Fish and shellfish

A healthy diet should include at least two portions of fish a week, including one of oily fish.

That's because fish and shellfish are good sources of many vitamins and minerals. Oily fish – such as salmon and fresh tuna – is also particularly high in long-chain omega-3 fatty acids, which may help to keep your heart healthy.

Most of us should have more fish in our diet, including more oily fish. However, there are maximum recommended amounts for oily fish, crab and some types of white fish. There is additional advice for women who are pregnant or breastfeeding, and children and babies.

Fish that is steamed, baked or grilled is a healthier choice than fried fish. Frying makes fish and shellfish much higher in fat, especially if they’re cooked in batter.

To ensure there are enough fish to eat now and in the future, we should try to eat a wide variety of fish and to buy fish from sustainable sources.

Click on the links below for more information about incorporating fish into your diet.

Types of fish
Oily fish and omega-3 fatty acids
How much fish should adults and children eat?
Taking fish liver oil supplements
Eating sustainable fish and shellfish
Fish and shellfish safety
Buying fish and shellfish
Catching fish and shellfish
Storing fish and shellfish
Preparing fish and shellfish
Fish and shellfish allergy

Types of fish

Different types of fish and shellfish provide different nutrients.

Oily fish

Salmon, mackerel, sardines, trout and herring are all examples of oily fish. Oily fish are:

  • high in long-chain omega-3 fatty acids, which may help prevent heart disease
  • a good source of vitamin D

Some oily fish contain bones that you eat. These include whitebait, canned sardines, pilchards and tinned salmon (but not fresh salmon). These fish can help keep our bones strong because they are good sources of calcium and phosphorus.

White fish

Cod, haddock, plaice, pollack, coley, dab, flounder, red mullet, gurnard and tilapia are all examples of white fish. 

White fish are:

  • low in fat, making them one of the healthier, low-fat alternatives to red or processed meat, which tends to be higher in fat, especially saturated fat
  • a source of omega-3 fatty acids, but at much lower levels than oily fish

Shellfish

Shellfish includes prawns, mussels, scallops, squid and langoustine. 

Shellfish are:

  • low in fat
  • a source of selenium, zinc, iodine and copper

Some types of shellfish, such as mussels, oysters, squid and crab, are also good sources of long-chain omega-3 fatty acids, but they do not contain as much as oily fish.

Oily fish and omega-3 fatty acids

Oily fish contains a special kind of fat, called long-chain omega-3 fatty acids.

Long-chain omega-3 may help prevent heart disease. It is also important for women who are pregnant or breastfeeding because it can help a baby's nervous system to develop.

Which fish are oily fish?

These fish are all oily fish, and so are good sources of long-chain omega-3:

  • anchovies
  • carp
  • herring (bloater, kipper and hilsa are types of herring)
  • jack (also known as scad, horse mackerel and trevally)
  • mackerel
  • pilchards
  • salmon
  • sardines
  • sprats
  • trout
  • tuna (fresh)
  • whitebait

Canned tuna does not count as oily fish. Fresh tuna is an oily fish, but when it is canned the amount of long-chain omega-3 fatty acids is reduced to levels similar to those in other fish.

Oily fish are the richest source of long-chain omega-3. Some white fish and shellfish also contain long-chain omega-3, but not as much as oily fish. The main shellfish sources of long-chain omega-3 are mussels, oysters, squid and crab.

How much fish should we eat?

A healthy diet should include at least two portions of fish a week, including one of oily fish. Most of us aren't eating this much.

But for certain types of fish there are recommendations about the maximum amount you should eat.

How much oily fish should I eat?

We should eat at least one portion (around 140 grams when cooked) of oily fish a week.

Oily fish can contain low levels of pollutants that can build up in the body. For this reason there are maximum recommendations for the number of portions we should be eating each week. These recommendations are different for different groups of people.

  • Women and girls should eat no more than two portions of oily fish a week if they may become pregnant in future or if they are currently pregnant or breastfeeding. This is because pollutants found in oily fish may affect the development of a baby in the womb in the future.
  • Men and boys, and women and girls who know they won't become pregnant in future, can eat up to four portions of oily fish a week.

Who can eat swordfish

Even though swordfish is an oily fish, there is separate advice about how much of it you should eat.

 

Children, pregnant women and women who are trying to become pregnant should not eat swordfish. Other adults should eat no more than one portion of swordfish per week.

This is because it can contain more mercury than other fish, and consuming high levels of mercury can cause health problems.

How much white fish should I eat?

White fish include cod, haddock, plaice, pollack, coley, dover sole, dab, flounder, red mullet and gurnard.

You can safely eat as many portions of white fish per week as you like, except for the following, which may contain similar levels of certain pollutants as oily fish:

  • sea bream
  • sea bass
  • turbot
  • halibut
  • rock salmon (also known as dogfish, flake, huss, rigg or rock eel)

Anyone who regularly eats a lot of fish should avoid eating these five fish, and brown meat from crabs, too often.

Even though shark and marlin are white fish, there is separate advice about how much of them you should eat:

  • Children, pregnant women and women who are trying to get pregnant should not eat shark or marlin. This is because they contain more mercury than other fish.
  • Other adults should have no more than one portion of shark or marlin per week.

Many shark and marlin species are endangered, so we should avoid eating these fish to help stop these species becoming extinct. See the sustainable fish and shellfish section below for more information.

How much shellfish should I eat?

Although it is recommended that regular fish-eaters should avoid eating brown crab meat too often, there is no need to limit the amount of white crab meat that you eat. There are no maximum recommended amounts for other types of shellfish.

Eating fish while trying to get pregnant, and during pregnancy and breastfeeding

Eating fish is good for your health and the development of your baby. But pregnant women should avoid some types of fish and limit the amount they eat of some others. This is because of the levels of mercury and pollutants that some fish can contain.

When pregnant, you can reduce your risk of food poisoning by avoiding raw shellfish and making sure that any shellfish you eat is cooked thoroughly.

Below is advice from the Scientific Advisory Committee on Nutrition and the Committee on Toxicity about eating fish when trying to get pregnant, or when pregnant or breastfeeding:

  • Shark, swordfish and marlin: do not eat these if you are pregnant or trying to get pregnant. All other adults, including breastfeeding women, should eat no more than one portion per week. This is because these fish can contain more mercury than other types of fish, and this can damage a developing baby’s nervous system.
  • Oily fish: if you are trying for a baby, pregnant or breastfeeding, you should have no more than two portions of oily fish a week. A portion is around 140 grams.
  • Canned tuna: if you are trying for a baby or are pregnant, you should have no more than four cans of tuna a week. This is because tuna contains higher levels of mercury than other fish. If you are breastfeeding, there is no limit on how much canned tuna you can eat.

These figures are based on a medium size can of tuna with a drained weight of around 140g per can. Remember, canned tuna doesn't count as oily fish, so you can eat this as well as your maximum two portions of oily fish a week.

Due to the higher levels of mercury in tuna, if you’re eating canned tuna, don’t pick fresh tuna as your oily fish.

Unless your GP advises otherwise, avoid taking fish liver oil supplements when you’re pregnant or trying for a baby. These are high in vitamin A (retinol), which can be harmful to your unborn baby. Pregnant women are advised to avoid taking supplements that contain vitamin A.

Learn more in Have a healthy diet in pregnancy and Foods to avoid in pregnancy.

Should children and babies over six months eat fish?

Children under the age of 16 years should avoid eating any shark, swordfish or marlin. This is because the levels of mercury in these fish can affect a child's nervous system.

Avoid giving raw shellfish to babies and children to reduce their risk of getting food poisoning.

Learn more about healthy eating for the under-fives in Your baby's first solid foods.

You can give boys up to four portions of oily fish a week, but it is best to give girls no more than two portions a week. This is because the low levels of pollutants that oily fish contain can build up in the body and may harm an unborn baby during a future pregnancy.

Taking fish liver oil supplements

If you take fish liver oil supplements, remember these are high in vitamin A. This is because fish store vitamin A in their livers. Having too much vitamin A over many years could be harmful.

The Scientific Advisory Committee on Nutrition advises that if you take supplements containing vitamin A, you should not have more than a total of 1.5mg a day from your food and supplements combined. Pregnant women are advised to avoid taking supplements containing vitamin A, including fish liver oil supplements, as too much vitamin A can be harmful to an unborn baby. Learn more in Vitamin A.

Eating sustainable fish and shellfish

When fish or shellfish are caught or produced in a way that allows stocks to replenish and that does not cause unnecessary damage to marine animals and plants, those fish or shellfish are called “sustainable”.

To ensure there are enough fish and shellfish to eat, choose from as wide a range of these foods as possible. If we eat only a few kinds of fish, then numbers of these fish can fall very low due to overfishing of these stocks.

Overfishing endangers the future supply of the fish and can also cause damage to the environment from which the fish is caught.

Learn more about sustainable fish and shellfish, and what you can do to help on GOV.UK: protecting and sustainably using the marine environment.

Fish and shellfish safety

Eating fish or shellfish that is not fresh or that has not been stored and prepared hygienically can cause food poisoning. In this section you can find tips on how to store and prepare fish and shellfish.

Shellfish such as mussels, clams and oysters that are raw or not thoroughly cooked can contain harmful viruses and bacteria that can cause food poisoning. Thorough cooking usually kills any bacteria or viruses.

Most of the shellfish we eat is cooked first, but oysters are often served raw. 

Raw shellfish, particularly oysters, can be a source of viral contamination. A 2011 study funded by the Food Standards Agency (FSA) found that three-quarters of oysters sampled from harvesting beds within UK waters contained norovirus, although in half of these it was only detected at low levels. Currently, these findings do not provide any greater indication of the risk of becoming ill at the point where oysters are purchased and consumed. If you are serving oysters raw, be especially careful when buying and storing them: see below for more advice.

Shellfish can also be contaminated with biotoxins, such as: 

  • paralytic shellfish poisoning (PSP) toxins
  • lipophilic toxins, including diarrhetic shellfish poisoning (DSP) toxins
  • amnesic shellfish poisoning (ASP) toxins

Depending on the type of toxin present, the symptoms of eating contaminated shellfish may include: 

  • nausea
  • vomiting
  • diarrhoea
  • headaches
  • numbness
  • breathing difficulties
  • memory loss
  • disorientation
  • abdominal pain 

Unlike many other hazards, biotoxins are largely heat stable, which means that even if the food is cooked the toxins will not be broken down or removed. Under EU regulations, commercial shellfish is regulated and tested.   

The FSA advises that older people, pregnant women, very young children and people who are unwell should avoid eating raw or lightly cooked shellfish to reduce their risk of getting food poisoning.

Buying fish and shellfish

When choosing fish and shellfish, remember:

  • Buy fish and shellfish from reputable sources.
  • Choose fresh fish or shellfish that is refrigerated or kept on ice.
  • Don't buy cooked or ready-to-eat fish or shellfish that is touching raw fish or shellfish.
  • When shopping, pick up fish and shellfish last and take it straight home. Fish and shellfish go off very quickly once out of the fridge.
  • When buying or cooking live shellfish such as mussels, make sure that the outer shell closes when you tap it. Live shellfish will "clam up" when their shells are tapped.
  • Where possible, buy fish and shellfish from sustainable sources.

Catching fish and shellfish

Is fishing your passion? Like the thought of eating your own fresh catch? First read this food safety advice from the FSA for anglers and other fishing enthusiasts who may want to eat their own catch of Atlantic salmon and sea trout.

If you want to take shellfish from any public waters, it's important that you check local notices or with your local authority that the area isn’t closed. If it is closed, it may be for public health reasons such as high toxin or bacterial or chemical contamination, in which case it would be dangerous to eat shellfish from that area.

Storing fish and shellfish

Follow these hygiene tips when storing fish:

  • Put fish and shellfish in the fridge or freezer as soon as you get home.
  • Make sure that all fish and shellfish are in covered containers. But don’t put mussels, oysters, clams or any other live shellfish into airtight containers, because they need to breathe.
  • Don't store fish or shellfish in water.
  • Discard mussels, oysters, clams or any other live shellfish if their shells crack or break, or if the shells are open and don’t close when you tap them. Live shellfish will "clam up" if their shells are tapped.

Preparing fish and shellfish

Follow these hygiene tips when preparing fish:

  • Wash your hands thoroughly before and after handling fish or shellfish.
  • Don't allow raw fish or shellfish or fluid from live shellfish to come into contact with cooked or ready-to-eat food.
  • Use separate utensils and plates for preparing raw fish and shellfish and other food.
  • Thaw fish or shellfish in the fridge overnight. If you need to thaw it more quickly, you could use a microwave. Use the "defrost" setting and stop when the fish is icy but flexible.
  • If you’re marinating seafood, put it in the fridge and throw the marinade away after removing the raw fish or shellfish. If you want to use the marinade as a dip or sauce, set some aside before it touches the raw fish.
  • Do not eat clams or mussels that do not open when cooked. It is likely that the clam or mussel has died, and that it is not safe to eat.

Fish and shellfish allergy

Allergies to fish or shellfish are quite common and can cause severe reactions.

People who are allergic to one type of fish often react to other types. Similarly, people who are allergic to one type of shellfish, such as prawns, crabs, mussels or scallops, often react to other types.

Cooking fish or shellfish doesn't make someone with a fish or shellfish allergy less likely to have a bad reaction.

Learn more in Food allergy.

Page last reviewed: 19/12/2013

Next review due: 19/12/2015

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Comments

The 4 comments posted are personal views. Any information they give has not been checked and may not be accurate.

demidog said on 30 June 2014

I'm looking for accurate evidence-based advice on how many portions of tinned tuna is safe to eat per week for my family (for adults, children and babies). This says that there is no limit for anyone except pregnant women (limit 4 times per week), but i'v read recommendations for pregnant, nursing and children to avoid tuna, or limit to 2 times a week.

Can you please provide links to the research that this limit of 4 time per week for pregnant women and unlimited for everyone else is based on? Is there systematic reviews showing this to be safe?

Here is an example of what i'v been reading which is different from the NHS recomendations:

'moderate consumption of seafood, roughly two times per week, does not result in clinically significant symptoms. In fact, the reported favorable neurological effects of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), known as “fish oil,” outweigh the neurological risks of mercury toxicity. In infants, on the other hand, even low levels can lead to mental retardation, cerebellar ataxia, primitive reflexes, dysarthria, and hyperkinesis. The risk of fetal brain damage increases when maternal hair reaches levels greater than 10-20 ppm, but developmental delays have been demonstrated with levels as low as 1.6 ppm.[5] For this reason, the current recommendation is that women of childbearing age, pregnant women, and nursing mothers consume no more that 0.1 microgram/kg/day of mercury, and that they avoid high-mercury seafood altogether.[2]'

http://www.clinicalcorrelations.org/?p=5047


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mountainbiker1 said on 16 November 2013

The comment below about Omega 3 EPA and DPA being available from vegetarian sources is misleading. That available from flax seed oil etc. is of a different kind only a small portion of which can be synthesised to the correct kinds. (Ilardi, S, Therapeutic Lifestyle Change 2010)

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nerdywordy said on 03 November 2013

This article ignores all the more recent research, which looks at longer-term effects, and finds no benefits and even increased risk of heart disease, long-term. This increased risk is thought to be caused by the long-term build up of mercury from dead fish.

You don't have to pay people to kill fish, or poison yourself with mercury, to get omega 3. There are now many vegetarian and vegan supplements available that use the most valuable, supposedly "only in fish" forms of omega 3 - DHA and EPA - from laboratory-grown, uncontaminated algae. Algae is where the fish get it from in the first place.

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JohnyR said on 09 March 2012

I am confused. Presumably there is no maximum recommended amount of shellfish per week. In other words you can eat as much shellish as you like (apart from brown carab meat)?

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