Fish food poisoning

The most common cases of food poisoning which involve fish usually occur as a result of eating contaminated prawns or other shellfish. A good example of this is oysters which some people enjoy consuming whilst raw.

But these often contain bacteria which are likely to cause food poisoning and other similar conditions.

These fish filter seaweed or algae from the water surrounding them but bacteria live in this water and enter the fish during their filtration process. These bacteria then take root inside the fish.

It is easy to think of food poisoning as something which you get if you eat contaminated chicken, beef or pork but unfortunately, it includes fish as well.

There are two types of fish food poisoning which are:

• Ciguatera poisoning
• Scombroid poisoning

Both of these are discussed as individual subsections within this guide.

Fish as part of a healthy lifestyle

Fish is good for us and we are encouraged to include it as part of a healthy diet. In particular, oily fish which contains high levels of omega 3 fatty acids which are good for ‘heart health’.

There is a wide range of fish to choose from and experts recommend that we eat at least a couple of portions a week.

But as with anything in life, moderation is the key.

Girls and women are advised to eat no more than 2 portions of oily fish a week due to the presence of pollutants within the fish which can build up in the body over time.

So, if a girl or woman decides to have a baby at some point in the future then these pollutants may affect its development.

Another problem and one which applies to adults of both sexes is that of high levels of mercury within certain types of fish. Swordfish, marlin and shark contain mercury and it is advised that people limit their consumption of these to one portion only each week.

The Food Standards Agency website (www.food.gov.uk) contains useful advice about the amount and types of fish you can eat.

That is the healthy side of fish but there is downside which is food poisoning.

Fish and food poisoning

So what can go wrong?

The same rules about food safety and preparation apply to fish as with any other food product. If fish is left out on a work surface for any period of time then it will decay (or ‘go off’) very quickly.

Raw and cooked fish must not come into contact with each other due to the risk of cross contamination. This means using separate utensils and chopping boards for raw and cooked fish and wiping them down after use.

Fish needs to be cooked thoroughly and at the correct temperature.

One exception to this is sushi. Sushi is a popular Japanese dish which consists of raw fish, e.g. salmon, rolled in rice and seaweed. This is available in restaurants and as ready prepared packs in supermarkets.

Generally, this is safe to eat as long as the fish used has been cooked or if raw, has been frozen beforehand in order to kill off any parasites.

Causes of fish food poisoning

This type of food poisoning is caused by fish which has been contaminated by:

• Parasites
• Toxins
• Bacteria, e.g. E coli
• Viruses, e.g. norovirus

Fish which can be eaten raw such as oysters or mussels are always a risky choice as well as being a likely candidate for food poisoning. So, if you enjoy the taste of oysters, especially a raw one then be aware that the odds of getting food poisoning are quite high.

Parasites

Food poisoning caused by parasites is rare, especially in countries such as the UK. It occurs as a result of eating raw fish which has been contaminated with any of the following parasites:

• Clonorchis sinensis
• Anisakis
• Diphyllobothrium

(Source: Centers for Disease Control and Prevention)

These are all names for different types of ‘fish tapeworms’ which enter the gastrointestinal tract during consumption. Once there they cause a range of problems which includes abdominal pain, nausea, vomiting and diarrhoea.

Toxins

There is a wide range of toxins present in seawater which are produced by any number of agents such as marine plankton and algae. These are capable of a range of health problems such as ciguatera poisoning although this is uncommon.

Find out more in our shellfish toxins section.

Bacteria

A well known example of this is E coli. This bacterium is present in nearly all types of shellfish as a result of contact with water contaminated by raw sewage.

Find out more about E coli in our bacterial food poisoning section.

Viruses

The virus in this case is the norovirus which is spread via contaminated food and water, and personal contact with someone who is already infected.

There are two types of foods which often cause an outbreak of the norovirus: salads and shellfish. In the latter case it usually occurs due to insufficient heating of shellfish before consumption.

Find out more in our viral food poisoning section.

Symptoms of fish food poisoning

These are similar to symptoms for other types of food poisoning and include:

• Nausea
• Vomiting
• Diarrhoea
• Upset stomach
• Stomach pains
• Muscle/joint pains
• Headache

These symptoms develop within 48 hours of eating contaminated fish.

The severity of these symptoms will vary between individuals. Some people will have a much worse experience than others which may depend upon how much contaminated fish they have eaten.

There are groups of people who for a variety of reasons, are at a greater risk of getting this type of food poisoning. These include people with a poorly functioning immune system, are currently suffering from a medical condition or work in an environment where they handle raw fish.

If any of this applies to you then take a few extra precautions to reduce the risk of this happening.

Treatment for fish food poisoning

This depends upon the extent of your illness. If your food poisoning is relatively mild then you can treat it at home. This means bed rest and plenty of liquids.

If you are worried about the risk of dehydration then replace any essential vitamins and minerals lost as a result of your food poisoning. Drink plenty of fluids, e.g. water but add a sachet of re-hydration salts to it which will replace these as well as ensuring that you are properly hydrated.

Dehydration is a major risk of food poisoning and is something to avoid if possible. But if you do become dehydrated then you will require hospital treatment.

This means re-hydration via an intravenous drip.

If you developed ciguatera or scombroid food poisoning as a result of eating contaminated fish then the treatment for that is discussed within that section.

Preventing fish food poisoning

Can you prevent yourself from getting food poisoning from fish?

You can reduce the likelihood of this happening by applying a few common sense measures. These include:

• Ensuring fish has been properly cooked or if eaten raw (e.g. sushi) has been frozen beforehand.
• Do not store fish especially shellfish in water
• Separate raw fish from cooked fish
• Wash your hands before and after handling fish. Also wipe down any chopping boards, utensils and kitchen worktops afterwards.
• Store fish in the fridge as soon as possible after purchase

These and other measures are discussed in greater detail in our preventing food poisoning section.