Sourcing nutrition from the sea – fish, krill and algal omega-3

Pet parents want to know how food can elevate their pet’s health – and omega-3 fatty acids deliver a multitude of health benefits. Docosahexaenoic acid (DHA) is especially sought after for pet food due to its many and varied effects.

What is DHA?

DHA is one of the most important essential fatty acids. It is responsible for multiple positive effects, including soothing inflammation, supporting brain and eye health, and aiding skin and coat health. DHA can be derived from fish, krill and algal sources.

Weighing up sustainability

A diminishing supply of fish and its co-products amplifies the need for sustainable fishing practices, which are vital to protect the delicate balance of marine ecosystems.

This combined with increasingly volatile costs is leading formulators to search for alternative options to supply DHA omega-3, so they rely less on fish.

Krill is an alternative, but is similarly limited and therefore sensitive harvesting to ensure marine ecosystem balance is just as important. Algae has the potential to fulfil greater supply volumes.

Produced through fermentation or in photobioreactors, algae has been more costly yet provides greater sustainability advantages and supply stability.

Variations in yield

Yields of fish oil and component fatty acids are variable, and depend upon diet composition, which differs according to environmental factors. The quantity of fish required to yield a volume of fish oil varies with, and among, species, alongside age, sex and location, as well as with the season and reproductive stage.

The composition of fish oil fatty acids also varies dependent on these factors plus the environmental conditions of the fish, as well as the processing and stabilization of the oil. A 2016 study showed declining EPA and DHA fatty acids in farmed Scottish salmon oil over a 10-year period.

Reduction in fish meal and fish oils as a component of aquaculture feed, due to its increasingly limited supply and finite nature, is thought to be partly responsible. Terrestrial oils, such as those from oilseed crops, are included as a substitute, changing the fatty acid profile of fish produced.

Here, algal sources offer an advantage. With production through inoculum in photobioreactors or by heterotrophic fermentation, algae cultivation is consistent and unaffected by season, geographical origin or other environmental inputs.

Dangers of bioaccumulation

As DHA and eicosapentaenoic acid (EPA) bioaccumulate through predatory fish in the food chain, bioaccumulation of less desirable elements also occurs.

Heavy metal and other pollutants, such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT), increase in concentration up the food chain. Large fish species, like tuna, can therefore contain significant quantities of elements such as mercury.

This concern affects recommendations of fish inclusion within the diet, with some experts warning against daily consumption of fish. A 2015 article in the British Journal of Nutrition, however, advised that the benefits of fish consumption outweigh the risks.

As both krill and algae are found at the beginning of the food chain, the bioaccumulation of heavy metals and pollution is far reduced – although a 2025 study concerning the contamination of microplastics into omega-3 supplements found microplastics present in all marine formats, including algae.

Algae cultivated outside of the marine environment, however, is not affected by this pollution contamination.

Minimizing oxidation products

As polyunsaturated fatty acids, omega-3s are readily oxidized. In human nutrition, aldehydes were studied by nutritionists in New Zealand as a product of oxidation, with negative health effects from inflammatory to mutagenic properties.

This study, published in 2019, found the aldehydes present in krill oils to be greater than both fish and algal oils, with algal oils showing the least aldehyde content in this trial.

Oxidation is dependent on several factors, not least antioxidant inclusion and the storage and processing of the marine materials through the supply chain. Quality of marine DHA sources should be a key consideration for any supply, to minimize the oxidation products present in nutritional products.

Nutritional comparisons

The fatty acid profile of each omega-3 source varies, both between each source being investigated and between different species or supply. DHA supplied through fish sources varies from 3-38% depending on species alone. Salmon species have a variation of 3-18% DHA.

The DHA content of krill is approximately 6%, while for algae it is around 17%.

Although each source delivers DHA and EPA, the medium to which these fatty acids are bound differs. In fish, the omega-3 fatty acids are bound to triglycerides, whereas in krill omega-3 binds phospholipids.

The phospholipid form is claimed to be advantageous over triglycerides, as phospholipids are the lipid form of which the cell membrane is made. Triglycerides must be rebuilt into phospholipids prior to incorporation into the cell membrane and may be degraded or utilized as an energy source first.

Ensuring future supplies

Looking forwards, studies into DHA marine sources show concern regarding the finite nature of fish and the requirement for environmentally conscious practices and sustainable fishing.

DHA is an important nutrient delivering substantial and widespread benefits to health, therefore solutions to maintain its supply are a focus.

Key alternatives to marine oils being studied include bioengineered oilseed crops and the use of marine microbes to produce DHA.

Macroalgal hydrolysate in combination with glucose was recently found in a Japanese study to form an economical substrate for marine microbes to produce DHA in laboratory settings.

Stable multigene construct designs have previously been found to be successful in production of over 12% DHA in Camelina sativa oilseed crop. Both options show exciting possibilities for the future availability of DHA through sustainable terrestrial sources.

It is clear that the demand for DHA outweighs the supply of fish oil – even when only considering human nutrition. Understanding alternative sources is important to enable the continued use of omega-3 DHA within companion animal nutrition and to access its many health benefits.