On the one hand, an international study finds that European farmed salmon contains far more cancer-causing dioxins and PCBs (polychlorinated biphenyls) than wild salmon, and that we should risk no more than one portion a month.

On the other hand, the Food Standards Agency assures us that levels of these contaminants are within safe limits. It advises that we eat one portion of oily fish a week, since “the known benefits . . . outweigh any possible risks”.

Principal among these “benefits” is the essential fatty acid omega-3, vital in the fight against cardiovascular disease. When farmed salmon was first introduced, it was seen as an abundant, affordable source of omega-3, while relieving the pressure on overfished wild stocks. The reality has been different.

FARMED OR WILD?

An intensively farmed salmon contains more fat than its wild cousin, yet less omega-3. It is raised on pellet feed made with fish from the bottom of the North Atlantic, where rivers discharge their chemical cocktails.

On learning this, the obvious response is to turn to wild salmon. But Atlantic salmon is endangered, with stocks down by 50 per cent in the past 20 years thanks in part, ironically, to fish farm contamination. At its worst, a fish farm is a stew of chemicals, parasites, disease and sewage that taints surrounding habitats. Escapees from farms breeding with wild fish may threaten the genetic integrity of wild species. Furthermore, it takes three tons of feed to rear one ton of farmed salmon.

The Marine Conservation Society (MCS) proposes that we favour wild Pacific salmon or responsibly/organically farmed salmon. Wild Alaskan salmon from sustainable stocks and an unpolluted habitat is an appealing option and you can find it in the UK. But consider that it has been air-freighted thousands of miles and you may feel that organic farmed salmon is more environmentally friendly. Well, it is and it isn’t.

ORGANIC?

Friends of the Earth Scotland acknowledge that organic salmon is free from antibiotics and artificial colourings but is concerned that the seas are being plundered for the same fish to feed them as for those that are intensively farmed. FoE Scotland further points out that the Soil Association’s organic standards for fish farms, introduced four years ago, are “interim”.

The Soil Association insists that organically farmed fish is reared to high standards, with the aim of producing disease- resistant stocks through good husbandry. “We try to use natural methods to keep the fish healthy,” says Sue Flook, for the association. “We have far lower stocking densities, with about half the number of fish in the same area as on conventional farms.” According to Soil Association rules, at least half of the feed ration for organic salmon must come from the by-products of wild fish caught for human consumption, with the balance provided by sustainable resources. Should you be seeking the MCS’s “responsibly farmed” salmon, then, the “organic” label is some assurance of this. Go for fish reared in large cages, at the confluence of the North Sea and the Atlantic. They have to swim, so are fitter and less fatty, while the fast-flowing tides flush away the effluent.

OTHER FISH TO FRY?

Trout and salmon are not, of course, the whole story. Other oily species supply plentiful omega-3 but these come with issues of their own. Handline-caught mackerel from the South West of England is judged sustainable but avoid it in the spawning season (January to April); herring stocks are off the danger list but some fishing methods involve the by-catch of marine mammals in the same way as dolphins fall victim to tuna fishing; and marlin and swordfish, for their part, are both endangered and have high levels of mercury.

SO, WHAT’S THE ANSWER?

Always do your homework and maybe embrace a different way of eating. Vegans will know that you can derive sufficient omega-3 from, for example, flax oil, walnuts, chestnuts, soya beans and tofu. If we all ate more of these, and fewer artery-clogging animal products, we would be healthier for it and, in the long run, so would our seas.

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