The Department of Health recommends eating two portions of fish, one of which should be an oily fish such as sardines, mackerel or salmon, each week. It's not much, but most of us don't manage to eat that amount - which means that many of us may be deficient in omega-3, the essential long chain fatty acids provided by oily fish. We are recommended to eat 3 grams of long chain omega-3 each week (0.45gram per day). That level of intake represents at least two portions of fish a week, including one portion of oily fish.