Unlike wild salmon, Scottish farmed salmon carries no risk of parasites when eaten raw.
Research by several institutions, reviewed by the European Food Safety Authority (EFSA), studying the available evidence on the presence of parasites in wild and farmed fish concluded that farmed salmon destined to be eaten raw in dishes like sushi does not need to be frozen before consumption.
This is because farmed salmon are exclusively fed strongly heated and processed dry-feed which therefore cannot contain parasites such as Anisakis.
In 2015, the Norwegian Institute of Marine Research examined 4,184 farmed salmon from 37 salmon farms and did not find any Anisakis.
What is Anisakis?
Anisakis is a marine parasitic worm that can be found in certain species of wild fish. It is common in wild salmon, herring and sardines.
Eating raw fish infected with Anisakis could cause anisakiasis, a parasitic infection which can cause stomach pain and nausea.
The illness cannot be transmitted human to human.
How to prevent it
The Food Standards Agency requires for all fish and fishery products to be inspected in order to remove visible parasites before being sold.
They also instruct for fishery products intended to be eaten raw to be frozen before use.
Freezing the fish to a core temperature of minus 20 degrees Celsius for 24 hours or minus 35 degrees Celsius for 15 hours will kill any Anisakis parasites that might be present in the product.
Typical household preparation methods for wild fresh fish, such as frying and poaching or boiling will also kill Anisakis.
However, the Food Standards Agency makes exemptions for farmed fish. As long as embryos have been reared in an environment that is free from parasites and that the food business can verify that the fishery products do not present any health hazards in relation to parasites, farmed salmon does not need to be frozen.