Why Fish? The Science Behind Fish-Based Nutrition for Dogs

For generations, chicken and beef have been among the most familiar ingredients in dog food. But as our understanding of canine nutrition has developed, fish has emerged as a particularly interesting source of high-quality protein — not simply because dogs enjoy it, but because of the nutritional compounds it naturally provides.

For dogs experiencing digestive sensitivities, skin and coat problems, joint stiffness or difficulties maintaining a healthy weight, what goes into the bowl deserves serious consideration.

And there is a growing body of scientific research behind the role marine ingredients can play in canine health.

1. Fish provides high-quality, digestible protein

Protein is fundamental to a dog's health. It provides the amino acids required for maintaining and repairing muscle and other tissues and supporting numerous physiological functions.

Fish is an excellent source of essential amino acids, and research into fish ingredients for pet food has demonstrated high protein quality and digestibility. Research examining fish meals and fish protein ingredients found lysine digestibility averaging approximately 90%, while salmon protein hydrolysate was particularly palatable to dogs.

For owners of dogs with digestive sensitivities, however, another characteristic of a fish-based diet may be particularly relevant: it offers an alternative to some of the animal proteins most commonly associated with adverse food reactions.

2. Chicken or beef doesn't suit every dog

Food allergy and food intolerance are frequently discussed together, although they are not the same thing and gastrointestinal or dermatological symptoms can have many different causes.

Nevertheless, there is good scientific evidence that certain food proteins feature disproportionately in confirmed adverse food reactions in dogs.

A review of published studies examined 297 dogs in which offending food allergens had been identified through dietary restriction followed by re-challenge.

The most frequently reported allergens were:

Beef – 34%
Dairy – 17%
Chicken – 15%
Wheat – 13%
Lamb – 5%
Fish – 2%

This doesn't mean that 34% of all dogs are allergic to beef — they aren't — nor does it mean that fish cannot cause an allergy. Rather, among the dogs in these studies with confirmed cutaneous adverse food reactions, beef and chicken were considerably more frequently identified as triggers than fish.

That distinction matters.

For a dog experiencing recurring digestive or skin problems, changing the dietary protein can therefore be an important avenue to discuss with a veterinarian.

3. Fish is naturally rich in the Omega-3 fatty acids EPA and DHA

Perhaps the most interesting nutritional advantage of oily fish and fish oils is their naturally occurring long-chain Omega-3 fatty acids, particularly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).

These fatty acids are incorporated into cell membranes and have important biological functions throughout the body.

This is one of the reasons marine nutrition has been studied in areas ranging from joint health and inflammation to skin, cardiovascular health and cognitive development.

And importantly, this isn't simply theoretical.

4. The evidence for joints and mobility is particularly compelling

Omega-3 fatty acids from fish oil have been extensively investigated in dogs with osteoarthritis.

In one randomised, double-blinded controlled clinical trial involving dogs with osteoarthritis, researchers compared dogs eating a control food with dogs receiving a food containing fish-oil Omega-3 fatty acids.

After 90 days, the dogs eating the Omega-3-enriched food showed a 5.6% improvement in peak vertical force — an objective measure of weight-bearing — compared with 0.4% in the control group.

Even more strikingly, 82% of dogs receiving the Omega-3 food improved their peak vertical force, compared with 38% of dogs receiving the control food.

Other controlled canine studies have also investigated fish-derived Omega-3s in dogs with naturally occurring osteoarthritis.

This does not make fish food a treatment for arthritis, and dogs experiencing pain or mobility problems should always receive appropriate veterinary care. But it provides compelling evidence for considering marine Omega-3 fatty acids as part of the nutritional support of joint health.

5. Skin and coat health

The skin is the body's largest organ, and nutrition plays an important role in maintaining its normal structure and function.

EPA and DHA have consequently attracted considerable interest in veterinary dermatology.

Controlled canine research has examined Omega-3 supplementation in dogs with poor coat quality as well as dogs experiencing pruritic skin disease.

That doesn't mean an itchy dog simply needs fish oil. Itching can have numerous causes — including environmental allergies, parasites, infections and adverse reactions to food — and persistent symptoms warrant veterinary investigation.

However, providing appropriate essential fatty acids through the diet can help support normal skin function and coat quality.

6. What about recurring ear problems?

This is another area where careful language matters.

Recurring ear inflammation is not itself proof of a food allergy. However, ears are a common site of lesions in dogs with atopic dermatitis.

A multicentre study of 552 dogs with atopic dermatitis found that the paws were affected in 62% of dogs, the ventral body in 51%, ears in 48%, and the face in 39%.

Dogs experiencing recurrent ear disease should therefore be properly assessed by a veterinarian rather than repeatedly changing foods without identifying the underlying problem.

Where an adverse food reaction is suspected, however, dietary investigation may form part of that process.

7. Fascinating Irish research: Teagasc's work on marine ingredients for dogs

Some particularly interesting research is happening here in Ireland.

Dr Maria Hayes and colleagues at the Teagasc Food Research Centre have been investigating the potential to transform fish-processing by-products into valuable functional ingredients for animal and human nutrition.

The Teagasc Pet Ageing and Wellness (PAW) project specifically investigated fish-processing by-products as nutritional and health ingredients for dogs, with a focus on ageing and cardiovascular health.

Teagasc subsequently developed fish protein hydrolysate ingredients and tested them in dog foods.

According to Teagasc, clinical trials in dogs consuming biscuits containing these marine protein hydrolysates demonstrated:

• a significant reduction in blood pressure compared with controls
• reduced weight gain compared with controls
• good digestibility
• improved palatability compared with controls

The work is particularly exciting because it goes beyond thinking of fish simply as “protein”.

Fish contains biologically active compounds that researchers are investigating for potential anti-hypertensive, anti-inflammatory and metabolic effects.

In 2022, Dr Hayes and Dr Paula O'Connor received a Teagasc START Award for their Pet Aging and Wellness work. Teagasc describes their fish protein hydrolysate as a functional pet ingredient with potential applications in helping prevent high blood pressure and weight gain and potentially influencing inflammation.

More recent Teagasc research has continued to explore the potential of fish-processing by-products and their bioactive compounds.

8. Nutrition and healthy weight

Maintaining an appropriate body condition is one of the most important things an owner can do for a dog's long-term health.

This is particularly relevant for breeds genetically predisposed to weight gain.

One large UK study involving more than 22,000 dogs found that approximately one in 14 dogs was recorded as overweight by their veterinary practice during a single year, with Pugs, Beagles, Golden Retrievers and English Springer Spaniels among the breeds at increased risk.

There is even a fascinating genetic component in Labradors. Researchers have identified a deletion affecting the POMC gene that is associated with body weight in Labrador Retrievers.

For these dogs, carefully controlled energy intake and appropriate nutrition are particularly important.

Fish itself isn't a weight-loss treatment. Different fish species and formulations vary substantially in fat and energy content. However, appropriately formulated fish-based diets can provide high-quality protein while allowing fat and calorie levels to be tailored to life stage and weight-management requirements.

9. A more sustainable protein source can have another advantage

There is also an environmental dimension.

A considerable proportion of nutritious material generated during fish processing has historically been treated as a low-value by-product.

Research at Teagasc has been specifically concerned with recovering these valuable marine proteins and bioactive compounds and turning them into functional ingredients.

This creates the possibility of doing two things simultaneously: providing valuable nutrition while making better use of an existing food resource.

It is the principle behind Harley & Marley's own approach.

Our food is made in Ireland using freshly prepared Irish fish, including fish sourced from Kilmore Quay. Rather than relying on chicken or beef as an additional animal protein, our recipes are deliberately fish-based.

So, should every dog eat fish?

Not necessarily.

There is no single perfect protein for every dog, and claims that one ingredient will “cure” allergies, arthritis, digestive disease or skin conditions should be treated with caution.

But the scientific case for fish as a canine nutritional ingredient is strong.

It provides high-quality protein. Marine ingredients supply the long-chain Omega-3 fatty acids EPA and DHA. Controlled trials have demonstrated meaningful effects of fish-derived Omega-3s in dogs with osteoarthritis. Fish represents an alternative animal protein for dogs that react to more commonly fed proteins. And emerging research — including pioneering work by Teagasc here in Ireland — suggests marine proteins may have functional properties extending well beyond their basic nutritional value.

For us, that is the real argument for fish-based nutrition.

Not a marketing trend.

Just very good ingredients, supported by increasingly good science.