Anisakis spp. - Red/bleeding vents in salmonids

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10th October 2007 - Guidance for Anglers catching fish with bleeding vents

The Trust has been following up concerns relating to the increasing number of fish being caught with bleeding vents on the Tyne. As many anglers are aware this is caused by the worm-like parasite Anisakis. Fish become infected by eating infected crustaceans whilst at sea and some recommendations have been made by various bodies regarding their treatment and consumption by anglers.

What is Anisakis?
What do infected fish look like?
What to do if you catch an infected fish - catch and release questions?
Can you safely to eat an infected fish?
I have caught an infected fish in the Tyne and wish to report it

What is Anisakis?

Information taken from the Wikipedia entry for Anisakis

Anisakis is a genus of parasitic nematodes, which have a life cycle involving fish and marine mammals. They are infective to humans and cause Anisakiasis, and fish which have been infected with Anisakis spp. can produce an anaphylactic reaction in people who have become sensitized to Immunoglobulin E (IgE). The life cycle of the nematode is completed when a marine mammal eats the infected fish and itself become infected. As the gut of a marine mammal is functionally very similar to that of a human, Anisakis spp. are able to infect humans who eat raw or undercooked fish.

Picture of the nematode parasite

To find out more visit these sites:

What do infected fish look like?

Infected fish have reddened and often bleeding vents on the underside of their bodies.

The picture below shows a swollen vent due to Anisakis spp. Picture courtesy of Rob Evans from the Environment Agency.

Reports from the Tamar suggest that this problem has not been observed or known about for 2 years. They had a similar condition last year which was believed to be Vibriosis spp that affects stressed fish in warm water temperatures. It was particularly present in fish held up in the estuary under low flows. A small number of fish were subsequently found dead in freshwater. However the incidence of mortality and infection was low.

None of the fish reported to the Tamar group last year had high parasite loadings and anglers did not report any issues with parasites in fish to us. In comparison, 80% of Tamar trapped grilse this year have this problem. The condition appears to be widespread and has been reported in many salmon rivers in England and Wales, including the rivers Exe, Dee, Taff, Camel, Tamar Eden, Tyne, Itchen, Ribble, Esk, Exe, Wye and Lune, and in a number of Scottish and Irish rivers.

To find out more view the January 2007 report from Rob Evans Environment Agency Head Office Policy and Process (Salmonids and Marine).

What to do if you catch an infected fish - catch and release guidelines

The Trust has received some limited advice for anglers.

all salmon without swollen vents induced by Anisakis spp infection should be returned to the river on the basis that fish with undamaged vents are far more likely to be able to spawn successfully than those that are infected. It seems sensible and prudent to maximise the potential spawning success of unaffected fish at this time owing to the unknown impact that this condition may have on salmon reproductive success.
Salmon that are infected can be retained or returned depending on personal preference - there is no official guidance on the spawning potential for infected fish. The Trust would encourage anglers to use their judgement in the event of catching an infected fish and, if they do choose to keep it to eat - follow the guidance from the FSA set out below.

Can you safely to eat an infected fish?

If you do wish to keep your catch these guidelines have been issued by the Food Standards Agency.

Guidance concerning Wild Salmon and the Anisakis parasite

It has come to our attention that there has been an increased prevalence of wild salmon in UK rivers infected with the parasite Anisakis. We are therefore providing this Food Standards Agency (FSA) guidance for those anglers and netsmen who may want to eat their own catch or supply small quantities to local retail establishments or members of the general public.

A raft of hygiene legislation sets out extensive legal requirements for food businesses that place fishery products on the market for human consumption. However, these requirements do not have force over the preparation and handling of food for ‘private or domestic’ use, or where small quantities of primary products are supplied to final consumers and local retail establishments. The catching of wild salmon from UK rivers for personal or local consumption falls into these categories. Consequently the FSA are advising consumers of about hygiene practices to ensure that these products are safe to eat.

Parasites in fish, particularly anisakis, can, if ingested alive, cause serious health problems. Therefore the FSA recommends that anyone consuming wild salmon taken from UK rivers adheres to the following advice:

Visually inspect the wild salmon to detect and remove parasites. Those fish which remain obviously contaminated should not be consumed.
If wild salmon is to be eaten raw or almost raw it should be frozen in all parts for at least 24 hours, at a temperature of -20°C or colder. This will ensure that any non-visible parasites or undetectable larvae of nematodes are destroyed.
This freezing advice also extends to wild salmon that are to undergo a cold smoking process or to be eaten after marinating or salting i.e. as in Gravadlax.
Where wild salmon is to be hot smoked (internal temperature above 60°C), which is sufficient to kill any parasites present, then it is safe to eat without freezing first.
Where it is not possible to carry out adequate freezing it is advisable to cook the wild salmon. A temperature of 70°C for two minutes will kill any parasitic contamination present. As there is no infallible method of detecting and removing larvae, this advice is particularly relevant for pregnant women and elderly people, where ingestion of live parasites from fish could pose a serious health risk.

This guidance has been issued by the Fish and Shellfish Hygiene Branch, which is part of the FSA's Primary Production Division. To discuss or seek further clarification please contact Mr Michael Talbot on 0207 276 8991 or by email to This e-mail address is being protected from spambots, you need JavaScript enabled to view it