Sea lice: a never-ending battle

Arvid Hallén Arvid Hallén opened the HAVBRUK 2012 Conference. (Photo: Anne Ditlefsen) At the HAVBRUK 2012 Conference in Stavanger, Norway from 16 to 18 April, the sea lice problem was one of the issues used to illustrate the potential clash between the desire for continued growth vs. environmental considerations in aquaculture.

“We are entirely dependent on further knowledge development if we are to be successful in managing our resources and ensuring sustainable industrial development,” says Arvid Hallén, Director General of the Research Council of Norway.

“The extensive research effort concerning sea lice is a part of this. We cannot just lean back and rely on others; we have to take responsibility ourselves for developing the expertise needed to move the industry forward.”

“In many other areas we can look abroad to find solutions to our problems, but in this case we are at the forefront of the field and must be a leader in producing know-how,” the director general points out.

Part of the natural fauna

Ole Torrissen “The battle against sea lice will require continual advances from research,” believes Dr Ole Torrissen. (Photo: Kjartan Mæstad) Professor Ole Torrissen of the Institute of Marine Research is heading the large-scale research project, Salmon louse - prevention and treatment (PrevenT), which plays an important role in the battle against sea lice. Yet Dr Torrissen does not believe it is possible to come up with an end-all solution to sea lice infestation.

“Sea lice are a natural part of the fauna that we will always have to cope with. It is a tug-of-war requiring an ongoing effort to maintain and improve our position. We will have a continual need for new and effective treatment regimes that employ an arsenal of strategies and medicines,” Dr Torrissen states.

“In addition, we need production systems that can limit infestation. This encompasses breeding programmes, feed products, suitability of locations and the use of cleaner-fish Ballan wrasse,” he says, pointing to interdisciplinary research activities on topics such as genetics, biology, spread rates, resistance and vaccine development currently directed towards combating sea lice.

Testing delousing agents

The results are already emerging. At the HAVBRUK Conference in Stavanger, several contributors presented results from the PrevenT project. 

Among the results presented was a new, simple test for determining which delousing agent would be most effective for a given production facility. Since different groups of lice react differently to various agents, it is essential to know which one is most effective against the lice in that particular area. The test can be administered at the edge of the sea cage and results are available within 24 hours.

Kari Olli Helgesen Fellowship-holder Kari Olli Helgesen picks lice off of a farmed salmon. (Photo: Tor Einar Horsberg ) In simple terms, the test works as follows:

Approximately 30 lice are inserted into jars holding a mixture of filtered seawater and the recommended dosage of the medicines being tested.
After 24 hours, the content of the jars is filtered through a sieve where the leftover lice are tallied. The number of lice in the sieve in relation to the number still attached to the inside surface of the jar indicates the efficacy of the given agent.

“If the delousing agent is effective, the lice will not be able to adhere to the glass, says Professor Tor Einar Horsberg from the Norwegian School of Veterinary Science. Dr Horsberg has been involved in the PrevenT project and headed product development of the test.

“If 75 per cent or more of the lice let go then it is a strong indication that the agent is effective. If half or more remain attached to the glass the effect is considered unacceptable,” says Dr Horsberg.

On the market this year

The simplified diagnostics have been carefully tested. The test concentrations of the various delousing agents are determined through repeated tests on different groups of lice with known sensitivity thresholds.

Illustration Moment of truth: The delousing agent will prove effective if 75 per cent or more of the lice end up in the sieve. (Photo: Tor Einar Horsberg ) “The laboratory results are then compared against small-scale delousing treatments so that we can be confident that the test works,” says Dr Horsberg who hopes that the test can be made available to salmon producers before the end of the year.

“It will happen as soon as we’ve published our results. Using this test, salmon farmers will be able to find out which delousing agent works best, for a reasonable price. This means they will be able to avoid spending vast amounts on delousing treatments that don’t work. Aquaculture health services will be able to apply the test from the edge of the sea cage,” Dr Horsberg claims.

New insights into sea lice from salmon farm data

Several factors determine whether sea lice numbers will swell. These include seawater temperature, salmon size and an area's density of production salmon. Based on the unique salmon production records and sea-lice data accumulated by the aquaculture industry over many years, researchers are developing models that both monitor the population of sea lice and help to predict problems.

"We have just about completed our analysis of the key factors underlying sea lice population growth,” explains Peder A. Jansen from the Norwegian Veterinary Institute. Dr Jansen headed a sub-project on dispersion models as part of the PrevenT project.

“The size of the caged fish is more important than previously believed - large fish have room for more sea lice and have often been exposed to sea lice longer than smaller fish. At the same time, the total population of production salmon in an area is a significant factor behind the proliferation of infectious sea lice larvae, which in turn has an effect on the need for treatment," says Dr Jansen.

Improved management

Under certain conditions, the population of sea lice within an area can grow large enough in scale to make it difficult to keep their numbers down to an acceptable level. Within two years, Dr Jansen hopes to present a model capable of calculating the amount of sea lice within specific areas both in real time and as a forecast for the future. The model will serve as a tool for a variety of players.

"When aquaculture administrators are able to calculate the production of sea lice in specific places they will be in a better position to assess the potential impact on wild fish in the surrounding area or whether the production of fish in certain areas is exceeding its ability to withstand the pressure of infection by lice," Dr Jansen points out.

Optimal locations

If the dispersion model includes data on local currents, the salmon producers will be able to use it to determine which locations will yield the fewest problems with sea lice.

"Backed with funding from the regional research fund for Central Norway, the Norwegian Veterinary Institute in Trondheim and Marine Harvest are developing production facility-specific models for sea lice," states Dr Jansen.

Illustration of the life-cycle of sea lice. Illustration of the life-cycle of sea lice. (Illustration: T. A. Schram)

Facts about sea lice
Sea lice (Lepeophtheirus salmonis) are parasites indigenous to Norwegian waters. Their lifecycle consists of ten separate stages: three free-swimming, four parasitic and three mobile phases. The sea louse attaches itself to the salmon during the third stage and begins feeding on the skin and blood of the fish.
During the first three stages, sea lice are spread by currents in fjords and coastal waters. Reproduction rates increase as water temperatures rise throughout the spring. Current methods of combatting sea lice include biological (e.g. the use of the cleaner-fish Ballan wrasse) or chemical measures.
Source: Institute of Marine Research
 

 

Facts about the knowledge platform PrevenT
  • Project title: Salmon louse - prevention and treatment
  • Interdisciplinary activity to combat sea lice through research on genetics, biology, spread rates, resistance and vaccine development
  • Project period: 2010-2014
  • Project manager: Ole Torrissen, Institute of Marine Research
  • Collaboration between Institute of Marine Research , the Norwegian Veterinary Institute, the Norwegian School of Veterinary Science, the University of Bergen, the Norwegian Institute for Nature Research (NINA), the Norwegian Computing Center and the Centre for Integrative Genetics/Norwegian University of Life Sciences
  • Total budget NOK 18 million (over four years)
  • Receives funding under the Research Council's HAVBRUK programme and the Fishery and Aquaculture Industry Research Fund

 



 

 

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