Fish, shellfish and other marine animals have been an important part of the human diet throughout human history, providing vital nutrients and shaping much of our approach to food. The ocean’s incredible diversity has even influenced the evolution of entire societies. Today, as science learns more about how we benefit from eating fish and seafood, there are alarming trends appearing from industrial overfishing, pollution, and dwindling species on the edge of extinction.

For consumers the message is confusing in its complexity. Just what is safe to eat, and what should be avoided for sustainability reasons?

In the following sections we explore these issues, examining different types of fish, how often to eat them, choosing sustainable forms, the dangers of mercury, and finding alternatives for your diet.

Health Benefits

There are many health benefits associated with eating fish and much dietary advice recommends eating one or two portions of fish per week, including at least one portion of oily fish. The reason for this has always been made clear; oily fish is rich in omega-3 fatty acids which can help to keep your heart healthy, reduce the risks and symptoms of disorders such as strokes, diabetes, arthritis, some types of cancer and digestive diseases, asthma and mental decline.

Essential omega-3 fatty acids are not made within our bodies so must be taken as part of our diet. In general, fish is high in protein and relatively low in fat when compared to red meats such as beef. The healthiest ways to cook fish include steaming, baking, poaching and grilling. The Japanese, famously, also support the raw consumption of fish as sashimi and sushi. It’s a cultural trend which has spread across the world and is booming in popularity, aided by its appearance as a healthy diet.


Types of Fish

  • Oily fish contain high levels of long-chain omega-3 fatty acids and vitamins A and D. Types of oily fish include species such as anchovies, carp, herring, jack, mackerel, pilchards, salmon, sardines, sprats, trout and whitebait.
  • The NHS recommends women and girls who may become pregnant in the future, pregnant women and women who are breast feeding should eat no more than two portions of oily fish per week. This is because this oily of fish may contain pollutants that can be harmful to babies in the womb.
  • Boys and men should eat up to four portions of oily fish per week.
  • White fish fleshed fish are very low in fat, particularly saturated fat. They also contain omega-3 fatty acids but in smaller amounts than in oily fish. Types of white fish commonly eaten include species such as cod, haddock, plaice, and Pollack.
  • The NHS states you can safely eat as many portions of white fish per week as you like, although obviously all foods should be eaten in moderation.
  • Shellfish are typically low in fat and a good source of minerals including copper, iodine, selenium and zinc. Types of shellfish commonly eaten include crab, langoustine, mussels and prawns.
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Choosing Sustainably

In the last few decades it has become evident fish populations and marine environments have begun to face extreme pressure as a result of the global fishing industry. The impact this billion dollar industry manifests in two key forms; overfishing faster than the fish population can replenish resulting in population collapse, and harmful fishing techniques that are either destructive (such as bottom trawling) or indiscriminate fishing that kills no-target species (such as dolphins killed during tuna fishing).

Research into the matter has been alarming, many sources indicating human fishing, at current rates, will bring about a global collapse in fish species by 2048. There have been attempts to combat this – since the 1990s there has been a growing interest in sustainability.

Sustainable fishing can be defined as fishing that does not upset the ecological balance of the oceans. Organizations such as the Marine Stewardship Council (MSC) were developed with the aim of conserving the marine life of the oceans. The MSC attempts to regulate sustainable seafood by certifying fisheries according to their practices and marking approved seafood with an ‘ecolabel’.

Consumers should look for the MSC ecolabel when buying fish to help reduce the impact their diet has on the marine environment, although some critics (such as Greenpeace) have pointed out some MSC-certified fisheries  are inadequate. The MSC is working with campaign groups to find a resolution to this problem, as well as regularly updating lists of certified fish to eat on their website, whilst Greenpeace has also produced a list of endangered species which should not be bought:

  • Atlantic cod,
  • Plaice,
  • Tuna,
  • Tropical prawns (wild and farmed),
  • Haddock (except line-caught Icelandic),
  • European Hake,
  • Atlantic Halibut,
  • Monkfish,
  • Atlantic salmon (wild and farmed),
  • Swordfish,
  • Marlin,
  • Sharks,
  • Skates and rays.
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No More Mackerel?

For many years mackerel has been championed as a sustainable fish – tasty and versatile, rich in omega-3 fatty acids, low in fat and, crucially, an abundant and sustainable species. It was therefore a great shock when, in January 2013, the MCS removed mackerel from its certified ‘fish to eat’ list, stating current rates of mackerel fishing are unsustainable.

The EU, locked in a dispute with Iceland over fishing quotas, found mackerel had been increasingly moving North West to the Atlantic waters of Iceland and the Faroe Islands. Both countries have taken advantage of the situation by massively increasing the numbers of mackerel fished, resulting in the unexpected announcement.


The Menace of Mercury

Due to the polluting of the oceans mercury is now prevalent in our seas. Fish and shellfish accumulate mercury within their bodies, usually in the form of methylmercury, an organic compound that is highly toxic for humans. Many fish and shellfish only contain small amounts of mercury so are not harmful if eaten regularly, but certain types, particularly long-living predators higher up the food chain, do contain dangerous levels of the toxin. Due to this it is best to avoid certain species of fish altogether, examples being; blue fin tuna, lake trout, marlin, northern pike, shark, dolphin, swordfish, and tilefish.

Mercury accumulates in the bodies of fish and shellfish by a process of ‘biomagnification’; small amounts of mercury are present in seawater, algae absorb the mercury in the form of methylmercury, fish and other organisms eat the algae, fish eat other fish and organisms containing mercury, and at each stage of the food chain greater amounts of mercury are accumulated. Larger fish eat more small fish and the longer a fish lives the more mercury they can accumulate in their bodies. As a result there are guidelines to fish consumption;

  • The NHS recommends young children, women who are trying to get pregnant, women who are currently pregnant and breastfeeding women should avoid all types of fish that may contain high levels of mercury.
  • All other adults should limit there consumption of this type of fish to a maximum of one portion per week.
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An Alternative Diet

For people who are vegetarians or wish to stop eating fish it is important to ensure essential omega-3 fatty acids are a part of their diet. While fish is recognized as a rich source of these fatty acids, omega-3 is also found in rapeseed oil, flax seeds, walnuts, and small amounts are found in whole milk and eggs. People who avoid eating fish should make sure their diet contains a variety of these foods. The Vegetarian Society also recommends vegetarians who want to increase their omega-3 uptake should take algae or flax seed supplements.


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