Krill oil vs. fish oil vs. algae oil — The complete comparison

You're standing in front of a pharmacy shelf or scrolling through an online shop, and you see them all together: fish oil capsules, krill oil capsules, algae oil capsules. All promise optimal omega-3 supplementation, all contain EPA and DHA — yet they differ considerably in price, origin, bioavailability, sustainability and suitability. Which source is right for you? This article provides a science-based overview to help you make an informed decision — without marketing promises, but with concrete data and clear recommendations for different life situations.

Why the source of omega-3 fatty acids matters

Not all omega-3 supplement sources are equal. Although fish oil, krill oil and algae oil all provide EPA and DHA, they differ in one essential respect: the molecular form in which these fatty acids are present. This form influences how efficiently the body can absorb and utilise the fatty acids — what is known as bioavailability.

In nature, omega-3 fatty acids occur primarily as triglycerides (TG) — three fatty acid chains bound to a glycerol molecule. This natural form is found in fresh fish and in native fish oils. During processing into concentrated fish oil, a synthetic re-esterification is often carried out, yielding omega-3 fatty acids as ethyl esters (EE). Krill oil, in contrast, contains omega-3 fatty acids largely as phospholipids — a form that occurs naturally in cell membranes. Algae oil is generally present in triglyceride form.

Each of these forms has advantages and disadvantages that directly affect the efficacy, tolerability and price of the supplement. Sustainability, contaminant load and individual dietary habits also play an important role in choosing the right product. A more in-depth overview of all quality criteria can be found in the article What makes a good omega-3 oil?

Fish oil — The reference product with the broadest evidence base

Fish oil is by far the most intensively researched omega-3 supplement. The overwhelming majority of clinical studies demonstrating positive effects on cardiovascular health, blood lipids, inflammatory markers and cognitive function have been conducted with fish oil. For this reason alone, fish oil is the benchmark against which all other sources must be measured.

Production and composition

Fish oil is obtained from the body oil of fatty marine fish — primarily anchovies, mackerel, sardines and herring. These species sit at the lower end of the marine food chain, meaning they generally accumulate fewer heavy metals and other contaminants than larger predatory fish such as tuna or salmon. The crude oil is subsequently distilled, refined and in some cases concentrated to increase EPA and DHA content.

Typical fish oil capsules contain 300–600 mg EPA+DHA per capsule; high-concentration products can deliver up to 800 mg or more. The EPA:DHA ratio varies depending on the fish source and concentration level but frequently sits between 1.5:1 and 3:1 in favour of EPA.

Triglyceride form vs. ethyl ester form — an important distinction

When selecting a fish oil, the molecular form of the omega-3 fatty acids is critically important. Natural fish oil is present in triglyceride form (TG). The body absorbs this form well because the same digestive enzymes are used as for processing normal dietary fats.

Many budget fish oils on the market are, however, formulated as ethyl esters (EE). This synthetic form arises during the concentration of EPA and DHA and is cheaper to produce. Several bioavailability studies show, however, that triglyceride fish oil is absorbed better than ethyl ester fish oil — particularly when taken on an empty stomach. A study published in Prostaglandins, Leukotrienes and Essential Fatty Acids (PMID: 20638827) demonstrated up to 70 % higher bioavailability of TG oil compared to EE form under fasted conditions. A further advantage of TG form: it oxidises more slowly, improving shelf life and taste.

TOTOX value — the freshness indicator for fish oil

Omega-3 fatty acids are polyunsaturated fatty acids and therefore susceptible to oxidation. Oxidised fish oil smells strongly fishy, tastes rancid and in large amounts may even be counterproductive — some research groups debate whether highly oxidised fish oil can have pro-inflammatory effects.

The TOTOX value (Total Oxidation Value) is the most important quality indicator for fish oil. It is calculated from the peroxide value (PV, primary oxidation products) and the anisidine value (AV, secondary oxidation products): TOTOX = 2 × PV + AV. The Global Organization for EPA and DHA Omega-3s (GOED) recommends a TOTOX value below 26 for fish oil products. High-quality products often fall well below this, at 5–15.

A sign of good fish oil quality: the product is filled under nitrogen atmosphere, sold in opaque capsules or bottles, and has a short shelf life after opening. Refrigerating the oil after opening significantly extends its freshness.

Sustainability of fish oil

The ecological dimension should not be overlooked when purchasing fish oil. Since production consumes considerable quantities of fish — approximately 5–7 kg of wild fish are required to produce 1 kg of fish oil — the origin of raw materials is relevant. Certifications such as MSC (Marine Stewardship Council) or FOS (Friend of the Sea) confirm that the fish used comes from sustainably managed stocks. These labels are worth looking for when buying.

Common issues: fishy burps and taste

The biggest practical problem with fish oil is the "fish burp" — the fishy aftertaste many users find unpleasant. Enteric-coated capsules (gastro-resistant) can reduce this problem because the oil is only released in the small intestine. Alternatively, taking the capsules with food and storing them in the freezer can help.

Krill oil — Phospholipid-bound omega-3 with astaxanthin

Krill oil is derived from Antarctic krill — small shrimp-like crustaceans (Euphasia superba) that form the primary food of many marine mammals and seabirds in the Antarctic. Krill oil has received considerable marketing attention in recent years, often with promises of superior bioavailability and anti-ageing benefits from astaxanthin.

Phospholipid form: theoretical advantage, unclear evidence

The fundamental difference between krill oil and fish oil lies in the binding form of the omega-3 fatty acids: in krill oil, EPA and DHA are bound largely (typically 40–60 %) as phospholipids — that is, in the same form in which they occur naturally in cell membranes. The underlying theory: since the intestinal mucosa and cell membranes are themselves phospholipid-based, phospholipid-bound omega-3 fatty acids could potentially be absorbed more efficiently.

Some smaller studies do indeed show better absorption of omega-3 fatty acids from krill oil compared to ethyl ester fish oil. When krill oil is compared with high-quality triglyceride-form fish oil, however, the bioavailability advantage is much smaller or disappears entirely. A systematic review published in the journal Nutrients (PMID: 35274448) concludes that the evidence for a clearly superior bioavailability of krill oil compared to triglyceride-form fish oil is currently insufficient.

Astaxanthin — the natural antioxidant

Krill oil is the only one of the three omega-3 supplements that naturally contains astaxanthin — a carotenoid that gives krill its reddish-orange colour and is considered a potent antioxidant. Astaxanthin can slow the oxidation of omega-3 fatty acids in the oil and may itself have positive health effects. However, the amount of astaxanthin in krill oil capsules (0.1–0.5 mg per capsule) is modest compared to dedicated astaxanthin supplements.

EPA/DHA content per capsule — considerably lower than fish oil

A significant criticism of krill oil is the comparatively low EPA/DHA content per capsule. Whereas a typical fish oil supplement delivers 500–1,000 mg EPA+DHA per capsule, a krill oil capsule often contains only 90–250 mg EPA+DHA. This means that to reach the EFSA-recommended 250 mg EPA+DHA daily, two to four krill oil capsules are often required. For higher dosages (2,000–3,000 mg), krill oil is practically unsuitable due to its low active-ingredient content and high price.

Sustainability: Antarctic krill under pressure?

Antarctic krill plays a key role in the Antarctic ecosystem — as the primary food of whales, seals, penguins and many other animals. Krill stocks are currently considered large, but climate change and growing demand from the fish oil, krill oil and aquaculture industries are increasing pressure on these populations. Some environmental organisations have expressed concern. MSC certification for Antarctic krill and the CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) set catch quotas, but the sustainability debate is not yet closed.

Algae oil — The vegan source at the base of the food chain

Algae oil is, from a scientific and ecological perspective, the most interesting of the three omega-3 supplements. The idea behind it is compellingly simple: since fish and krill obtain their EPA and DHA from microalgae, why not go directly to the algae as the source? That is exactly what algae oil does.

Origin and production

Algae oil is derived from cultivated microalgae — primarily from the genera Schizochytrium, Crypthecodinium cohnii and Nannochloropsis. The algae are cultivated in controlled bioreactors under standardised conditions, without dependence on oceans or fish populations. This controlled production has several important advantages: no heavy metal contamination risk from marine pollutants, no seasonal variation in oil quality, and excellent traceability of ingredients.

DHA-rich, EPA variable — depending on the algae species

Most commercial algae oils are primarily rich in DHA — Crypthecodinium cohnii-based oils typically provide 200–400 mg DHA per capsule but very little EPA. Schizochytrium-based oils can provide both EPA and DHA in relevant amounts, as can Nannochloropsis-based products, which exhibit a higher EPA:DHA ratio. Newer algae oil products increasingly offer balanced EPA/DHA profiles and are therefore fully suitable as a fish oil alternative for all target groups.

Since many earlier algae oil supplements were primarily DHA-focused, they are particularly well suited for groups with a higher DHA requirement: vegans and vegetarians, pregnant and breastfeeding women, and people who specifically want to support brain and visual health.

Bioavailability: comparable to fish oil

Several controlled studies have directly compared the bioavailability of DHA from algae oil with that from fish oil — with encouraging results for algae oil. A study published in the Journal of the American Dietetic Association (PMID: 18589031) demonstrated a comparable increase in plasma DHA levels from both algae oil and salmon oil. Algae oil is generally present in triglyceride form, which explains its good bioavailability.

Sustainability and heavy metal safety

Algae oil scores on sustainability across the board: algae are produced in closed cultivation systems without any intervention in marine ecosystems. Since no marine organisms are involved, there is no risk of contamination with heavy metals such as mercury, lead or cadmium that accumulate in marine food chains. Algae oil is also vegan and therefore suitable for all dietary patterns.

Typical price: higher than fish oil, but justified

Algae oil is generally more expensive than fish oil and krill oil — primarily due to the more complex production process in bioreactors. For DHA-rich formulations with high-quality ingredients, prices of £0.45–1.35 per 250 mg DHA are typical. However, newer and more cost-efficient production methods are bringing prices down, so the gap compared to fish oil is steadily narrowing.

Direct comparison: krill oil vs. fish oil vs. algae oil

Feature	Fish oil	Krill oil	Algae oil
Typical EPA+DHA content per capsule	300–600 mg	90–250 mg	200–500 mg (predominantly DHA)
Molecular form	Triglyceride (TG) or ethyl ester (EE)	Phospholipid + triglyceride	Triglyceride
Bioavailability	High (TG) / Medium (EE)	Medium–high (controversial)	High (comparable to TG fish oil)
Sustainability	Medium (better with MSC/FOS certification)	Medium (CCAMLR quotas, debated)	Very high (bioreactors, no wild-fish extraction)
Suitable for vegans?	No	No	Yes
Heavy metal risk	Low (after distillation/refining)	Very low (short food chain)	No risk (not of marine origin)
Taste / fishy burps	Fishy (without enteric coating)	Slightly fishy / better tolerated	Neutral / no fishy taste
Typical price per 1,000 mg EPA+DHA	£0.18–0.55	£1.35–3.60	£0.72–1.80
Antioxidants in the oil	Added vitamin E where applicable	Astaxanthin (natural)	None (stable due to triglyceride form)
Research base	Very broad (hundreds of RCTs)	Limited (few direct comparative studies)	Growing (DHA bioavailability studies)

Which omega-3 supplement is right for you?

The answer depends on your individual circumstances. None of the three sources is inherently "better" — each has its strengths and weaknesses. The following recommendations help you make the right choice for your situation.

Fish oil: the best choice for most people

If you are not vegan or vegetarian, have no objection to animal products and are looking for good value for money, a high-quality fish oil in triglyceride form is the most sensible choice. Key things to look for: TOTOX value below 26, triglyceride form (rTG), MSC or FOS certification for sustainable sourcing, and a product filled under nitrogen atmosphere. With two to three capsules daily, a dose of 500–1,500 mg EPA+DHA can be achieved cost-effectively.

Krill oil: for people with specific preferences

Krill oil is a reasonable choice if you value the naturally contained antioxidant astaxanthin, prefer potentially better tolerability (fewer fishy burps), or find the phospholipid form appealing for specific reasons. However, you should be aware that you will need considerably more capsules and a much larger financial outlay than with fish oil to achieve the same EPA/DHA content. For high-dose omega-3 protocols, krill oil is practically unsuitable.

Algae oil: the first choice for vegans, pregnant women and those intolerant to fish oil

For vegans and vegetarians, algae oil has no alternative — it is the only plant-based source of directly usable DHA and (depending on the product) EPA. Pregnant and breastfeeding women also benefit from algae oil, as it provides highly pure DHA without heavy metal risk and optimally supports the baby's brain development. Anyone who dislikes the taste of fish or tolerates fish oil capsules poorly will also find algae oil a good alternative. More information on using algae oil in a vegan diet can be found in the article Omega-3 for vegans.

Quality criteria when buying — what to check for all three sources

Regardless of which omega-3 source you choose, there are universal quality criteria that should be checked for any product.

Certifications and transparency

High-quality omega-3 supplements are tested by independent laboratories for purity, contaminant content and active-ingredient levels. Look for IFOS certification (International Fish Oil Standards) for fish oil and krill oil — this confirms that the product meets maximum values for heavy metals, dioxins and PCBs, and has a low TOTOX value. For algae oil, equivalent certifications from independent laboratories verify purity and content. Manufacturers who publish their certificates transparently on their website or provide them on request are generally more trustworthy.

Storage and shelf life

Omega-3 fatty acids are sensitive to light, heat and oxygen. Fish oil capsules should be stored in the refrigerator after opening. Liquid fish oil keeps for approximately two to three months in the refrigerator after opening. Krill oil is somewhat more stable thanks to the astaxanthin it contains. Algae oil, in triglyceride form, is also more resistant to oxidation, but should likewise be stored in a cool, dark place.

Take with food

All three omega-3 sources are best absorbed when taken alongside a fat-containing meal. Dietary fats stimulate the secretion of bile acids and pancreatic lipase, which are necessary for the absorption of fats — and therefore omega-3 fatty acids too. Studies show that the bioavailability of EE-form fish oil when fasted is considerably lower than after eating; for TG form and algae oil the effect is less pronounced, but the basic principle applies to all three sources.

Frequently asked questions about krill oil, fish oil and algae oil