Philip Lymbery, Compassion CEO

Philip Lymbery

Scottish intensive salmon farming plumbs new depths RSS Feed

Fish farm

Fish farm

Reports that Scottish salmon farms have killed tens of thousands of fish accidentally by overheating them have sent shockwaves through an industry already under fire for shooting seals.

Seals are all too often shot as part of ‘predator control’ around intensive fish farms that are effectively factory farms in the sea.

Now nearly a hundred thousand salmon are reported to have been killed after the use of a new device, the ‘thermolicer’. The device was used in the latest desperate bid to rid intensively farmed fish from lice, a parasite infestation which is inevitable when so many fish are crammed in a confined space.

Information from the Scottish Government, received following a Freedom of Information request by the Global Alliance Against Industrial Aquaculture (GAAIA), reveals that 95,000 fish died on a single Scottish fish farm following the use of a thermolicer.

The thermolicer procedure involves crowding the fish used to the cold coastal waters of Scotland, pumping them into heated water and then dumping them back into their seawater cages. Salmon would never normally experience such sudden temperature changes. Little wonder that so many seem to have died as a result.

Killing fish by overheating, whether accidental or not, is simply inhumane.

The use of rough handling and heat treatment to tackle problems of sea lice is unacceptable on welfare grounds. 

Parasitic sea lice, which look like tiny tadpoles, are one of the single biggest problems for intensive salmon farms. When they latch on to fish, they eat away at the skin and scales. The effect around the head can be so corrosive that the bone of the living fish’s skull can be exposed – a condition known as the ‘death crown’.

Wild salmon get rid of the lice naturally, because they drop off when the fish migrate into freshwater. Mature wild salmon also have a covering of mucus that repels the lice. 

Farmed salmon, crowded in their tens of thousands in a single cage, don’t have these advantages.

The large number of salmon contained in cages allows sea lice to multiply substantially. Wild salmon range over a wide area, thereby minimising the opportunity for sea lice to find hosts and then to reproduce.

This reproduction is further enabled by the proximity of several salmon farms in an area. The lice which breed on the farmed salmon also spread to wild fish causing problems for both welfare and wild fish numbers.

I have always argued that sea lice infestation should be controlled by keeping the fish in much better conditions rather than relying on routine treatment.

As well as making sure that fish are kept less intensively, the numbers of salmon farmed in an area should be limited to prevent build-up of lice. All the salmon farms in that area should be periodically and simultaneously fallowed to break the cycle.

The thermolicer appears to be a brutal treatment which has not been subjected to a full and proper welfare assessment. It involves a series of steps which are inherently stressful and will cause poor welfare to the fish.

Improved design and management could reduce this stress but cannot be expected to eliminate it.

Any treatment system should be subjected to properly conducted welfare analysis before its use is permitted.

Having taken a close interest in the welfare of farmed fish for over 25 years now, I am shocked anew by these latest reports.

I call on the industry to abandon such heat-shock methods in favour of better rearing conditions for the fish. And the sooner the better.


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Compassion in World Farming campaigns to end factory farming. My new book, Dead Zone, explores the links between factory farming and the demise of our iconic wildlife, and what we can do to save it.

Philip Lymbery

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You wouldn’t know that this is going on… you wouldn’t know that it’s part of industrial farming