How to buy sustainable fish

Fish is high in protein, low in fat and, if it's oily, high in omega 3 and micronutrients. The NHS advises us to eat at least two portions of fish a week. 

But in the UK we can be unadventurous in our seafood choices; 80% of the fish we eat comes from just five species – cod, haddock, prawns, salmon and tuna. 

We asked Which? members about their seafood habits and found that 56% regularly bought salmon and 42% cod. Prawns, haddock and tuna follow behind. Mackerel (18%) and sea bass (16%) were the next most regularly bought.

Reliance on this small number of varieties places pressure on wild fish numbers or can lead to unsustainable farming practices. 

Why change our seafood choices?

The Marine Stewardship Council (MSC) says a third of global fish stocks are now fished beyond sustainable limits, impacting global food security. 

Losing species is about more than just loss of biodiversity. The ocean depends on resilient ecosystems to keep performing its role as a carbon sink (about a third of the carbon we create is stored in the ocean). And a recent study calculated that bottom trawling fishing methods could be disturbing up to one gigaton of carbon a year, more than aviation emissions, although more research is needed.

Farmed fish account for more than half the fish consumed globally, and aquaculture, or fish farming, is sometimes seen as a more sustainable option. But it comes with its own environmental issues. Some farming methods have negative impacts on the environment, and carnivorous species such as salmon and prawns require wild-caught fish in their diet which puts pressure on these fish stocks.

How to prevent overfishing

As a general rule, smaller fishing boats often have environmental advantages over larger ones. 

Smaller, in-shore vessels tend to use passive fishing gear such as pots, traps and fixed nets with less environmental impact. Rather than stopping fishing altogether, one approach is to favour these low-impact methods and create strategically placed marine protected areas (MPAs), to safeguard sensitive habitats and breeding and nursery areas.

The aim is to protect 30% of the world's oceans in MPAs or marine reserves by 2030. This is ambitious: currently only around 7% of the ocean is under some form of marine protection, according to the International Union for the Conservation of Nature (IUCN). Only 1.89% of these are 'no take' MPAs, where no fishing or other extractive activities can take place.

Greenpeace is campaigning for a ban on all destructive industrial fishing vessels in UK MPAs. In 2021, vessels with bottom-towed gear spent an estimated 47,833 hours fishing in UK offshore MPAs. According to the MSC, bottom trawling can be done sustainably but must be well managed and should be avoided in vulnerable areas.

Sustainable labels to look out for

​​​​What to look for on the label

If you're buying packaged, uncooked and unprocessed fish, the pack must give you information about the place and method of catch.

This isn't required for fish that has been processed, such as fishcakes or fish fingers.

To find out more about methods of catch and the different environmental impacts they have visit the Marine Conservation Society.

Most UK supermarkets are signed up to the Sustainable Seafood Coalition, which includes rules around labelling. The word ‘responsibly’ will either mean the product is farmed (farmed products can’t be ‘sustainable’) or from a wild source that has been risk assessed. 'Sustainably’ sourced means the fishery is accredited by an independent certification scheme.

Here are some certification labels that you might see.

Aquaculture Stewardship Council – ASC

An independent certification for farmed fish covering legal, environmental and social criteria. There are currently 11 different standards for 17 different species of fish and seafood.

There's also a feed standard to make sure what is fed to aquaculture is responsibly sourced.

Global G.A.P.

A business to business standard for the certification of agricultural goods, which includes environmental care, welfare and workers’ health and safety. 

Global G.A.P. does also have a consumer label called the GGN. Consumers can search a unique 13-digit number found on the packet on the GGN label portal to find a profile for the corresponding farm or business.

This packaging logo isn’t that widespread in the UK so fish may well be certified without consumers being aware – supermarket fish is often certified to this or the Global Aquaculture Alliance's BAP scheme.

Global Aquaculture Alliance – Best Aquaculture Practices (BAP)

The BAP logo is more common in the US. Standards cover environmental responsibility, animal health and welfare, food safety and social responsibility. 

Each stage of the production process (farms, processing plants, hatcheries and feed mills) must pass certification to achieve a star – ideally choose 4* certified products.

Soil Association Organic

Farmed seafood certified organic will generally have less environmental impact as fewer chemicals and medicines are allowed. Stocking densities tend to be lower, which the Soil Association says can reduce stress, and the risk of disease and parasites. 

The first choice for feed is usually by-products of fish otherwise destined for human consumption and organic plant-based feed. Whole fish feed (wild fish) must be justified as necessary for fish health and welfare.  

There are also other organic certification schemes, such as Organic Farmers and Growers (OF&G).

Marine Stewardship Council – MSC

The MSC blue tick requires wild-caught fish to come from a fishery assessed as sustainable. This means only fishing from healthy stocks, keeping the stocks well-managed and minimising the impact of fishing on other species and the ecosystem. 

Sustainable fisheries must have measures in place to reduce 'bycatch' – fish caught unintentionally. Bycatch is different fish than the main catch, but can also be protected species such as whales, dolphins and sea turtles that get caught up in fishing gear.

In 2023 MSC-labelled products accounted for nearly 60% of UK seafood retail sales.  

Atlantic cod, walleye pollock, and haddock are the three most sold MSC species in the UK and Ireland by some quantity.

While any size of fishery can be MSC-certified, costs and paperwork can be barriers to entry for smaller operations. Many UK fisheries are also ’data deficient’, meaning they don‘t have enough scientific information on fish populations and environmental impact to pass an assessment. This means that while MSC is a good option to go for where it exists, not all uncertified fish is unsustainable. 

The MSC facilitates Project UK – a partnership of UK fishery improvement projects (FIPs) to encourage sustainability of fisheries that aren’t yet certified.

Fish swaps

If you're prepared to broaden your culinary horizons, there are plenty of local seafood options you can choose to improve your eco-footprint while eating seafood. Sustain, an alliance for better food and farming, and the MCS give advice below on recommended swaps.

While buying UK fish in many cases is a good idea and the British industry should be supported where possible, this is not always the case. Transport is usually a relatively small part of the overall environmental footprint of fish. Sustainable fish from abroad can be better than unsustainable, over-fished local fish.

Salmon

The majority of salmon in the supermarkets will be Atlantic salmon and is farmed, mainly in Scotland, though some will be from Norway.

Issues with salmon farming highlighted by campaigners are around feed (they're fed wild fish), pollution caused by their waste and pesticides, and the parasites they can spread to local fish populations, such as sea lice. 

The industry is working on innovations to improve the environmental impact of farms, but environmental campaigners, including the Marine Conservation Society, say planned expansion of the salmon farming industry needs to be paused until these issues are tackled.

All Scottish salmon is RSPCA-assured, a standard that ensures certain welfare requirements are met, including humane slaughter, but doesn't cover all the environmental issues.

If you really want to eat farmed salmon, the best choice according to the Good Fish Guide, is ASC-certified salmon or organic. Organic salmon is fed largely on feed made from waste trimmings. In practice, this means far less wild-capture fish is used. Organic farming can also help to mitigate against some of the environmental impacts.

Wild Pacific Sockeye Salmon (from Alaska) is a good option, but avoid wild Atlantic salmon as stocks are at historically low levels.

Swap salmon for...

UK rainbow trout are less intensively farmed, and because they're farmed in ponds they tend to have less environmental impact than fish farmed in open-net pens. They still need to be fed wild fish, though. Eating vegetarian fish such as tilapia removes this issue.

UK brown crab Salmon is known for its high omega-3 content but it certainly isn't the only fish or shellfish source. The Shellfish Association of Great Britain says 100g of crab contains 45% of your weekly amount of Omega-3. The most sustainable method of catch is through pot or creel, as this selects larger crabs and has minimal impact on the surrounding environment. 

Alternatively, get your omega-3 by eating what salmon eat. Oily fish including herring, anchovy and sardines are high in micronutrients. Dense-schooling fish like these lessen the carbon emissions involved in wild fishing as boats don't have to travel as much for a haul – they can catch large numbers all at once.

Warm water prawns or shrimp

Big tiger or jumbo prawns (also known as shrimp) are found in warm water and can be farmed, commonly in South-East Asia, or wild-caught. 

Wild-caught prawns are bottom trawled, which damages the seabed and can pick up huge amounts of marine creatures and fish caught unintentionally (bycatch).

Farmed prawns were historically associated with the destruction of mangrove forests, although there are now some projects attempting to reforest mangrove forests alongside shrimp farming. Studies have indicated mangrove forests can store four times as much carbon as tropical forests. Shrimp farms have also been associated with human rights abuses. 

Like salmon, prawns require fish protein in their feed and a proportion of this comes from wild-caught fish. 

The Good Fish Guide says choose organic or ASC prawns – part of the ASC standards include farms demonstrating they're treating workers fairly.  

Swap warm water prawns or shrimp for...

Cold water prawns The best bet is to avoid warm-water prawns, opting instead for cold-water, wild-caught, MSC-certified prawns, typically from the waters between Canada and Norway. They are also harvested by bottom trawling, but in areas of muddy sediment, where the lasting environmental impact is lessened and bycatch is less of an issue.

Pot-caught UK langoustines (also known as Dublin Bay prawns or scampi) are fished with very little impact on the environment and are part of a UK Fisheries Improvement Project (FIP). 

Rope-farmed mussels have some seriously impressive sustainability credentials – they take their nutrients from the sea water and, at the same time, filter and clean it, actively sequester carbon into their shells, and are full of micronutrients and high levels of Omega-3. Rope farming means harvesting them does no damage to the sea bed.

Tuna

Tuna is often fished in the High Seas, the international waters that make up around two-thirds of our oceans. Monitoring and controlling activities in these waters is challenging and the Environmental Justice Foundation and other campaigners have uncovered human rights abuses and slavery.

Some tuna is more sustainable than others. Skipjack and Albacore are usually the best choices but it does depend on fishing methods. Some brands and supermarkets will clearly label their tuna as caught by pole and line – this, handline and troll-caught (another type of line fishing) are generally viewed as the most sustainable. 

Avoid tuna caught by gillnet as these nets can be up to 7km long and have high levels of bycatch.

Most Pacific or Southern Bluefin tuna stocks are at critical levels.

Swap tuna for...

UK mackerel is a good nutritional substitute when fished locally. All mackerel in the northeast Atlantic lost MSC certification in 2019 after stocks dropped below a precautionary level and country catch quotas were deemed too high. But UK mackerel, mainly from Cornwall, caught by boats using handlines is a good choice.

Sardines, another oily fish high in Omega-3, can also be fished locally. 

Cod

Cod was once the cautionary tale of overfishing – the 90s saw a collapse in Atlantic cod stocks. Impressive efforts to rebuild those stocks mean that you can now buy sustainable cod, but it's worth noting that this won't be from the UK – most of the MSC-certified cod you'll find in the supermarket comes from Iceland or Norway.

There are some good white fish alternatives that you can look out for.

Swap cod for...

Hake can be fished sustainably from the UK.

Coley from Iceland and the North-East Arctic is also a good choice, and is often cheap to buy. MSC-certified is the best option.

Pollock sustainability varies, but there are some good choices from Alaska and parts of Russia.

Or try haddock.

Haddock

The UK's haddock stocks are in a reasonable state. Much of what’s in the supermarket will be MSC-certified.

Methods of catching haddock can mean there is some bycatch, so where it's fished can have an impact. The Cornwall Good Seafood Guide says you can protect juvenile fish by only buying fish that are larger than 30cm and avoiding buying fresh haddock during their main breeding season – March and April.

Swap haddock for...

You don’t need to avoid eating haddock. But, as with cod, hake, coley and pollock are good substitutes.

Buying from a supermarket

You can find out more about the supermarkets’ sustainability commitments using the Ocean Disclosure Project – this database/website collates information voluntarily supplied by the retailers on all their own-brand seafood.

The website tells you how much of each supermarket's range is certified. For farmed fish these must be ASC, BIM (Irish certification) BAP (at least two star) or Global GAP, and for wild fish it must be MSC or a small number of other country-specific certifications. It also recognises fisheries that are part of a Fisheries Improvement Project (FIP). It doesn't view organic as a sustainability certification.

Using FIPs as suppliers should be acknowledged as supermarkets helping to drive improvement. An FIP will not have the same sustainability credentials as a certified fishery but will be working towards a sustainability certification.

Buying from a fishmonger or online marketplace

Generally, buying from a fishmonger (or supermarket fish counter) means you can ask for more information about where and how the fish was caught.

The same information that's mandatory for packaged fish should be readily available (displayed somewhere in the shop), but your fishmonger may also have extra details and/or may be able to suggest interesting alternatives to your normal choice.

If you aren't sure about the provenance of something, use the Good Fish Guide. Created by the Marine Conservation Society, the app (and website) gives detailed information about global fisheries for every species you're likely to find in the shops or on your plate. It uses a traffic light rating system, where green equals best choice and red means avoid. 

Often the most sustainable choice will also be MSC-certified, but there are good uncertified choices and using the Good Fish Guide will help identify them.

Online marketplaces such as Pesky Fish, Sole of Discretion and Sole Share can be a good way to try different seafood that's sourced directly from small fisherman. Some are designed for one-off purchases, others are subscription-based, but they tend to be focused on locally caught British seafood and offer a diverse range of fish.