numbers in lumpfish, which is now considered to be a primary host. The lumpfish also acefficientfficienct vector, capable of infecting several types of farmed fish when it arrives in coastal waters during the spring months.

Lumpfish infected with more than 600 sea lice. (Photo: Øivind Øines)

Øivind Øines studied sea lice infestations in wild fish for his PhD degree at the norwegian School Of Veterinary Science, Oslo. Using genetic tools, he discovered more information about the pathways of infection and sources of infestation of this significant fish parasite. His findings increase the understanding of this econdebilitatinglitiating species,and mayvitale a vialt link in combating the parasite in fish farms along Norway's coast.


The sea louse Caligus elongatus is a parasite that attaches to the skin of fish. It can cause sores on its host, which at worst may prove fatal to the fish. It has been found to effect more than eighty different fish species in most or the world’s oceans and has been reported in large numbers on farmed salmonids at sea, but also in other farmed species such as cod and halibut.

“Since sea lice are found on so many different north-Atlantic fish species, it is highly likely that they can transmit from wild fish to farmed fish. Our genetic studies of the parasite also support this. It is also likely that they can transmit between different farmed species”, said Øivind Øines.

During his work, he developed genetic tools for the identification of these parasites and other related parasitic copepods, which may be nearly identical in appearance during several stages of their life cycles. Øines found two different genetic variants of the sea louse on wild fish, each of which appears to have different patterns of infestation.

Øines shows in his thesis that the sea louse (pictured left) is relatively common among wild fish. Fifteen per cent of wild fish were infected with this parasite outside Arendal between 2002 and 2004 - the area covered by the field studies. Øines’ studies have revealed that, in all likelihood, both wild fish and farmed fish become infected. He also identified some of the most important probable sources of infection in the ocean.

The investigations and scientific analysis was carried out in regii of the Norwegian Veterinary Institute in close collaboration with researchers at the Institute of Marine Research at Flødevigen and the University of Oslo.

Further Reading

- For more information on Sea Lice click here.