The Food Standards Agency has issued advice on how much oily fish it is safe for people to eat.
Seven out of 10 people never eat oily fish, the FSA says
It says men, boys and women past childbearing age can eat up to four portions of oily fish such as salmon, tuna, trout and sardines a week.
Women of childbearing age should keep to a maximum of two portions a week.
Oily fish contains omega-3 fatty acids which help to prevent heart disease, but pollutants in the fish may also pose a health risk to human health.
The guidance suggests most people do not eat enough oily fish to gain a health benefit.
On average, people in the UK eat a third of a portion of oily fish a week. Seven out of 10 do not eat any at all.
However, experts are concerned about chemicals found in the fish such as dioxins and PCBs.
These can accumulate over time in the body and could have adverse health effects if consumed over long periods at high levels.
The levels of dioxins in oily fish vary and some types, such as herring, tend to have higher levels than others, such as trout.
The FSA experts based their recommendations on people eating different types of oily fish.
Sir John Krebs, FSA chair, said: "Eating oily fish is a simple way for people to reduce the risks of heart disease.
"Eating just one portion of oily fish a week has clear cut health benefits.
"This extensive review of the scientific evidence has reduced the uncertainty about how many oily fish people can safely eat without the benefits being outweighed by the risks."
The FSA expert group found that women should be most careful about their level of oily fish consumption because of the possible risks to the unborn baby.
However, they stressed that eating oily fish in moderation during pregnancy was a good idea because it helped the neurological development of the foetus.
Long standing public health advice continues to be that people should eat at least two portions of fish a week, and that one should be oily.
The agency already advises pregnant women, and women intending to become pregnant to avoid shark, marlin and swordfish and not to eat large amounts of tuna.
The guidance also stresses that occasionally eating more than the recommended amounts of oily fish will not be harmful.
Possible risks from chemicals such as dioxins are not immediate - they develop as the chemicals accumulate in the body over a long period of time.