WILD salmon in the River Itchen near Alresford are falling prey to a parasite which can be fatal to humans and could deplete salmon stocks. It's estimated that up to 30 per cent of the stock in the world-famous chalk stream is infected with the anisakis simplex parasite, also known as herring worm, which can cause anaphylactic reactions in people. Symptoms include erratic heartbeat and respiratory failure, and can cause death. There is an increasing prevalence of the parasite in rivers across England and Wales. The danger comes when raw or undercooked fish is eaten. The salmon from the Itchen is not eaten, but the Food Standards Agency has issued safety guidelines to people who do eat their own catch from other rivers. If wild salmon is to be eaten raw or almost raw, it should be frozen for 24 hours at -20?C or -4?F to destroy the parasites. This also applies to wild salmon that is to undergo cold smoking or is to be eaten after marinating or salting, for instance, as gravadlax. If not freezing the fish, it should be cooked for at least two minutes at 70C, or 160F. Salmon carrying the parasite should not be eaten. The salmon pick up the parasite when feeding on krill at sea. The parasite causes fish vents to swell and bleed, damaging their ability to spawn.