Health Benefits

Fish is highly nutritious. It is a good source of protein, vitamins B and E (A and D for the fatty species), minerals (such as calcium, phosphorus, iron, selenium, magnesium, fluoride and iodine) and essential fatty acids. Canned fish that retain their softened bones, such as salmon, sardines and pilchards also provide some calcium. Fish oils are rich sources of the fatty acids EPA and DHA (polyunsaturated fats), often referrred to as "omega-3" fatty acids. It is thought that these omega-3 fatty acids are cardioprotective and that consumption of fish (especially oily fish) can lower the risk of cardiovascular disease. These fats are also essential for normal brain development in unborn babies and infants. Fresh, frozen, canned and smoked versions of oil-rich fish provide EPA and DHA, except for canned tuna (as the oils are removed during processing). Protein levels between species are nearly always constant, but other flesh components (such as vitamin and fat content) differ greatly between species, due to physiological factors such as age and sexual maturity, as well as feed composition. Mineral and trace element content depends upon both water quality and dietary supply.

Possible sources of contamination

There are no consistent differences between wild and farmed fish in terms of food safety. In fact, given the controlled conditions under which aquaculture products are produced, farmed fish have the potential to be even safer than caught fish.

Fish species, season, location, diet, lifestage and age all have an important impact on both the nutrient and contaminant levels of fish. Dioxins and PCB's are environmental contaminants which may accumulate in the fatty tissues of fish. The dioxin content of oily fish varies between species (depending upon the relative fat content of the fish), but is very dependent upon the surrounding environment; herring has the potential to contain the greatest quantities, and trout the lowest, with salmon and mackerel having intermediate values. In terms of nutritional value, in general farmed fish have a higher fat content than wild-caught fish, which may have health benefits in terms of their contribution of unpolysaturated fatty acids, such as EPA and DHA, to the diet. Contaminants in fish derive predominantly from their diet, and levels of bioaccumulative contaminants are higher in fish that are higher in the food chain; therefore the levels of contaminants in farmed fish may be modified by altering their feed. Fish meal and fish oil are the most important sources of contamination of farmed fish feed with dioxin-like compounds. However, it should be kept in mind that there are other dietary sources of fat soluble contaminants, such as meat, therefore replacing fish with meat in the diet will not decrease dietary exposure to these contaminants.

Microbiological contamination may originate in the surrounding environment and be exacerbated by processing practices. However, control measures, including good hygiene practices and storage within a chilled environment at all stages in the processing chain, should ensure that proliferation is kept to a minimum.

If all medecines used for aquaculture treatment were licensed, and withdrawal periods were all strictly adhered to, there would be few, if any, residue problems. However, in reality there are many treatments on the market which are not licensed, or are used outside the terms of their licence, and withdrawal periods may be inappropriate. Control and monitoring methods vary significantly between countries, from almost non-existent to very strict. Within the EU there are strict laws concerning the control and monitoring of the use of medicines in aquaculture; outside of the EU a whole range of unlicensed medicines may potentially be used. A residue problem may arise due to the use of medicines not intially intended for a specific fish species, or due to individual country monitoring programmes not testing for all relevant residues. On the other hand, methods used for residue testing are increasingly sensitive, allowing detection of previously undetectable products. These issues (medicine licensing, use and surveillance) need to be addressed by standardisation on a worldwide basis.

See also: Consumer Protection & Product Quality