Fish Oil in dog and cat food

Is it OK for dogs and cats?

Dogs

At the levels used in complete foods, fish oil is a recognised source of EPA and DHA, and FEDIAF recommends some in foods for growing puppies. A veterinary review says possible side effects, such as diarrhoea, vomiting, weight gain and changes in platelet function, are likely to depend on the dose.

Cats

Fish oil is used in cat food too, and FEDIAF recommends small amounts of DHA/EPA for kittens because young cats make little DHA themselves. Cats need enough vitamin E alongside it. Pansteatitis has been reported in cats fed oily fish-based diets, and Merck links it to vitamin E deficiency. FEDIAF suggests extra vitamin E per gram of fish oil in cat food.

How settled this is: Depends on the amount

What fish oil is

Oil obtained from fish or parts of fish, with the water removed by centrifuging. The EU Catalogue of feed materials lists fish oil as a feed material and allows the name to include species details, so a label may name the fish (for example menhaden or herring); the EU's own example is cod liver oil. The EU lists hydrogenated fish oil, winterised fish oil (fish oil stearine) and krill oil as separate materials.

Why it is in pet food

To supply EPA and DHA, the long-chain omega-3 fatty acids. Merck names oily fish, krill oil and algae oil as the best dietary sources. During gestation and early life, DHA builds up in the brain and retina. FEDIAF reports better vision, measured by electroretinogram, in puppies whose mothers were fed long-chain omega-3s and that ate the same food after weaning. It recommends small amounts of EPA/DHA in foods for growth and reproduction. Vets also use fish-oil omega-3s to help manage several conditions in dogs and cats, many of them inflammatory. Merck says fatty acid supplements are often recommended for dogs with dry, flaky skin and dull coats, after underlying conditions have been checked. For essential fatty acid products in general, not fish oil alone, Merck reports that about 20% of dogs and 50% of cats with allergic itching show some improvement.

What it does in the food

Fish oil provides EPA and DHA. Plant omega-3 (alpha-linolenic acid, ALA, as in flaxseed oil) is not equivalent to EPA and DHA. Very young puppies can convert some ALA into DHA but lose this ability after weaning. Young cats have a low capacity to make DHA. FEDIAF recommends EPA + DHA of 0.05 g per 100 g dry matter in dog foods for growth and reproduction, and 0.01 g per 100 g dry matter in cat foods for growth and reproduction. For adult dogs and cats, it says the evidence is not yet enough to set a level. Like other oils, fish oil has about 9 kcal per gram.

Safety and limits

A 2013 veterinary review (Lenox and Bauer) listed possible adverse effects of omega-3 supplements in dogs and cats. These include changes in platelet function, diarrhoea and vomiting, slower wound healing, lipid peroxidation, nutrient excess and toxin exposure, weight gain, changes in immune function and glucose control, and drug interactions. The authors say effects, if seen, are likely to depend on the dose. Fish oil is especially unstable because EPA and DHA are highly unsaturated. Vitamin E helps protect against oxidation, and the vitamin E requirement rises as polyunsaturated fat intake rises. One study found lower blood vitamin E in dogs fed a fish-oil-enriched diet. FEDIAF notes that very high levels of long-chain omega-3s can reduce cellular immunity in dogs, especially when omega-6 intake is low. The review rates the overall risk from contaminants such as mercury as low. It notes that signs of mercury toxicity are seen more often in cats, because cats are fed fish-based diets more often. Merck notes that adverse effects of essential fatty acid supplements are few, that pancreatitis has rarely been reported, and that large doses may cause weight gain or diarrhoea.

What depends on the amount and the recipe

The total dose, including any supplement added on top of a complete food; vitamin E and other antioxidant protection; how fresh the oil is (oxidation); the balance of omega-6 to omega-3; species and life stage; and the pet's medical conditions and medicines, given possible effects on platelets and drug interactions.

Not the same as

• Salmon oil — Fish oil from one named species, salmon; it has its own page.
• Cod liver oil — A fish liver oil; reviewers flag possible vitamin A and D excess with high-dose supplements such as cod liver oil.
• Krill oil — Oil from marine plankton (krill), not fish; the EU catalogue lists it separately.
• Fish meal — A dried protein ingredient made from fish, not an oil.
• Flaxseed oil — A plant oil rich in ALA, which is not equivalent to EPA and DHA.

Sources

1. Commission Regulation (EU) No 68/2013 on the Catalogue of feed materials, consolidated text of 24.07.2022 (entries 10.4.2, 10.4.6–10.4.8 and 10.5.1) — Publications Office of the European Union, 2013 (consolidated 2022). Fish oil is oil from fish or fish parts, centrifuged to remove water, and its name may include species-specific details (e.g. cod liver oil); hydrogenated fish oil, fish oil stearine and krill oil are separate entries; fish meal is a separate heated, pressed and dried product.
2. FEDIAF Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs — FEDIAF (European Pet Food Industry Federation), 2025. EPA + DHA recommendations for growth and reproduction; no adult level set; DHA accumulates in brain and retina; improved vision in puppies from mothers fed long-chain omega-3s; puppies lose ALA-to-DHA conversion after weaning; young cats make little DHA; very high omega-3 can reduce cellular immunity in dogs; vitamin E needs rise with PUFA intake, with 5–10 IU extra per gram of fish oil per kg of cat food.
3. Lenox CE, Bauer JE. Potential adverse effects of omega-3 fatty acids in dogs and cats. J Vet Intern Med 27(2):217-226 — Journal of Veterinary Internal Medicine, 2013. Fish oil EPA/DHA used to manage several, often inflammatory, diseases; list of possible adverse effects; effects likely dose-dependent; fish oil especially unstable and vitamin E requirement rises with PUFA; lower plasma vitamin E in dogs fed fish oil; about 9 kcal per gram; low overall contaminant risk; mercury signs more common in cats; pansteatitis in cats on oily fish diets; ALA not equivalent to EPA/DHA; vitamin A/D concern with cod liver oil.
4. Nutritional Requirements of Small Animals (Merck Veterinary Manual, professional version) — Merck & Co. (Merck Veterinary Manual), 2024. Omega-3s (ALA, EPA, DHA) are required during growth and reproduction in dogs and cats; best sources of EPA and DHA are oily fish, krill oil and algae oil; best source of ALA is flaxseed oil; fatty acid supplements often recommended for dogs with dry, flaky skin and dull coats after checking underlying conditions; vitamin E deficiency causing pansteatitis in cats fed large amounts of canned tuna.
5. Essential Fatty Acids for Integumentary Disease in Animals (Merck Veterinary Manual) — Merck & Co. (Merck Veterinary Manual), 2022 (updated 2025). About 20% of dogs and 50% of cats with allergic itching improve on essential fatty acids; few adverse effects, pancreatitis rarely reported, and large doses may cause weight gain or diarrhoea.

Checked against these sources on 2026-10-15. Definitions are in our own words. This is a reading aid, not veterinary advice: a vet who knows your animal comes first.