Fish Oil vs Algae Oil: Sources, Forms and Who Might Choose Which

Omega-3 supplements come from fish, krill, fish livers and microalgae. The source changes which omega-3s you get, who can take it and what else is in the capsule. This guide compares them using NCCIH, the Linus Pauling Institute (LPI), the report behind the federal Dietary Guidelines and published research. It is general information for healthy adults, not medical advice. For the full set of buying checks, see our buying guide.

The sources, as NCCIH describes them

• Fish oil supplies EPA and DHA.
• Fish liver oil, such as cod liver oil, supplies EPA and DHA plus vitamins A and D in amounts that vary from product to product.
• Krill oil carries omega-3s in phospholipids.
• Algal oil is a vegetarian source of DHA, and some also contain EPA.

NCCIH adds flaxseed oil, which provides ALA rather than EPA or DHA. All of these are sold as dietary supplements, which FDA does not approve before they are marketed.

Why plant oils are not a stand-in

Flaxseed, chia, walnut and canola oils supply ALA. LPI summarizes studies in which about 8% of ALA became EPA and 0% to 4% became DHA in young men, and about 21% and 9% in young women, and it advises getting EPA and DHA from additional sources. The report behind the 2025-2030 Dietary Guidelines says ALA converts to EPA and DHA inefficiently, so vegans and vegetarians may not reach adequate long-chain omega-3 levels from food alone, and that an algal DHA and EPA supplement is an effective way to meet those needs. A 2022 scoping review of 13 trials, by Lane and colleagues, found that high-dose flaxseed or echium seed oil did not raise the omega-3 index, a measure of EPA plus DHA, and some studies showed reductions, while microalgal oil raised it in every study.

Algal oil: the vegan route to DHA

In a 2008 trial of 32 healthy adults, 600 mg of DHA a day from algal-oil capsules raised DHA in plasma phospholipids and red blood cells to a similar degree as DHA from cooked salmon over two weeks, and the authors called the capsules a safe and convenient source of DHA that does not come from fish. It was small and short, and we did not check who funded it, so treat it as one data point.

Check what the label lists. Some algal products supply DHA alone and others add EPA. LPI notes that the body can convert some DHA back to EPA, estimating about 7% to 14% depending on the measure in one study of omnivores and vegetarians, so DHA alone is not a dead end for EPA. A product that lists both lets you see the amounts. Algal oil with DHA and EPA on Amazon (opens in a new tab) is a search for these.

Fish oil and its forms

LPI notes that fish oil in its natural form is made of triglycerides, often with only one of the three fatty acids an omega-3, while ethyl esters are concentrated sources that supply more EPA and DHA per gram of oil. It also says that all omega-3 supplements are absorbed more efficiently with meals, and that splitting a day's dose into two or three smaller ones lowers the chance of stomach side effects. NCCIH lists the usual side effects as unpleasant taste, bad breath, bad-smelling sweat, headache, heartburn, nausea and diarrhea. Neither source tells you to prefer one form, so the practical test is the EPA and DHA per serving on the panel. Ethyl esters are also the form in the prescription products Lovaza and Vascepa, but those are drugs with set doses, and NCCIH says their effects may not match supplements. A search for fish oil in triglyceride form on Amazon (opens in a new tab) matches those words on a listing.

Krill oil

Krill oil carries its omega-3s in phospholipids, and LPI notes it is considered comparable to fish oil as a source of EPA and DHA. Krill are small crustaceans, and FDA lists crustacean shellfish among the nine major food allergens, so people with a shellfish allergy should ask their doctor before using it. Here is a search for krill oil softgels on Amazon (opens in a new tab).

Cod liver oil and vitamins A and D

NCCIH says cod liver oil contains vitamins A and D in amounts that vary by product and that both can be harmful in excessive amounts. LPI adds that some cod liver oil preparations may contain excessive amounts of preformed vitamin A and vitamin D. Look for the vitamin A and D lines on the Supplement Facts panel, and count them together with any multivitamin or other supplement you use. Our guide to vitamin D dose and upper limits explains the vitamin D side.

Fish and shellfish allergy, and what the label must say

FDA lists fish and crustacean shellfish among the nine major food allergens. It says the allergen-labeling law covers dietary supplements and requires the species of fish to be named, but excludes highly refined oils, so a missing "Contains" line is not a safe signal for a fish oil. The Lovaza and Vascepa labels say it is not known whether people with fish or shellfish allergies are at greater risk of a reaction, and advise caution. Our guide to the nine major allergens explains the law. If you have a fish or shellfish allergy, ask your doctor or an allergist before using any omega-3 product.

Vegan and vegetarian checks

Check the capsule shell as well as the oil. FDA's labeling guide requires ingredients not named in the Supplement Facts panel to appear under "Other Ingredients" in descending order by weight, and its own example list for a cod liver oil product reads "Cod liver oil, gelatin, water, and glycerin", which includes gelatin, an animal-derived ingredient. Read that line, and treat any vegan or vegetarian wording as the manufacturer's statement, since FDA does not approve supplement labeling before sale. A search for cod liver oil softgels on Amazon (opens in a new tab) shows how those labels read.

Choosing between them

The public sources we read do not name a winner. They do point to a few practical questions:

• Do you eat fish or avoid animal products? For avoiders, algal oil is the DHA route the federal report names.
• Do you have a fish or shellfish allergy? Ask a doctor first, whatever the source.
• Does the product list EPA and DHA per serving in milligrams, with a serving size you can follow?
• Does it contain vitamin A and D that add to other products you take?

Who should ask first

Talk to a doctor or pharmacist before you start if you are pregnant or breastfeeding, take blood-thinning medicine, have a fish or shellfish allergy or are buying for a child. NCCIH's tip sheet lists these groups, and the Lovaza label says omega-3 acids may prolong bleeding time. FDA advises everyone to check with a health care professional before using a supplement. The label on your pack is the authority on dose, ingredients and warnings.