Clarification on Salmon Mortality - MOWI - Scotland

Clarification on Salmon Mortality

We wish to clarify the position in response to a recent article “Poached alive – fish die as farm overheats water” which appeared in The Telegraph (19th November) and subsequently in the Mail on Line.

The Telegraph article was based on a story in The Sunday Herald the week before based on a Freedom of Information enquiry made by them.

Our fish were most definitely not poached alive or boiled alive as these stories state. This is gross exaggeration and completely misleading.

Attached is a background note on how the Thermolicer operates which explains fish are only ever exposed to an elevated temperature of a maximum of 340C for 25 to 30 seconds.

The Thermolicer has been rigorously tested over a nine year period and is recommended by the Norwegian Veterinary Institute. The machine has safely treated hundreds of thousands of tonnes of salmon in Norway and Scotland.

It is extremely regrettable we lost fish at Greshornish which we believe was the result of treating fish that had been weakened from other treatments, particularly for Amoebic Gill Disease, in the preceding two months. Human error played a part in this incident; however these earlier treatments had saved many fish suffering from this environmental gill challenge. In hindsight it is our belief that any bath treatment for sea lice would likely have resulted in mortality.

The Greshornish experience has understandably raised much internal and external discussion. In particular it highlights the fine line in judgement required on how, and when, we treat our fish stocks. We aim to prevent this happening again by raising awareness with staff and increased training.

Background to the Thermolicer

The Thermolicer is a machine for commercial scale dip or bath treatment to remove sea lice from farmed salmon.

Salmon are gently crowded and pumped into the machine where they pass through the processing loop in 25–30 seconds from where they can then be returned to the same pen or an empty pen. The treatment water has a temperature of 30–340 C, depending on the ambient sea temperature, and because sea lice have a low tolerance to temperature change the higher water temperature will kill the lice. The treatment water is then filtered, aerated, oxygenated and reused in the system.

The Thermolicer can be installed on a boat or a barge and will treat up to 80 tonnes of fish per hour.


  1. Fish enter theThermolicer after pumping.
  2. Water separation.
  3. Sea water is filtered and released.
  4. The fish is exposed to lukewarm water.
  5. Treatment loop.
  6. Water surface.
  7. Water separator for treatment water.
  8. Fish exits the system.
  9. Heated water is circulated to water tank for filtration, aeration and reheating.
  10. Treatment water is pumped back to the treatment loop.

The Thermolicer is recommended by the Norwegian Veterinary Institute as an alternative to the traditional use of medicines for the treatment of sea lice. It is estimated over  one million tonnes of salmon and trout have been successfully treat with the Thermolicer.

Over 30 Thermolicers are currently in use in the salmon farming industry. The manufacturer of the Thermolicer is Steinsvik, a Norwegian company specialising in delivering products and solutions to the aquaculture, maritime industries and the oil and gas industries.

For further reading please see: (Elliot, J. M., 1981. Some aspects of thermal stress on freshwater teleosts. In: Stress and Fish (Ed A. D. Pickering). Academic press, London, 209-245. )

Thermolicer due for delivery to MHS at the end of November.
Thermolicer due for delivery to MHS at the end of November.

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