Fish oils are the latest nutritional buzz. Although mothers have for decades been coaxing reluctant children to swallow a daily dose of cod-liver oil, knowing that “fish is good for the brain”, the business has exploded in recent months. In fact, such is our obsession with fish-oil supplements in various forms that we now spend more than £96m a year on them in the UK alone.

Their benefits have been well publicised. Omega-3 fats from oily fish, for example, can help to keep blood flowing smoothly, which lowers the risk of heart disease and stroke. Studies have shown that omega-3s may also help to treat dyslexia and hyperactivity in youngsters. The fats are known to build the foundations of good eyesight and hearing in the unborn and nursing baby. This means that they are, indeed, good for the brain, and a crucial part of the diets of children as well as pregnant and breast-feeding women. Omega-3s also play an anti-inflammatory role in the body and can help to alleviate symptoms of conditions ranging from psoriasis to rheumatoid arthritis. What’s more, they are vital for smooth, well-hydrated skin.

Taking a supplement is one means of meeting your daily omega-3 needs, but the time-honoured way of getting the daily quota, preferred by dieticians, is to eat seafood — one of the best sources. The advice always used to be to tuck into oily fish such as salmon, tuna, mackerel, sardines and anchovies as often as you fancied. But times have changed. Pollution of our waterways, lakes, rivers and oceans is now so commonplace that such a general recommendation needs refining. The flesh of oily fish absorbs pollutants known as polychlorinated biphenyls (PCBs), consumption of which has been linked to the disruption of vital hormones in our bodies and may trigger cancerous changes to cells.

The best way to ensure that you limit your intake of PCBs from oily fish is to choose wild varieties over the farmed versions. The reason for this is that wild fish feed in the oceans, and so their flesh tends to be lower in PCBs than that of farmed fish, such as salmon, which are fed ground fishmeal. Surprisingly, splashing out extra cash on organic farmed fish is no guarantee that you will consume lower levels of these pollutants. What the organic label on farmed salmon does guarantee, however, is that the traditional pink colour of the flesh is achieved naturally rather than by artificial colourings.

Ocean-living oily fish are generally lower in PCBs than those caught in lakes, rivers and streams. The exception is fish from the Baltic, one of the most polluted seas in the world. The only way of knowing where a particular fish has come from is to choose those that carry a label stating their origin, such as Scottish wild salmon or Atlantic sardines.

Whichever type of oily fish you end up with in the kitchen, wherever it comes from and however it is reared, trimming off and discarding any visible fatty parts of the fish helps to reduce PCB levels. So, too, does steaming, baking and grilling, during which oils run off the fish, rather than frying, during which they are retained.

To keep PCB intake at a safe level, women of child-bearing age and children are advised to have no more than two servings of oily fish a week. Men can get away with up to four servings. There are no such guidelines for white fish, however. Non-oily, ocean-dwelling fish, such as cod and haddock, have lean flesh, which does not retain PCBs. They also store fat in their livers, which means that PCB levels in the flesh we eat is kept to a minimum. The same is true of shellfish. These provide smaller, though still useful amounts of omega-3 oils, but they have the advantage of being a great source of protein, of energy-giving B vitamins, and of iodine, a mineral that helps to fine-tune our metabolism.

Unfortunately, eating non-oily fish (or, indeed, other, larger fish) won’t keep you safe from another pollutant — methylmercury. This organic mercury compound is highly poisonous to the nervous system and, if allowed to accumulate in the body, can trigger poor concentration, disturbances in vision, tremors, numbness and tingling. It is especially toxic to unborn babies because it can cause serious damage to their developing brains and spinal cords. Methylmercury accumulates in fish, so the bigger and older the fish, the more of the compound might be contained in its flesh. Levels in some fish, such as marlin, swordfish and shark, are high enough to merit a government health warning.

The Food Standards Agency (FSA) advises pre-menopausal women against eating any form of big fish such as marlin, swordfish and shark. A particular type of large tuna called albacore, which has a white flesh, has similarly high levels, whether eaten fresh or canned, and should also be avoided. However, most of the tuna consumed in the UK has brown flesh and tends to be the skipjack or yellowfin varieties. While you may be tempted to shop for fresh tuna because of its higher omega-3 content, it is higher in methylmercury than the canned version. Because of this, women of child-bearing age and children are advised to stick to a maximum of two servings of fresh tuna a week, but can safely have up to four 170g cans of skipjack or yellowfin. There are no such limits for men.

So what should you shop for? The advice from the FSA is: “Do not rely on fish from one source.” What this means is that you should vary not just the type of fish you eat, but also where it comes from. Follow these guidelines to find out how you can have your fish cakes and eat them.

Some fish are more ethical than others, and some are more delicious, says Sybil Kapoor

Delicious, easy to prepare and good for you — it is hardly surprising fish has become so popular in these health-obsessed times. However, many seafood-loving cooks worry that their actions might aggravate the decline in fish stocks. Luckily, there is a way of easing guilt and improving the lot of marine life: you just need to know which fish are endangered and which you should choose instead. The options range from farmed fish to sourcing ethically caught fish. The latter include fish caught in well-managed waters, with the right tackle, when the fish are in season and not spawning. The best place to get this information is the Marine Conservation Society (order its Good Fish Guide on 01989 566017; £10, including p&p). Then quiz your local fishmonger or supermarket regularly to ensure that both you and they buy only ethically sound fish.

GRIDDLED SCALLOPS WITH SOY AND GINGER SAUCE ON WILTED SPINACH

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