The reason the Food Standards Agency have sought to limit our fish intake to one portion of oily fish a week is because research has shown that chemicals such as PCBs (polychlo-rinated biphenyls) and heavy metals are polluting our seas, and so contaminating the entire fish stock.
There is ongoing research to find out whether this is old pollution from a century of industrial emissions, or whether the current emissions are the main source of the pollution. The fish that arouse most concern are the larger fish, which have had longer to accumulate these toxins in their bodies. These include shark, swordfish and marlin, which have been found to be high in methylmercury levels. Shark is not considered an oily fish, but swordfish and marlin are. And although we in Britain do not eat a lot of these Pacific Ocean fish, increasingly we are seeing swordfish and shark in fishmongers, supermarkets and restaurants.
This sounds very alarming, but government health guidelines still recommend we eat the smaller oily fish such as salmon and mackerel once a week, and in fact a healthy adult is extremely unlikely to be affected by these contaminants unless they are consumed in vast quantities. Eating salmon, mackerel, trout or sardines once or twice a week is a good and healthy addition to your diet if you follow these guidelines:
- Pregnant women, women who want to become pregnant, babies and small children are advised not to eat shark, swordfish or marlin except occasionally, as high levels of these contaminants can interfere with the functioning of the nervous system.
- Stick to the other types of oily fish, such as the more common salmon and mackerel, which do not grow to such a large size, and have not been shown to be so affected.
- Know your fish. As it seems all fish stocks are contaminated with potentially dangerous pollutants, it is wise to know the source of the oily fish, and any other fish, you buy. A good fishmonger or supermarket will source their fish from areas of least pollution, so ask. Also avoid large, older fish of any type, whose flesh will be more likely to contain higher levels of contaminants. Fish farms have a more strictly controlled environment, so farmed salmon or trout should be less polluted.
