It's worth stopping to think about the true price of the salmon you eat. And there's quite a lot to think about.

Salmon is one of the biggest international seafood commodities, and in the UK it's easily one of the most consumed and most conspicuous species in our supermarkets and restaurants. But the vast majority of the salmon you'll find on shelves or plates these days has been farmed rather than fished. Partly that’s because there's hardly any wild Atlantic salmon left, but it's also because salmon's popularity has grown and it has gone from being a delicacy to become more of an everyday food in the past few decades.

50 per cent of fresh fish sold in supermarkets comes from farms

One obvious response to the disappearance of wild fish from our seas is "Why don’t we replace them with farmed varieties. We do it with land animals, so why not fish?" Of course this is already happening – over 40 per cent of the world's fish production already comes from aquaculture, and 50 per cent of fish sold in UK supermarkets comes from farms. These pen-reared fish grow at a phenomenal rate. For example, wild cod double in size every year, but hatchery cod quadruple in the same period. Given that size determines reproductive rate, at first glance this could be a solution to repopulating wild stocks.

Radioactive waste from Sellafield has been found in Scottish farmed salmon sold in major British supermarkets. Tests commissioned by Greenpeace revealed traces of radioactive waste in packets of fresh and smoked salmon.

Tc-99 is a byproduct of Magnox fuel reprocessing. Dr David Santillo, a scientist at Greenpeace's research laboratories at Exeter University, said: "Tc-99 should not be there at all. It is inexplicable yet significant. Scottish salmon is marketed as something that comes from a pristine environment."