Farmed fish can be eaten as part of a balanced diet without any significant risk to human health from the trace levels of dioxins and related compounds present in the fish. These compounds are in the fish as a result of being present in the natural environment.

The main data available at present for aquaculture has been prepared for salmon. Dioxin levels measured in farmed salmon are lower, sometimes similar, to those in wild salmon from the same region.

Dioxins and other dioxin-like compounds occur naturally in the environment but their increased presence has been through man-made activities of. Typical levels found in food are so small they have to be measured as picograms (one millionth of a millionth of a gram, so 0,000000000001 gr) per kilogram of fish.

When the potential threat to the environment and human health from these compounds was recognised, steps were taken to eliminate or reduce them. Background levels began to fall in the 1980s and continue to do so. For example the US Environmental Protection Agency in its "Dioxin Reassessment Report" (June 2000) quotes a fall of 80% since monitoring began in the 1980s and the EU report, "Opinion of the Standing Committee on Food on the Risk Assessment of Dioxins and Dioxin-like PCBs in Food" (November 2000), noted that "the dietary exposure to dioxins in some European countries has decreased since the end of the 1980s by approximately 50%". This is encouraging since the ambient levels are much lower now than in the 1960s and 1970s.

In response to consumer concerns, the major feed-manufacturing companies have taken steps to further reduce dioxins in farmed fish by modifying their diets. A key concern is that any dietary changes should have a minimal impact on the levels of health-related omega-3 polyunsaturated fatty acids in the fish.

The specialist knowledge of the feed companies on the composition of fish oils will be applied to ensure these levels. There is substantial and growing evidence that omega-3 fatty acids have significant health benefits, ranging from established advantages for cardiovascular health and relief from pain in arthritis to emerging evidence of involvement in preventing cancers and a central role in mental health and brain function (see Nutrition section for details).

Eating salmon as part of a healthy balanced diet, as recommended by bodies such as the UK Food Standards Agency, means consuming an average of one portion of 130g per week. Given the trace levels of dioxins and PCBs found in the farmed salmon available in Europe, for a person weighing 70 kg this would represent around one-tenth of the tolerable intakes specified by the European Commission and the World Health Organization.

Further reductions of the dioxin content in feeds and hence the farmed fish can be obtained by using raw materials from areas of the world where the ambient background levels are lowest.

An additional possibility is the use of vegetable oils in combination with fish oils as an additional means of reducing levels of dioxins. Several major feed companies are participants in trials that are investigating the removal of dioxins from raw materials as well as the effects that such treatments have on the nutritional value of the feeds.