Fish oil, algal oil, krill and cod liver oil: which is which
Omega-3 capsules get their omega-3 from fish, krill, cod liver or algae. The source tells you whether a pack fits what you eat.
The oils side by side
| Omega-3 it carries | What sets it apart | |
|---|---|---|
| Fish oil | EPA and DHA | The amount in a capsule varies widely, so read the label |
| Algal oil | DHA, and in some EPA | A vegetarian source. Check the shell for gelatin. |
| Krill oil | EPA and DHA | Mostly in a form called phospholipids |
| Cod liver oil | EPA and DHA | Also gives vitamin A and vitamin D. If you are pregnant, ask your doctor first. |
| Flaxseed oil | ALA, the plant omega-3 | A food oil. The body turns only a small share into EPA and DHA. |
Fish oil
Fish oil carries EPA and DHA, which fish take in from algae in the sea's food chain.[1]
The NIH says a typical fish oil supplement gives about 1,000 mg of fish oil, with 180 mg EPA and 120 mg DHA. Amounts vary widely.[1]
Our article on omega-3 safety covers mercury and capsules.
Algal oil
ICMR-NIN, India's National Institute of Nutrition, first advises people who eat no fish to eat more plant omega-3 (ALA).[2] Its tables also list algal oil-based DHA products as a vegetarian source, and say to check the label for the amount.[2]
The NIH (US National Institutes of Health) says algal oil capsules usually give about 100 to 300 mg of DHA. In one small study, the body took up DHA from algal oil just as well as DHA from cooked salmon.[1]
To check for gelatin, read the ingredients on the back of the pack. Our article on how to read an omega-3 label explains the other lines on a pack.
Krill oil
The NIH reports that some studies found krill oil's phospholipids were taken up somewhat better than the omega-3s in fish oil. Others did not.[1]
Cod liver oil
Cod liver oil also gives vitamin A and vitamin D.[1] If you are pregnant, ask your doctor before you choose it.
Flaxseed oil, a food oil with ALA
Flaxseed oil, also called linseed oil or alsi oil, comes from a seed. The NIH fact sheet lists it with foods that give ALA, the plant omega-3, at 7.26 g in 1 tablespoon.[1] Flaxseed oil gives ALA, not EPA and DHA.
The body turns only a small share of ALA into EPA and DHA.[1] Our article on what omega-3 is explains why.
The form on the label
Some labels name the chemical form of the oil, such as triglyceride or ethyl ester. Here triglyceride means the oil's form, not the blood fat of the same name.
The NIH says triglyceride forms are absorbed somewhat better than ethyl esters, but every form raises the EPA and DHA in your blood.[1] A 2018 review says this ranking does not always hold in practice.[3] So read the milligrams of EPA and DHA first.
Our omega-3 guide covers how to choose a pack.
Ask your doctor before you take an omega-3 supplement if you take a blood thinner or any medicine regularly, are pregnant or breastfeeding, or are buying it for a child.
If you have a fish or shellfish allergy, ask your doctor before you take fish or krill oil.
Do not take more than the pack says.
Medical disclaimer: This article is general information. It does not replace advice from your doctor about your own health.
Common questions
Start with more plant omega-3 (ALA) from food, as ICMR-NIN advises. The body turns only a small share of ALA into EPA and DHA. Algal oils carry DHA, and some also carry EPA. Check the label for the amount, and check whether the shell lists gelatin.
ICMR-NIN names marine microalgae, the source of algal oil, as a vegetarian source of long-chain omega-3, the kind in fish. Read the ingredients to check what the capsule shell is made of.
The evidence is mixed. The NIH reports that some studies found krill oil's omega-3s were taken up somewhat better than those in fish oil, and others did not.
Sources
- National Institutes of Health, Office of Dietary Supplements. Omega-3 fatty acids: fact sheet for health professionals [Internet]. National Institutes of Health; 2025 Aug 22 [cited 2026 Oct 23]. Available from: ods.od.nih.govCited atIntroductionSources of omega-3s, Dietary supplementsSources of omega-3s, Dietary supplementsSources of omega-3s, Dietary supplementsSources of omega-3s, Dietary supplementsSources of omega-3s, Food, Table 2IntroductionSources of omega-3s, Dietary supplements
- ICMR-National Institute of Nutrition. Nutrient requirements for Indians: recommended dietary allowances and estimated average requirements, 2020. A report of the expert group. Hyderabad: ICMR-NIN; 2020. Updated 2024. Available from: nin.res.inCited atPrinted p. 115 (PDF p. 127)Table 6.6, printed p. 116 (PDF p. 128)
- Cholewski M, Tomczykowa M, Tomczyk M. A comprehensive review of chemistry, sources and bioavailability of omega-3 fatty acids. Nutrients. 2018;10(11):1662. doi:10.3390/nu10111662. PMID: 30400360. Available from: pmc.ncbi.nlm.nih.govCited atSection 3.2, Chemical binding