algae oil vs fish oil: which omega-3 is better?

Algae oil and fish oil give you the same two omega-3s, EPA and DHA, and the trials that have compared them head to head found the same amount arriving in the blood. The differences are further back: where the oil starts, how far it travels, and what it picks up along the way.

what is algae oil?

Algae oil is omega-3 taken from a specific type of micro-algae found in coastal environments around the world. This algae is grown in closed tanks rather than harvested from the sea.

This algae is the original source of marine omega-3. Fish don't make EPA and DHA. They accumulate it, by eating algae or by eating something that ate algae, such as plankton or krill. [1] Taking it from algae skips the fish and goes to the original producer.

what is fish oil?

Fish oil is pressed from oily fish, and mostly from one fish in one place. Most of the world's fish oil comes from Peruvian anchoveta. Annual catches run to more than 4 million tonnes, of which roughly 38,000 tonnes of anchovy oil is extracted for supplements. [11]

does algae oil work as well as fish oil?

Yes. Measured by how much omega-3 reaches your blood, they come out the same.

A randomised trial gave 32 adults either algae oil capsules or portions of cooked salmon, both at 600 mg of DHA a day for two weeks. DHA rose by around 80% in plasma phospholipids and around 25% in red blood cells, and the change was similar in both groups. The researchers concluded the two were bioequivalent. [2]

A larger double-blind trial published in 2025 followed 74 adults for 14 weeks on either microalgal or fish oil, and measured both EPA and DHA. Microalgal oil came out statistically non-inferior to fish oil for both. [3]

does fish oil contain contaminants?

Usually some, and this is why the source and the quality of the manufacturing start to matter.

Industrial pollutants like PCBs, dioxins, heavy metals and flame retardants don't break down easily. They wash into the ocean, and because they dissolve into fat rather than water they concentrate as they move up the food chain, ending up inside the bodies of fish. 

Surveys keep finding traces. A Canadian study of 30 supplements found detectable flame retardants in every single sample. [9] A UK survey of 33 products found 12 of them would have breached the EU dioxin limit that was introduced shortly afterwards. [6] A Czech analysis of 44 supplements found PCBs, pesticides, flame retardants and PAHs across a wide range, and noticed something else: four products sold as fish oil appeared to be cheaper cod liver oil, and those carried more pollutants than the rest. [7]

It would be easy to stop there. Testing of 37 products on the Japanese market in 2024 found PCB intakes well below the tolerable daily intake set by the WHO, and concluded the risk was acceptable. [8] Dioxin levels in fish oil have fallen over the past two decades. [6]

This doesn't necessarily mean that all fish oil is dangerous. It is usually put through a distillation process to remove these contaminants, and some countries have regulation in place to ensure the toxins don't exceed a certain limit. However, that doesn't mean they're removed completely.

On the other hand, algae is grown in a closed tank in purified water, so it never encounters contaminants in the first place, so there's nothing to remove.

do omega-3 supplements go rancid?

Yes. Omega-3 fats are fragile, regardless of the source. Heat, light and air break them down, and once an oil has oxidised you can't restore it. The industry's own voluntary quality threshold is a total oxidation value of 26, and products are tested against it.

A 2024 analysis of 72 supplements covering algae, fish, krill, calamari and mussels found the strongest single factor wasn't the source at all. It was flavouring. Among flavoured products, 68% exceeded the oxidation limit. Among unflavoured ones, 13% did. [4]

Flavouring is added to cover the taste of fish oil, and it covers the taste of oxidised oil just as well. Smell isn't a reliable guide either way. [11]

Algae oil isn't exempt from oxidation, but the process makes it far less likely to happen during manufacture. It doesn't have to travel very far and is kept in controlled conditions. 

Fish oil is a different story. Most of it is caught off Peru, sent to China for extraction and distillation, then shipped back to Europe or North America for packaging, and it needs to be kept cold and handled quickly at every one of those steps [11]. This significantly increases the risk of oxidation. 

is fish oil sustainable?

Mostly, no.

The FAO tracks how many of the world's assessed marine fish stocks are being fished within biologically sustainable levels. In 1974 that was 90%. By 2021 it was 62.3%, down another 2.3 points from 2019, while the share fished unsustainably climbed from 10% to 37.7% over the same period. [17]

Around a tenth of the world's farmed and caught aquatic animals never reaches a plate at all. It goes to non-food uses, mostly fishmeal and fish oil. [17]. Furthermore, fish oil is usually extracted from smaller fish such as sardines or anchovies, which remove a food source for larger creatures further up the food chain. 

Stock numbers aren't the only cost. Bycatch, the accidental capture of animals nobody was fishing for, is described by the International Whaling Commission as by far the single most serious threat to whales and dolphins, and it estimates at least 300,000 of them are killed in fishing gear every year. [18] WWF puts the wider annual toll at roughly 720,000 seabirds, 345,000 seals and sea lions, over 250,000 turtles and more than 1.1 million tonnes of sharks and rays. [19]

This doesn't even factor in the 600,000 to 1M tonnes of discarded fishing gear that enter the oceans every year. 

Growing omega-3 in a tank from micro-algae doesn't require fishing gear in the water at all, making it far more sustainable.

will there keep being enough fish oil?

These figures come from the fish oil industry's own trade body, not from us.

Peru accounts for around 20% of world fishmeal production. [10] Its 2026 anchovy quota was set at 1.9 million tonnes, about 27% of the estimated remaining population. Fishing was interrupted repeatedly, then suspended on 10 June with only about a quarter of that quota caught. As of late August, El Niño conditions were forecast to last into early 2027 and fishing in the main zone remained, in IFFO's words, effectively inactive. [10]

That isn't a one-off. The second season of 2014 was cancelled outright, and in 2016 the first season was called off early with less than half the quota met, taking world fish oil production down 35% over six months. [16]

Algae doesn't depend on any of that. It's grown to order in tanks, so the supply isn't a function of ocean temperature or of how many anchovy are left.

how does flaxseed compare?

Flaxseed comes up a lot as the plant alternative, and it's a different thing entirely.

Flaxseed, chia and walnuts give you ALA, the short-chain plant omega-3. Your body converts some of that to EPA, at around 6% on an ordinary diet. [12] Conversion onward to DHA is very low to negligible: the range runs from about 4% at the generous end down to nothing, and when people simply eat more ALA for weeks or months, reviews find no reliable rise in blood DHA. [13][14]

So flaxseed is a good food, but a poor source of EPA and DHA, which is where the benefits are. It isn't really comparable to fish or algae oil, because it doesn't give you EPA and DHA in the first place.

should you take algae oil or fish oil?

If you eat oily fish twice a week, which is what the NHS recommends, you should already be getting EPA and DHA and you don't need either. However, most people in the UK don't manage it. [15]

If you're taking a supplement, both work. What separates them is upstream: algae starts clean and is made in one place, fish oil starts in an ocean carrying two centuries of industrial pollution and travels a long way before it reaches you. Plus it contributes to the damage being done to the oceans by industrial fishing.

Ours is vegan omega-3 DHA and EPA from algae.

Whichever you choose, buy it unflavoured. Read the milligrams of EPA and DHA per serving rather than a combined "total omega-3" figure. And check the date, because freshness is the one quality marker you can actually see.

the bottom line

Algae oil and fish oil deliver the same nutrients, and the head-to-head trials found no meaningful difference in what reaches your blood.

Everything that separates them happens before the capsule. Fish oil accumulates contaminants from the ocean, and while distillation and regulation can keep them low, they don't remove them. It travels from Peru to China to Europe, and omega-3 oil doesn't travel well. And it comes out of a system where the share of stocks fished sustainably has been falling for decades.

Oxidation is the one problem both share. So buy unflavoured, check the date, and make sure it's kept in a cool, dry place away from sunlight.