Oily fish are the richest food source of the long-chain omega-3 fats EPA and DHA. The fish most often named are salmon, mackerel, herring and sardines, with trout and pilchards also counted as oily by the NHS. White fish such as cod provide far less. This guide compares the main options, explains which ones count as “oily” in UK advice, and covers practical points such as portion sizes and mercury. It is general information, not individual advice.

How the fish compare

Figures for omega-3 vary with species, season, whether a fish is wild or farmed, and how it is prepared, so treat any table as approximate. The ranges below are for total omega-3 in a 3 ounce (85 gram) serving, as compiled in Wikipedia’s article on omega-3 fatty acids (Wikipedia).

Fish	Total omega-3 per 85 g
Herring and sardines	1.3 to 2 g
Salmon	1.1 to 1.9 g
Mackerel	1.1 to 1.7 g
Halibut	0.60 to 1.12 g
Tuna (fresh, varies by type)	0.21 to 1.1 g
Canned light tuna	0.17 to 0.24 g
Cod	0.15 to 0.24 g

For one specific example, the Harvard T.H. Chan School of Public Health’s Nutrition Source lists farmed Atlantic salmon as providing 733 mg of EPA and 935 mg of DHA in a 3 ounce raw portion, and wild Atlantic salmon 273 mg of EPA and 952 mg of DHA. It names salmon, mackerel, tuna, herring and sardines as high in EPA and DHA, and says fatty, dark-meat fish are the richest (Harvard Nutrition Source).

What counts as oily fish

The NHS defines oily fish as herring (including bloater, kipper and hilsa), pilchards, salmon, sardines, sprats, trout and mackerel. It says fresh and canned tuna do not count as oily fish for the purposes of its advice, which is why tuna sits in a lower position in many tables (NHS).

Tinned versions of sardines, pilchards, mackerel and salmon are still oily fish, although the canning liquid, bones and salt content vary. Smoked fish such as kippers also counts, though it tends to be saltier.

How much fish do health bodies suggest?

• NHS (UK). Adults are advised to eat at least two portions of fish a week, including one portion of oily fish. A portion is about 140 g. Girls and women who are planning a pregnancy, are pregnant or are breastfeeding, or who have not yet been through the menopause, should have no more than two portions of oily fish a week, because pollutants can build up and affect a baby’s development.
• FDA and EPA (US). For people who are or might become pregnant or are breastfeeding, the advice is two to three servings a week from the “Best Choices” list (or one serving from the “Good Choices” list), with a serving of 4 ounces. For children, it is two servings a week from the “Best Choices” list, with serving sizes that grow with age, from about 1 ounce at ages 1 to 3 to 4 ounces at age 11 (FDA).
• Harvard Nutrition Source. Eat fish or other seafood one to two times a week, which it says matters most for women who are pregnant or hoping to become pregnant, and for nursing mothers.

The exact advice differs by country, age and life stage, so check the national guidance where you live.

Mercury and choosing safer options

Fish can contain mercury and other contaminants. The FDA’s list of lower-mercury “Best Choices” includes anchovy, herring, salmon, sardines, freshwater trout, cod, shrimp and canned light tuna. Its “Good Choices” include albacore tuna and halibut. Its “Choices to Avoid”, with the highest mercury levels, include king mackerel, marlin, orange roughy, shark, swordfish, bigeye tuna and Gulf of Mexico tilefish. The NHS separately says that adults other than those who are pregnant or trying to conceive should have no more than one portion a week of shark, swordfish or marlin, and that children under 16, and anyone pregnant or trying to conceive, should avoid them. Mackerel is a case where the name matters: Atlantic and Pacific mackerel appear in tables as omega-3-rich, while king mackerel is on the FDA’s list to avoid.

Plant and other sources

Plant foods such as flaxseed, chia seeds, walnuts and rapeseed (canola) oil provide ALA, a shorter-chain omega-3. The Harvard source notes that the body converts ALA to EPA and DHA only to a limited extent, so ALA is an important omega-3 source mainly for people with fish allergies or vegan diets. Algal oil supplements offer a vegan source of DHA. The site’s article on healthy kitchen resets discusses pantry ideas, and the wellness articles index collects other general pieces.

Practical ways to eat more oily fish

1. Keep tinned sardines or mackerel in the cupboard for quick meals.
2. Grill, bake or steam instead of frying, which adds fat and calories.
3. Choose fish from sources that publish sustainability information.
4. Mix fresh and tinned fish through the week to keep costs reasonable.

Frequently asked questions

Which fish has the most omega-3?

By the ranges above, herring, sardines, salmon and mackerel are among the highest, but values vary by species, farming method and preparation.

Does tinned tuna count as oily fish?

Not in NHS advice. Fresh and canned tuna do not count, and canned light tuna is low in omega-3 compared with the oily fish listed above.

Is farmed salmon as good as wild?

Both provide EPA and DHA. The Harvard figures show different EPA and DHA totals for farmed and wild Atlantic salmon, so the profile differs.

Can I get the same from a supplement?

Supplements are discussed separately, and large trials have not shown that they provide the same protection as eating oily fish, according to the Harvard source. Ask a doctor or pharmacist before starting one.

This article is general information, not medical advice. A doctor or registered dietitian can advise on your own needs.