Krill oil and fish oil are not the same thing, though they deliver the same core nutrients: the omega-3 fatty acids EPA and DHA. The differences lie in where those omega-3s come from, how they’re packaged at a molecular level, how well your body absorbs them, and what you’ll pay per capsule. For most people, the choice comes down to budget, tolerance, and how much omega-3 you actually need.
They Deliver Omega-3s in Different Molecular Forms
Fish oil comes from fatty fish like salmon, mackerel, and anchovies. The omega-3s in fish oil are stored as triglycerides, the same form your body uses to store fat. Krill oil comes from tiny shrimp-like crustaceans called Antarctic krill (Euphausia superba), and 30% to 65% of its omega-3s are bound to phospholipids instead. Phospholipids are the building blocks of cell membranes, which makes them structurally different from triglycerides in a way that matters for absorption.
The ratio of EPA to DHA also differs. Fish oil typically contains EPA and DHA in roughly equal amounts (about 1:1), while krill oil skews toward twice as much EPA as DHA (a 2:1 ratio). Both fatty acids are beneficial, but EPA is more closely linked to anti-inflammatory effects, while DHA plays a larger role in brain and eye health. If you’re specifically looking for high-dose DHA, fish oil gives you more of it per capsule.
Krill Oil May Be Absorbed More Efficiently
Because phospholipids are the same molecules that make up your intestinal cell walls, omega-3s bound to phospholipids may pass through the gut lining more easily. In a head-to-head bioavailability study, researchers gave healthy men identical 1,680 mg doses of EPA and DHA from either krill oil or fish oil and tracked blood levels over 72 hours. Krill oil produced the highest incorporation of EPA and DHA into blood plasma, roughly 34% more than the standard triglyceride form of fish oil and 68% more than the ethyl ester form (a cheaper, more processed type of fish oil).
One reason for this boost: krill oil naturally contains about 20% of its EPA and DHA as free fatty acids, which are absorbed without any additional digestion. Fish oil samples in the same study contained none. That said, better absorption from a single dose doesn’t automatically mean better long-term health outcomes. The clinical evidence for that is more nuanced.
Omega-3 Concentration Per Capsule
A standard 1,000 mg fish oil softgel typically delivers 300 to 500 mg of combined EPA and DHA, depending on the brand and concentration. Krill oil capsules are usually smaller (500 mg is common) and contain less total omega-3 per pill. In clinical trials, an average daily krill oil dose of about 1,875 mg provided roughly 385 mg of EPA and DHA. To get the same amount of omega-3 from krill oil as from a concentrated fish oil product, you generally need to take more capsules.
This matters if you need high-dose omega-3s for a specific purpose like lowering triglycerides. Prescription fish oil concentrates can deliver up to 4 grams of EPA and DHA daily, producing triglyceride reductions of 20% to 50%. Krill oil at typical supplement doses has shown only modest triglyceride reductions, around 6% to 10% compared to placebo. One study did find a 27% reduction at higher krill oil doses, but the overall body of evidence is far less robust than what exists for fish oil.
Effects on Cholesterol and Heart Health
One frequently cited trial found that krill oil lowered LDL (“bad”) cholesterol by 32% to 39% and raised HDL (“good”) cholesterol by 42% to 60%, dramatically outperforming fish oil. Those numbers sound impressive, but the study has been widely scrutinized for methodological issues, and later trials have not replicated such large effects. In more rigorous randomized controlled trials, krill oil produced small, often non-significant changes in cholesterol levels.
Fish oil, by contrast, has decades of large-scale cardiovascular research behind it. Its triglyceride-lowering effect at high doses is well established and forms the basis of FDA-approved prescription products. Fish oil does tend to cause a small bump in LDL cholesterol, something to be aware of if your LDL is already elevated. Krill oil’s effect on LDL appears more neutral, but the evidence base is thinner.
Krill Oil Contains a Built-In Antioxidant
Krill oil naturally contains astaxanthin, a red-orange pigment that gives krill (and flamingos) their color. Astaxanthin is a potent antioxidant, and its concentration in krill oil ranges widely from 40 to 5,000 mg per kilogram of oil depending on the product. This pigment helps protect the omega-3 fats in krill oil from oxidizing, which is why krill oil capsules tend to have a longer shelf life and are less prone to going rancid than fish oil. It also contributes to why krill oil capsules are typically red rather than the yellow-gold of fish oil.
Fish oil is more vulnerable to oxidation and can develop an off smell or taste over time, especially if stored improperly. High-quality fish oil products add vitamin E or other antioxidants to compensate, but krill oil has this protection built in.
Fishy Aftertaste and Digestive Comfort
One of the most common complaints about fish oil is the “fishy burp,” that unpleasant reflux taste that shows up an hour or two after swallowing a capsule. Krill oil users generally report fewer of these episodes. The phospholipid structure of krill oil disperses more readily in your stomach (think of how lecithin, another phospholipid, acts as an emulsifier in food). Triglyceride-based fish oil tends to float on top of stomach contents, which makes reflux more likely. The smaller capsule size of krill oil also helps if you find large softgels difficult to swallow.
Contaminant Levels and Food Chain Position
Krill sit near the very bottom of the ocean food chain, feeding on phytoplankton. Fish that are used for fish oil, even small species like anchovies and sardines, are higher up. Because heavy metals and pollutants like mercury and PCBs accumulate as you move up the food chain, krill are inherently lower in these contaminants. That said, reputable fish oil brands purify their products through molecular distillation, which removes most heavy metals and toxins. Both supplements, when purchased from quality manufacturers, typically test well below safety thresholds for contaminants.
Cost Difference
Krill oil costs significantly more than fish oil when you compare price per actual omega-3 content. Fish oil runs roughly 1 to 15 cents per 100 mg of EPA and DHA, while krill oil averages around 30 cents for the same amount. That means krill oil can cost two to thirty times more per milligram of omega-3, depending on which products you’re comparing. If you need high doses, say 2,000 mg or more of EPA and DHA daily, the cost gap becomes substantial over months of use.
Which One Makes More Sense for You
If your goal is high-dose omega-3 supplementation for triglyceride management, fish oil is the more practical and evidence-backed choice. It delivers more omega-3 per capsule, costs far less at therapeutic doses, and has a much larger body of clinical research supporting its cardiovascular effects.
Krill oil makes more sense if you’re taking a maintenance dose of omega-3s for general health, you’re sensitive to fishy aftertaste, or you prefer the potential absorption advantage of phospholipid-bound omega-3s. The built-in astaxanthin and lower contaminant risk are genuine perks, and many people find the smaller capsules easier to take consistently. Just know that you’re paying a premium for those benefits, and the clinical evidence supporting krill oil specifically is still catching up to what exists for fish oil.