Fish oil

Fish oil, EPA and DHA explained, with dog arthritis research, limits of the evidence and questions to ask before choosing a supplement.

Ingredient Directory›Fish oil

Ingredient & nutrient profile

Fish oil

A source of marine omega-3 fatty acids. Look beyond the words “fish oil” to the amounts of EPA and DHA and the evidence for the intended use.

Fat and OilDogCat
Ω3
Fish oilNutritional role • Research • Practical context
SpeciesDogs and cats
ScopeIngredient and nutrient context
AssessmentInitial evidence summary
Sources checked23 September 2026
Nutritional role

What it contributes

Fish oil is a mixture of fats, rather than a single active substance. EPA and DHA are the long-chain omega-3 fatty acids commonly discussed in clinical nutrition. The amount of oil in a capsule or food does not, by itself, tell you how much of either fatty acid it supplies.

Species and formulation

Read it in context

This profile is relevant to both dogs and cats, but the linked arthritis trial tested dogs only. Its findings should not be presented as evidence that the same product or dose treats arthritis in cats. Tufts clinical guidance also discusses fish oil in selected heart patients, with veterinary oversight. [2]

Research

What the evidence shows

Roush and colleagues conducted a randomised, double-blinded trial involving 38 dogs with osteoarthritis. Dogs received a fish-oil-enriched food or a control food for 90 days; the enriched-food group had improved weight bearing. This supports the tested dietary approach, not every fish-oil supplement or every joint-health claim. Our study entry now includes a full-text appraisal, with participant flow, direct comparisons and funding checked. [1]

Limits and safety

Before changing the diet

Discuss supplementation with your vet, particularly if your pet has a bleeding disorder or already eats a diet high in omega-3 fatty acids. Product concentration and quality vary. More oil is not automatically more beneficial, and a study of a formulated food does not provide a universal supplement dose. [2]

Food labels

Questions worth asking

Ask for EPA and DHA amounts per daily serving, the source of the oil, storage instructions and quality-control information. Count what the existing food supplies before considering an additional supplement.

Connected evidence

Explore the study

Study links follow your species selection. A shared nutrient profile may discuss more than one species.

Dogs • Controlled trial • Full-text appraisalFish-oil-enriched food and weight bearing in dogs with arthritisRead the study summary, methods and limitations.
Sources

References and review scope

  1. Roush et al. (2010), original study
  2. Tufts University: heart disease and nutrition, fish-oil guidance

This is an initial, source-linked overview, not a systematic review or a product endorsement. FEDIAF is the European pet-food industry federation; its guidelines provide formulation context rather than an independent clinical trial. Study-specific access limitations are stated above.

Product profiles with related ingredient context

These links show how to read a food declaration alongside this ingredient profile. They are not evidence that a product delivers the results of an ingredient study.

Dog · Raw / frozenNutriment Raw TurkeyRead the declared composition and evidence limits.Cat · Raw / frozenNutriment Cat Raw ChickenRead the declared composition and evidence limits.Dog · DryLily’s Kitchen Chicken & Duck Dry Dog FoodRead the declared composition and evidence limits.Cat · DryRoyal Canin Fit 32Read the declared composition and evidence limits.

Fish oil or fish protein hydrolysate?

These are different ingredients. Fish oil is the fat fraction; a protein hydrolysate contains protein-derived fragments. Read the fish protein hydrolysate profile for preparation differences and the limits of the canine behaviour evidence.