Fish oil vs krill oil comes down to dose and price more than absorption. Both supply the same two omega-3s, EPA and DHA, and when trials matched the dose, blood levels and blood fats changed about the same with either. The big practical difference is on the label: the middle krill oil capsule in our label database holds about 100 mg of EPA and DHA, against about 520 mg for the middle fish oil capsule.
Below you'll find what the two have in common, how they differ, what the human studies found for heart, brain and joints, how to read an omega-3 label, and who should check with a doctor first. Our own grading covers fish oil across 270 human studies, with an improvement for blood pressure, blood fats, mood and joints; most krill oil trials are filed under fish oil and EPA and DHA in our grades, since they test the same omega-3s.
What Fish Oil and Krill Oil Have in Common
Both come from the sea and both are taken for EPA and DHA, the long-chain omega-3s your body makes only in small amounts. Fish oil is pressed from oily fish such as anchovies, sardines and mackerel. Krill oil comes from Antarctic krill, small shrimp-like animals near the bottom of the ocean food chain. Either one raises the omega-3 level in your blood within weeks.
Our omega-3 page and fish oil page list every human study we graded, the dose that worked and the products we rank.
Fish Oil vs Krill Oil: Key Differences
EPA and DHA per capsule. We read the omega-3 amounts on every capsule and softgel label in our label database: 270 krill oil labels and 504 fish oil labels. The middle krill oil label held about 103 mg of EPA plus DHA per capsule, and most fell between 88 mg and 155 mg. The middle fish oil label held about 522 mg, and most fell between 300 mg and 750 mg. To reach 500 mg of EPA and DHA a day, that is about five krill capsules or one fish oil capsule.
Absorption. In krill oil, most of the omega-3s are bound to phospholipids, the fats that make up cell walls; in fish oil, they are bound as triglycerides or ethyl esters. Krill oil is often sold as better absorbed. In 12 healthy men given the same 1,680 mg of EPA and DHA, krill oil raised blood levels the most over three days, but the differences were not significant (Schuchardt 2011). In 66 adults given the same 1.3 g a day for four weeks, blood and red-cell levels of EPA and DHA were about the same with krill oil and both kinds of fish oil (Yurko-Mauro 2015). In 113 adults over seven weeks, krill oil raised EPA and DHA as much as fish oil while giving about 63% of the dose, though the trial was not set up to prove krill oil absorbs better (Ulven 2011).
Astaxanthin. Krill oil carries astaxanthin, the red pigment that colors it. Labels list it in micrograms to a few milligrams per serving. It is an antioxidant, but we found no trial showing that the amount in krill oil changes a health outcome on its own.
Fish Oil vs Krill Oil: Side by Side
| Fish oil | Krill oil | |
|---|---|---|
| Source | Oily fish such as anchovies and sardines | Antarctic krill |
| EPA + DHA per capsule (middle label) | About 520 mg (most 300 mg to 750 mg) | About 100 mg (most 90 mg to 155 mg) |
| Capsules for 500 mg EPA + DHA | About 1 | About 5 |
| Form of the omega-3s | Triglycerides or ethyl esters | Mostly phospholipids |
| Absorption at the same dose | About the same in matched trials | About the same in matched trials |
| Blood fats, dose for dose | No difference in 64 pooled trials | No difference in 64 pooled trials |
| Cost per gram of EPA + DHA | Usually lower, since each capsule holds more | Usually higher, unless the capsules cost a fifth as much |
| Purity | Look for third-party testing for oxidation and contaminants | Same; krill is low on the food chain |
| Sustainability | Look for a fishery certification on the label | Look for a fishery certification on the label |
| Our grading | Improvement for blood pressure, blood fats, mood and joints (270 human studies) | Graded with fish oil and EPA and DHA |
Not sure which fits you? Get a protocol that picks for you.
What the Research Shows for Heart, Brain and Joints
Blood fats. A network analysis of 64 trials found that each gram of omega-3s lowered triglycerides by about 9 mg/dL with fish oil and about 10 mg/dL with krill oil, and the two did not differ on triglycerides, LDL, HDL or total cholesterol. What mattered was the dose of omega-3s, not the source (Kim 2020). Our cholesterol goal page ranks the ingredients for blood fats.
Blood pressure. Across 31 placebo-controlled trials of 1,356 people, fish oil lowered blood pressure by about 3.0/1.5 mm Hg on average, with larger effects at higher doses and in people with high readings (Morris 1993). Our grade for fish oil and blood pressure is an improvement; see our blood pressure goal page. We found no blood pressure trial of krill oil large enough to compare.
Heart events. In 25,871 US adults over 50 followed for about five years, 1 g a day of fish oil omega-3s did not lower the combined rate of major heart and blood vessel events against placebo, and caused no excess bleeding (Manson 2019). There is no trial of krill oil of that size.
Joints. Krill oil has two placebo-controlled joint trials. In 235 adults aged 40 to 65 with wear-and-tear knee pain, 4 g of krill oil a day for six months improved knee pain, stiffness and function modestly more than placebo (Stonehouse 2022). In 50 adults with mild knee pain, 2 g a day for 30 days eased pain and improved range of motion (Suzuki 2016). For fish oil, a review of 42 trials found marine oils modestly reduced joint pain overall, but not in the five trials of wear-and-tear joint problems, and most of the evidence was low quality (Senftleber 2017). Our joints and mobility goal page has the full ranking.
Muscle. In 102 healthy adults over 65, 4 g of krill oil a day for six months increased muscle strength and size against placebo (Alkhedhairi 2022).
Eyes. In 60 adults with dry, irritated eyes, fish oil and krill oil both improved tear stability over 90 days, and only krill oil improved symptom scores (Deinema 2017). Across 56 human studies, our grade for fish oil and eye health is no clear effect.
Brain and mood. Our grade for fish oil and mood is an improvement across 53 human studies; we found no large trial comparing krill oil with fish oil for memory or focus.
How to Read an Omega-3 Label
The big number on the front, such as "1,000 mg fish oil" or "500 mg krill oil", is the weight of the oil, not the omega-3s. Turn to the Supplement Facts panel and add EPA and DHA, then check the serving size: many labels list two or more capsules per serving.
To compare cost, divide the bottle's price by the total grams of EPA and DHA in it (EPA plus DHA per serving, times servings per bottle). This is where krill oil usually loses ground, since each capsule holds about a fifth as much.
Labels are not always right. When every fish oil sold in New Zealand was tested, only 3 of 32 held the EPA and DHA on the label, and most had oxidation levels above recommended limits (Albert 2015). A larger database of more than 1,900 fish oil samples tested by a third party found most met oxidation limits (De Boer 2018). A third-party seal and a fresh, non-fishy smell are good signs. You can look up any omega-3 label in our supplement label database.
Check Against Your Meds
Omega-3s can add to the effect of meds that thin the blood or lower blood pressure, so check with your doctor or pharmacist before starting, especially at high doses. Krill oil comes from a shellfish, so skip it if you are allergic to shellfish. The most common side effects of either are fishy burps, an upset stomach and loose stools. Rala, the AI behind Reverse Age Lab, checks every product in your stack against your meds before it places anything in your protocol, and blood work is optional.
Is this medical advice? No. This guide sets out the published research on fish oil and krill oil; it is not a diagnosis, and Rala isn't a medical device or a clinician. Talk to your doctor before adding either, especially if you take meds, are pregnant or have a shellfish allergy.
Bottom Line: Which One Gives Better Value?
Dose for dose, the studies found no clear difference between fish oil and krill oil for absorption or blood fats. Krill oil adds astaxanthin and has its own joint and muscle trials, but each capsule holds about a fifth of the EPA and DHA, so reaching a given dose usually takes more capsules and costs more. Fish oil has far more trials behind it. Either way, the number that matters is the EPA and DHA you get each day.
Check Your Omega-3 Dose Against Your Whole Stack
Your Daily Protocol adds up the EPA and DHA in every product you take, including multivitamins and blends, checks it against your meds, and places each one at the right time of day. Build My Protocol – 7-Day Free Trial.
Frequently Asked Questions
Fish oil vs krill oil: which is better?
Neither came out ahead in the trials that matched the dose: blood levels of EPA and DHA and blood fats changed about the same. Fish oil gives more EPA and DHA per capsule and has far more trials; krill oil adds astaxanthin and has a few joint and muscle trials of its own.
Fish oil vs krill oil for cholesterol: which lowers it more?
Across 64 trials, they did not differ on triglycerides, LDL, HDL or total cholesterol. Each gram of omega-3s lowered triglycerides by about 9 to 10 mg/dL with either source.
Is krill oil absorbed better than fish oil?
One small study of 12 men found a trend toward higher levels with krill oil, but a four-week trial of 66 adults given the same dose found about the same blood levels with both.
What about cod liver oil, algae oil and salmon oil?
Cod liver oil also carries vitamins A and D, which count toward their upper limits. Algae oil is the plant-based source of EPA and DHA. Salmon oil is a fish oil. For any of them, compare the EPA and DHA per serving.
How much EPA and DHA should I take?
The trials in this guide gave from about 0.5 g to 4 g of EPA and DHA a day, and the effect on blood fats grew with the dose. The European Food Safety Authority found up to 5 g a day of EPA and DHA combined raises no safety concern for adults. Check higher doses against your meds first.
Sources
Schuchardt JP, Schneider I, Meyer H et al. Incorporation of EPA and DHA into plasma phospholipids in response to different omega-3 fatty acid formulations: a comparative bioavailability study of fish oil vs. krill oil. Lipids in Health and Disease, 2011. PubMed.
Yurko-Mauro K, Kralovec J, Bailey-Hall E et al. Similar eicosapentaenoic acid and docosahexaenoic acid plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study. Lipids in Health and Disease, 2015. PubMed.
Ulven SM, Kirkhus B, Lamglait A et al. Metabolic effects of krill oil are essentially similar to those of fish oil but at lower dose of EPA and DHA, in healthy volunteers. Lipids, 2011. PubMed.
Kim MG, Yang I, Lee HS et al. Lipid-modifying effects of krill oil vs fish oil: a network meta-analysis. Nutrition Reviews, 2020. PubMed.
Morris MC, Sacks F, Rosner B. Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation, 1993. PubMed.
Manson JE, Cook NR, Lee IM et al. Marine n-3 fatty acids and the prevention of major heart and blood vessel events (VITAL trial). New England Journal of Medicine, 2019. PubMed.
Stonehouse W, Benassi-Evans B, Bednarz J et al. Krill oil improved knee pain in adults with mild to moderate wear-and-tear knee problems: a 6-month multicenter, randomized, double-blind, placebo-controlled trial. American Journal of Clinical Nutrition, 2022. PubMed.
Suzuki Y, Fukushima M, Sakuraba K et al. Krill oil improves mild knee joint pain: a randomized control trial. PLoS One, 2016. PubMed.
Senftleber NK, Nielsen SM, Andersen JR et al. Marine oil supplements for joint pain: a systematic review and meta-analysis of randomized trials. Nutrients, 2017. PubMed.
Alkhedhairi SA, Aba Alkhayl FF, Ismail AD et al. The effect of krill oil supplementation on skeletal muscle function and size in older adults: a randomised controlled trial. Clinical Nutrition, 2022. PubMed.
Deinema LA, Vingrys AJ, Wong CY et al. A randomized, double-masked, placebo-controlled clinical trial of two forms of omega-3 supplements for dry, irritated eyes. Ophthalmology, 2017. PubMed.
Albert BB, Derraik JG, Cameron-Smith D et al. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Scientific Reports, 2015. PubMed.
De Boer AA, Ismail A, Marshall K et al. Examination of marine and vegetable oil oxidation data from a multi-year, third-party database. Food Chemistry, 2018. PubMed.
