Krill oil and fish oil both supply the omega-3 fatty acids EPA and DHA, but they come from different animals and package those fats differently. Fish oil is pressed from oily fish and carries omega-3 mostly as triglycerides. Krill oil comes from small Antarctic crustaceans and holds a portion of its omega-3 in phospholipids. Whether that difference gives krill oil a real advantage is still debated.

Where each one comes from

Fish oil is made from oily fish such as anchovy, sardine, mackerel and herring, or from fish liver in the case of cod liver oil (which also contains vitamins A and D). Some products are concentrated to raise the EPA and DHA content.

Krill oil is extracted from Antarctic krill, Euphausia superba, small shrimp-like crustaceans that feed on microalgae. The fishery in the Southern Ocean is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), an international body. The site’s pages on Antarctic krill and krill oil describe the animal in more detail.

How the omega-3 is packaged

Fats in supplements appear in different molecular forms.

Feature	Fish oil	Krill oil
Animal source	Oily fish	Antarctic krill
Main omega-3 form	Triglycerides, or ethyl esters in concentrates	Part phospholipid, part triglyceride and free fatty acid
Typical EPA and DHA per capsule	Often higher	Often lower
Other natural compounds	Vitamins A and D in liver oils	Astaxanthin, a red carotenoid pigment, in small amounts; choline from phospholipids
Shellfish allergy relevance	Fish allergy relevant	Krill are crustaceans, so shellfish allergy is relevant
Capsule size	Varies, often larger	Often smaller

The absorption question

Some small studies have suggested that omega-3 bound to phospholipids is taken up into blood more readily than omega-3 in some other forms, which is the main argument for krill oil. Other studies found little difference once doses were matched, and the research is limited by small sample sizes, short durations and different products and doses. The US National Institutes of Health notes that evidence on differences between forms is still emerging. A fair summary: krill oil may be absorbed well at lower doses, but “better” has not been established for health outcomes.

What about astaxanthin?

Astaxanthin is the pigment that gives krill oil its red color. It is also an antioxidant in laboratory settings. The quantity in a typical capsule is small, and claims about health effects at those amounts are not established. Its presence also means krill oil may look and taste different from fish oil.

Sustainability and sourcing

Both krill and fish are wild-caught, and both raise sustainability questions. Fish oil sourcing depends on the species and fishery, while krill is regulated through catch limits set by CCAMLR. Certification schemes, such as those run by the Marine Stewardship Council, are one way to check how a fishery is managed. Quotas, biomass estimates and bycatch rules are the main points to look at when comparing fisheries.

A simple comparison scenario

Imagine two generic products. One fish oil capsule lists 300 mg of EPA plus DHA; one krill oil capsule lists 100 mg. A reader comparing only the number of capsules might think they are equal, yet the fish oil capsule carries three times as much of the two fatty acids. If krill oil were absorbed three times better, the totals would match, but studies have not shown a gap that large. The point is not that one product wins. It is that the label amounts, the serving size and the price per serving of EPA and DHA need to be compared before any claim about form is considered. The numbers here are invented for illustration and do not describe a real product.

Safety and who should ask first

Omega-3 supplements are generally well tolerated, with fishy aftertaste, burping or stomach upset the usual complaints. But some people should speak to a healthcare professional before using either:

• Anyone taking anticoagulant or antiplatelet medicines
• People with shellfish or fish allergies
• Pregnant or breastfeeding women
• People scheduled for surgery
• Anyone with a chronic condition or taking regular medicines

How to compare products

1. Read the amount of EPA and DHA per serving, not just “total oil” on the front.
2. Check the serving size, which may be several capsules.
3. Look for third-party testing for contaminants and oxidation.
4. Check storage instructions. Omega-3 oils can go rancid.
5. Note the source species and, for krill, any sustainability certification.

The guide to reading a krill oil softgel label walks through typical label entries.

Frequently asked questions

Is krill oil better than fish oil?

Not proven. Krill oil has a different structure and may be absorbed well, but fish oil often provides more EPA and DHA per capsule. Neither has been shown to be superior for health outcomes.

Can I take krill oil if I’m allergic to fish?

Krill are not fish, but cross-contamination and individual allergies vary. Ask an allergist.

Does krill oil have less fishy aftertaste?

Many users report this, but experiences differ.

Do I need a supplement at all?

Many health agencies recommend eating oily fish as the first source. Supplements are an option to discuss with a professional.

Takeaway

The main differences are source, structure and concentration, not a clear difference in proven benefit. For personal decisions, including dose and safety, speak to a doctor, pharmacist or registered dietitian. The NIH Office of Dietary Supplements has an omega-3 fact sheet with reviewed evidence.