Food safety advice on fish parasites for anglers and other fishing enthusiasts who may want to eat their own catch of Atlantic salmon and sea trout.

Atlantic salmon and sea trout caught at sea or in UK rivers are known to be at risk of being infected with parasitic worms, including larvae of the anisakis species.

Health risks to consumers

Parasites in fish, particularly anisakis larvae, can cause health problems if eaten alive, including abdominal pain, diarrhoea and vomiting, blood and mucus in stools, and mild fever.

Allergic reactions can also occur, which may be accompanied by a rash and itching, and even anaphylaxis in rare situations.

Anisakis larvae are colourless and normally coiled like a spring within a cyst. Larvae range in size from 5mm to 20mm in length.

The Food Standards Agency has issued the following advice for anyone eating wild Atlantic salmon or sea trout privately caught at sea or from UK rivers:

Remove the guts

Anisakis larvae can be present on the surfaces of tissues around the internal organs and guts of the fish.

Remove the guts and inspect the body cavity and muscle walls. Remove all visible parasites.

In most cases, especially in salmon, the parasite may also be found within the muscles, especially in those that surround the body cavity and the anus (the vent).

Check the muscle surrounding the anus, particularly if the fish have red and swollen vents.

Freeze before eating

If wild fish are to be eaten raw or lightly cooked, ensure that all parts, especially the thickest part, has been frozen for at least four days in a domestic freezer at -15C or colder. This will ensure that any undetected anisakis larvae are killed.

Where whole large fish, or very thick parts of unfilleted fish, are frozen, it may take some time for the thickest parts of the fish to get down to this temperature after placing in the freezer.

In such cases, it is advisable to freeze for five days or longer to ensure that a low enough temperature is maintained right through the fish for at least four full days.

This freezing advice also relates to wild caught fish that are to be cold-smoked, or eaten after marinating or salting.

Cook thoroughly

When hot-smoking wild caught fish (ensuring the temperature at its thickest point reaches above 60C for at least one minute), the flesh of the fish should be steaming hot throughout after smoking and generally have a flaky texture. This cooking process will kill any anisakis larvae present.

Where it is not possible to freeze the fish properly, and other cooking processes are used, make sure the fish is cooked thoroughly and is steaming hot in the middle.

You can also use a food thermometer or probe to test the temperature in the centre of the piece of fish.

Although cooking at a core temperature above 60C for at least one minute (as for hot-smoking) is sufficient to kill anisakis larvae, it is generally recommended to cook fish at its thickest point at 70C for two minutes. This is to ensure that illness-causing bacteria (such as listeria monocytogenes) that may be on the fish are also destroyed.

Shop-bought fish

Controls are in place to ensure that the presence of parasites in fishery products purchased in a shop is kept to a minimum.

Food businesses that sell fishery products are required to visually examine the fish to check for parasites and they must not sell the products if they are obviously contaminated with parasites.

In addition, unless the fishery product meets exemption requirements, all fishery products that are to be consumed raw or lightly cooked (for example, sushi), marinated, salted or subjected to other treatments are required to undergo a freezing treatment to kill any parasites.