Fish oil might be the most universally useful supplement you can add to a dog's diet. Unlike glucosamine or chondroitin — where the evidence is genuinely mixed — the research on omega-3 fatty acids for dogs is consistent, broad, and backed by organisations including the American Kennel Club and the American Animal Hospital Association.
Here's what it actually does, what to look for, and when to give it.
What Fish Oil Contains — and Why It Matters
Fish oil is rich in EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — long-chain omega-3 fatty acids that dogs cannot produce themselves and must consume through diet.1 Unlike plant-based omega-3s (such as flaxseed oil), fish oil provides EPA and DHA directly — dogs have very limited ability to convert the plant-based ALA precursor into the forms their body can use.2
What Fish Oil Does for Your Dog
Joint health
EPA and DHA target inflammation directly via the COX and LOX inflammatory pathways — the same pathways that prescription NSAIDs act on, though less potently. The American Animal Hospital Association recommends omega-3s as a first-tier option for joint support in dogs.3 It takes approximately 2 months for omega-3s to fully incorporate into cell membranes, so don't expect results in the first few weeks.2
Skin and coat
A study published in the Journal of Veterinary Dermatology found dogs with atopic dermatitis showed significant improvement after omega-3 supplementation. A separate study found dogs supplemented with fish oil had a noticeably shinier coat compared to unsupplemented dogs — published in the American Journal of Veterinary Research.4
Brain and neurological health
DHA plays a specific role in brain and eye development in puppies, and may improve cognitive function in older dogs with canine cognitive dysfunction. The American Kennel Club notes research has shown omega-3 fatty acids can help treat canine arthritis and chronic kidney disease.1
What Type of Fish Oil to Look For
- Source matters: Salmon, sardine and anchovy oils are high in EPA and DHA. Cod liver oil is lower in omega-3s but high in vitamins A and D — which can cause toxicity at high doses, so it's not the best daily supplement choice.
- Not flaxseed oil: Plant-based omega-3s provide ALA, which dogs convert to EPA and DHA very inefficiently. Fish oil is more reliable.
- Formulated for dogs: Human fish oil capsules often contain doses too high or too low for dogs. Dog-specific products have clearer dosing guidance.5
- Freshness: Fish oil goes rancid. A good product should smell of fish, not of something that's been sitting in a warm garage. Store in a cool, dark place and use within the recommended timeframe.
Fish oil is one of the best supplements to add to your dog's diet. It supports heart health, promotes a silky coat, reduces itchy and flaky skin, and can help relieve allergies and joint pain.
— American Kennel ClubHow Much to Give
General veterinary guidelines recommend approximately 75–100mg of combined EPA and DHA per kg of body weight per day for joint support, though individual needs vary.3 Always follow the dosing instructions on the specific product and confirm with your vet — particularly for dogs with existing conditions, as fish oil can affect blood clotting at very high doses.