Fish Oil vs Algae Oil: EPA, DHA, Absorption and Who Each Suits

Quick Answer: Fish oil and algae (algal) oil both provide the long-chain omega-3s EPA and DHA. NIH’s Office of Dietary Supplements notes these omega-3s are originally made by microalgae and that algal-oil supplements usually provide about 100 to 300 mg DHA, some with EPA, while a typical 1,000 mg fish oil capsule provides about 180 mg EPA and 120 mg DHA. A small randomized study found algal-oil DHA bioequivalent to cooked salmon. Algae oil suits vegans and people avoiding fish. In the large VITAL trial, 1 g/day of fish-oil omega-3s did not lower major cardiovascular events overall, and a meta-analysis linked omega-3 supplements to higher atrial fibrillation risk.

Fish Oil vs Algae Oil at a Glance

Feature	Fish oil	Algae oil
Source	Fatty fish (anchovy, sardine, mackerel, etc.)	Cultivated microalgae
Typical omega-3 (ODS)	~180 mg EPA + 120 mg DHA per 1,000 mg capsule	~100–300 mg DHA; some add EPA
Example label (DSLD)	Nordic Naturals Ultimate Omega: 1,280 mg omega-3 per 2 softgels	Nordic Naturals Algae Omega: 715 mg omega-3 per 2 softgels
Vegan/vegetarian	No (and capsules often gelatin)	Yes (with plant-based capsules)
Mercury	Removed in processing (ODS)	Grown in controlled conditions
Fishy aftertaste	Common side effect	Less fishy for many people
Bioavailability evidence	Well studied	DHA equivalent to cooked salmon in one study

Doses above are from the current U.S. Drug Facts or prescribing labels listed in Sources. Always follow the label on the package you buy, because store brands and formulations differ.

Where Omega-3s Come From

The Office of Dietary Supplements explains that EPA and DHA are present in fish, fish oils and krill oils but are originally synthesized by microalgae at the base of the marine food chain; fish accumulate them by eating algae or smaller fish. Algal-oil supplements are made from microalgae grown in tanks, then extracted and purified. Plant oils such as flaxseed provide a different omega-3, ALA, which the body converts to EPA and DHA only in small amounts.

How Much EPA and DHA You Get

According to ODS, a typical fish oil supplement provides about 1,000 mg of fish oil containing 180 mg EPA and 120 mg DHA, though doses vary widely. Plant-based algal oil supplements usually provide around 100 to 300 mg DHA, and some contain EPA as well; they typically contain omega-3s in the triglyceride form. Concentrated products of either type can supply more.

Two labels in the NIH Dietary Supplement Label Database illustrate this. Nordic Naturals Ultimate Omega (fish oil) lists 1,280 mg total omega-3s per 2 softgels. Nordic Naturals Algae Omega lists 715 mg total omega-3s per 2 soft gels from marine algae oil. Always compare the EPA and DHA amounts per serving, not the total oil weight on the front of the bottle.

Is Algae Oil Absorbed as Well?

Arterburn and colleagues (Journal of the American Dietetic Association, 2008) randomized 32 healthy adults to 600 mg DHA per day from algal-oil capsules or from assayed portions of cooked salmon for 2 weeks. DHA levels rose by approximately 80% in plasma phospholipids and approximately 25% in red blood cells in both groups, and the authors concluded algal-oil capsules and salmon were bioequivalent sources of DHA. ODS cites this study. It was small and short and measured DHA only.

What Omega-3 Supplements Do and Do Not Do

The VITAL trial (Manson et al., NEJM, 2019) randomized 25,871 adults to 1 g/day of marine omega-3s (fish-oil derived) or placebo for a median 5.3 years. Major cardiovascular events (hazard ratio 0.92) and invasive cancer (1.03) were not significantly reduced overall. A secondary analysis suggested fewer heart attacks, but secondary findings need confirmation.

Gencer and colleagues (Circulation, 2021) pooled 7 trials with 81,210 participants and found marine omega-3 supplements were associated with a 25% higher risk of atrial fibrillation, with a larger hazard ratio in trials using more than 1 g/day. This applies to EPA and DHA regardless of source, and prescription high-dose omega-3s are a separate medical decision.

NCCIH summarizes that omega-3 supplements are not recommended in place of eating seafood and that the evidence for many claimed benefits is limited.

Safety

Common side effects of omega-3 supplements are mild: unpleasant taste, bad breath, heartburn, nausea and loose stools. Fish oil’s fishy burps are a common reason people try algae oil.
Bleeding: omega-3s may interact with anticoagulants such as warfarin; ask a clinician if you take a blood thinner.
Contaminants: ODS notes that omega-3 supplements have not been found to contain methyl mercury because it is removed during processing.
Fish allergy: people with fish or shellfish allergy should ask a clinician; algae oil avoids fish-derived ingredients.
Cod liver oil also contains vitamins A and D, which can add up with other supplements.

Choosing a Product

Check EPA and DHA per serving on the Supplement Facts panel.
Look for third-party testing seals such as USP Verified, or NSF Certified for Sport if you compete.
Check capsule material: fish-oil softgels usually use gelatin; vegan algae products use plant-based capsules.
Store away from heat and light to limit oxidation; a strongly rancid smell suggests the oil has degraded.

See also fish oil vs krill oil and our omega-3 benefits guide.

Putting It Together: Common Situations

The scenarios below summarize what the labels and guidelines cited on this page say. They are general information, not a personal treatment plan. Your pharmacist can check the choice against your other medicines, and your clinician can tailor it to your health history.

Vegan or avoiding fish: algal oil provides preformed DHA (and sometimes EPA), and its DHA was bioequivalent to cooked salmon in one study.
Wanting more omega-3 per capsule: compare EPA and DHA per serving; the DSLD examples on this page show the fish-oil product supplying more per serving.
Taking a blood thinner or with a heart rhythm history: talk to a clinician first; the Gencer meta-analysis linked omega-3 supplements to atrial fibrillation.

How to Read the Label Before You Buy

Find the active ingredient first. Brand names are often reused across products with different ingredients. The active ingredient and its strength appear at the top of the Drug Facts or Supplement Facts panel.
Check the “Uses” or labeled indication. A product is tested and labeled for specific uses. Using it for something else may not help.
Read the “Do not use” and “Ask a doctor before use” sections. They list conditions and medicines where the product may be unsafe.
Follow the directions for dose and duration. Note the maximum daily amount and how many days you can use it before checking with a clinician.
Check for duplicate ingredients. Combination products can contain the same ingredient as something else you take, which raises the risk of taking too much.
Note the “Stop use and ask a doctor” signs. These are the label’s own warning signs that a product is not working or is causing harm.

Common Mistakes to Avoid

Comparing total oil instead of EPA and DHA. The front label may show oil weight, not omega-3 content.
Expecting supplements to replace seafood. NCCIH notes the evidence for many claimed benefits is limited.
Assuming two products with similar names are interchangeable. Compare the active ingredients and strengths instead of the packaging.
Forgetting to tell your clinician. Keep a current list of every prescription, OTC medicine and supplement you take, and bring it to appointments and the pharmacy.

FormulaCompare does not recommend one brand over another. Use the sources below to check the details for the exact product in front of you, since formulas and labels can change.

When to Talk to Your Doctor or Pharmacist

Talk with a clinician before starting omega-3 supplements if you take a blood thinner, have a bleeding disorder or upcoming surgery, have atrial fibrillation or palpitations, have a fish or shellfish allergy, or are pregnant. Seek care for unusual bleeding or bruising, or a racing or irregular heartbeat.

Frequently Asked Questions

Is algae oil as good as fish oil?

A small randomized study found algal-oil DHA bioequivalent to cooked salmon. Algae oil often supplies less omega-3 per capsule, so compare EPA and DHA per serving.

Does algae oil contain EPA?

Some algae oils contain both EPA and DHA; many mainly provide DHA. Check the label.

Is algae oil better for vegans?

Yes. It provides preformed EPA and DHA without fish, and many products use plant-based capsules.

Does fish oil contain mercury?

The Office of Dietary Supplements notes omega-3 supplements have not been found to contain methyl mercury because it is removed during processing.

Do omega-3 supplements prevent heart attacks?

In the VITAL trial, 1 g/day did not significantly reduce major cardiovascular events overall. Talk to a clinician about your own risk.

Can omega-3 supplements cause atrial fibrillation?

A 2021 meta-analysis found a higher risk of atrial fibrillation with marine omega-3 supplements, especially above 1 g/day.

Sources

Medical disclaimer: This article is for educational purposes and does not replace medical advice. Consult a licensed healthcare provider before starting any supplement, medication, or treatment — particularly if you are pregnant, breastfeeding, taking other medications, or have a diagnosed medical condition.