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Sea lice
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New results change the lifecycle of the salmon louse

New results have shown that the salmon louse has seven larval stages before it develops into an adult. Previously, nine larval stages have been described. As the louse undergoes ecdysis between each stage, the number of molts has also been reduced.

One of the reasons why these studies were initiated was that the salmon louse appeared to have an unusually large number of larval stages compared to related animals. Originally, salmon louse was described to have nine larval stages, but this new study shows that in fact, it only has seven.

-The two stages that have “disappeared” are chalimus stages, where the louse is attached to the host fish by a filament. These stages are difficult to follow since they are small and sitting on the fish. This is one of the reasons why the number of stages was determined wrongly. Also, this new study has revealed that chalimus larvae grow in size between the molt events. Normally, animal with an exoskeleton need to molt to expand in size, the researchers involved in the study says. According to them, it has now been established that the salmon louse chalimus larvae also expand in size between molts.

Important results

The new results are important both for researchers and for the aquaculture industry.
- As a researcher it is obviously important to have as much knowledge as possible about the animal that we study, says the researchers. For the industry information understanding the lifecycle and the number of molts, is interesting because some of the compounds that can be used against salmon lice infestation are inhibitors of the molting process.


The results are published in the scientific journal PlosONE. The article "The Salmon Louse Lepeophtheirus salmonis (Copepoda: Caligidae) Life Cycle Has Only Two Chalimus Stages" has been written by researchers from Institute of Marine Research, University of Bergen (Sea Lice Research Centre), Bergen, Norway, University of Sterling and Natural History Museum in London, both in the UK.

Facts about sea lice

Latin name: Lepeophtheirus salmonis
Distribution: occur naturally in Norwegian waters. Their numbers have risen significantly in parallel with the growth of the aquaculture industry.
Biology: sea lice are parasites with eight life stages, three of which are free-swimming, two of which are stationary and three of which are mobile. They attach themselves to salmon in the third life stage.
Size: adult female: 12 mm (approx. 29 mm including egg strings); adult male: 6 mm.
Diet: the skin and blood of salmonids. The lice only start feeding when they have attached themselves to a host fish (stationary and mobile stages).
Reproduction: all year round, but reproduce increasingly quickly as temperatures rise in spring.
Dispersal: free-swimming stages spread on currents in fjords and coastal waters.
Treatment: biological methods (wrasse) or chemicals (medication).

Sea lice