Factsheet On Sea Lice

FACTSHEET October 2009

A factsheet on sea lice. Dispersion, regulations, measures and results.

Sea lice

A minor parasite causes major challenges

Why we have to fight sea lice Sea lice are naturally occuring in marine waters, and can move through the waters and therefore transfer from wild fish to farmed fish and vice versa. Lice can attach to the skin of the fish where they live and breed. This can cause wounds that may lead to problems with the salt balance and result in infections. An attack of ten lice on a small fish could be fatal.

The sea louse is an external parasite with salmonids as its host, i.e. salmon, trout, rainbow trout and Arctic char. Photo: T. Poppe/NVH

Sea lice represent a challenge for the aquaculture industry and for wild salmonids. Salmon fish farmers use significant resources to keep the level of sea lice low in the fish farming facilities. The main aim for the fish farming industry is that sea lice from fish farming facilities will not have a negative effect on the wild fish populations. Sea lice are naturally occurring parasites of wild salmonids, and in our waters two species are

described: Lepeophtheirus salmonis preying on salmon and Caligus elongatus that prey on more than 80 different species including salmon and cod. Lepeophtheirus salmonis represents the biggest challenge. Sea lice are a crustaceans that grow by changing its shell between the different stages of development. During the three free living stages lice can spread over large areas through the waters. When it attaches itself to a salmon, it develops further through four fixed stages and three mobile stages, and ends up

Wrasse (cleaning fish) eat up the problem

The development of salmon farming along the coast has made it easier than previously for the sea lice to find hosts (salmon) in the sea. Lice levels in the fish farming facilities are therefore kept very low and do not constitute a health problem for the fish in salmon aquaculture, but the levels of lice in the fjords may result in increased pressure of infection for wild salmonids. Norway has important wild salmon stocks and a significant aquaculture industry. It is important to preserve both. Lice infection can affect the welfare and growth of farmed salmon and thus also value creation in aquaculture. It is therefore also in the fish farmers’ interest to keep the sea lice level in the facilities as low as possible.

Wrasse.

Species of wrasse such as goldsinny, corkwing and ballan eat lice that have Photo: Villa Organic attached to salmon. Wrasse can therefore be used for natural de-lousing, and have showed a good effect along the cost north up to and including Lofoten. Given the requirement for a very low level of lice in the aquaculture facilities, the wrasse represents a supplement to other methods of fighting the problem. The farming of ballan wrasse is underway to improve access to wrasse.

Regulations to fight sea lice All efforts to manage the sea lice are based on regular monitoring procedures. If the lice infection at a facility exceeds a certain level, a treatment scheme is initiated. Medicines are prescribed by fish health personnel and are approved for use in aquaculture. In 2009 revised sea lice regulations are being drawn up with measures to reduce the risk of developing resistance. This is being carried out in collaboration with FHL/the aquaculture industry, authorities and other expert bodies.

New and old weapons Several tools are used to fight sea lice. The effect is tested after treatment. In this way the fish farmer can identify any reduced effect or resistance developed, and follow up with the use of other tools. The coordination of delousing measures ensures that all facilities within a geographical area reduce the pressure of lice in the sea.

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Bath treatment: Approved medicine against sea lice is added to the water in the fish farming net cages, that are shielded fully or partially using a so-called “skirt” or tarpaulin. Special feed: Approved medicine is added to feed for a period. The medicine stops the developing lifecycle of the lice.

Delousing. Fish farming nets are shielded using tarpaulins before treatment start. Photo: National Veterinary Institute

as an adult louse that breed on the fish. She releases the fertilised eggs into two sacks, “egg strings”. A female can produce up to 10-11 pairs of such sacks, each containing several hundred eggs, during her lifetime. Sea lice are marine parasites and generally fall off the salmon after a short time in fresh water. Wild salmon bring lice with them from the sea when they travel into the coastal areas during the spring to spawn in the rivers. Sea trout live in the fjords and coastal waters all year round and like farmed fish they can help to maintain the continuous production of sea lice. Thus in practice it is possible for lice to travel between wild fish and farmed fish and vice versa.

Wrasse: Cleaning fish that live in the net cages and eat lice attached to the farmed fish.

In salmon fish farming lice levels are continuously monitored according to legal requirements, by having the number of lice counted every 14 days.

Vaccine developments: There are few vaccines against ectoparasites but the industry believes that it is possible to develop a vaccine against sea lice.

The countings of lice are reported to the Norwegian Food Safety Authority and the results are available at www.lusedata.no.

Breeding against lice: Can be pertinent in the longterm.

Whenever regulatory treatment trigger levels are exceeded, measures are put in place to reduce the lice levels. Effective treatment measures

Other sources Lakselus.no: www.lakselus.no The Norwegian Food Safety Authority: www.mattilsynet.no The Fishery and Aquaculture Industry Research Fund: www.fhf.no

have existed for several years having led to sea lice not generally representing a health problem for farmed salmon. During 2008 certain areas along the coast reported that sea lice showed reduced sensitivity to some of the anti-parasite preparations. This represents a serious challenge for fish farmers, and potentially for wild fish. New measures have been put in place, including coordinated, synchronous delousing campaigns, and the lice situation in the spring of 2009 showed that the measures implemented during the winter had given the desired effects. This reduced the pressure of infection on wild salmonids in the fjord systems. In order to succeed in the fight against sea lice it is vital that all known measures are implemented, used correctly and by all fish farmers. Medicines are only used when necessary. Other important efforts in the fight against sea lice, are preventive measures, use of wrasse as well as further research and development on new measures. Developing of a new vaccine and breeding methods to produce salmon that are more robust against the parasite, is also on the agenda.

This factsheet is published by The Norwegian Seafood Federation (FHL). Comprehensive information about sea lice and other relevant topics can be found in FHL’s Environmental Report for 2008. FHL is the largest employer organisation for the seafood industry and covers the entire value chain, from fjord to table. FHL is affiliated with NHO. See also www.fhl.no/miljo