Can Dogs Eat Fish?

Picking the right food for your dog can get complicated. But, it doesn’t have to be!

Many dog foods base their protein source on either chicken, beef, lamb, or fish. This is when choosing the right type of dog food requires a deeper understanding of animal nutrition. 

In this article, we’re going to shed some light on fish!

Can dogs eat fish? Yes, definitely.

Could eating fish cause problems? Also, yes - everything has its disadvantages.

Here are some important facts about fish and how they can benefit your dog’s health.

1. What are the benefits of feeding your dog fish?
2. Does it matter what kind of fish you feed your dog? (*Spoiler - Yes!)
3. How to pick the best fish for your dog?
4. Fresh fish or Fish oil?

What are the benefits of feeding your dog fish?

Fish is an excellent source of protein that is unique from other animal proteins like poultry, beef, and lamb.

But, what sets fish apart?

Essential Fatty Acids - Omega-3

There are a lot of nutrients that your dog’s body can’t produce on its own, called “essential nutrients,” and these need to come from the diet! 

This is particularly important for essential fatty acids (EFAs).

Fish are unique because they have high levels of EFAs, specifically polyunsaturated fatty acids like Omega-3 (1). Both plants and seafood contain Omega-3 fats, but only Omega-3’s from seafood can directly provide two crucial polyunsaturated fatty acids:

1. Eicosapentaenoic acid (EPA)
2. Docosahexaenoic acid (DHA).

Why do fish have so much more Omega-3 fats than land animals? This comes down to the diet of fish. Since algae and seaweed are packed with Omega-3 fats, the fish that eat these can benefit!

The more marine plants a fish eats along the food chain, the more Omega-3 fats they tend to accumulate within their bodies. This also means different species of fish will have different levels of Omega-3 fats (2).

By incorporating fish into your dog’s diet, some advantages can include improved skin, coat, and nails.

More importantly, several studies show EPA and DHA have an anti-inflammatory role and reduce the risk of cardiovascular disease - both in dogs and humans (2).

Essential Vitamins - Vitamin D

Vitamins are organic molecules that your dog relies on for its cells to function properly - supporting growth, development, and energy metabolism.

Understanding exactly how fish function and their underlying physiology largely remains unknown. Fortunately, scientists over the last 50 years have made progress and learned that the hormonal regulation of fish depends on vitamin D as the primary messenger molecule (3). 

Fish accumulate vitamin D through their diet, then store it in their fat. This means fish species with more body fat also have more vitamin D. We can see this when we compare the vitamin D content of a fatty fish like salmon relative to a more lean fish like cod. Salmon can have 10x more vitamin D than cod (2). Such high vitamin D levels are both an advantage and a disadvantage, but we’ll talk about that in a second! 

The primary role of vitamin D is to increase the absorption of essential minerals like calcium and phosphorus from your dog’s digestive system and bring them into the blood. Both these minerals have significant roles in maintaining the structure and integrity of your dog’s bones.

However, unlike humans, dogs can’t absorb vitamin D through sunlight! This means your dog depends on adequate vitamin D supplementation through their diet (4).

Essential Amino Acids - Taurine

Amino acids are the building blocks of proteins. Mammals don’t have much use for intact proteins, so the digestive system breaks down proteins into accessible amino acids the body can utilize. 

Taurine is a vital amino acid that has recently received a lot of attention. 

Mainly, this interest comes from a potential connection between taurine deficiency and the onset of heart disease - called dilated cardiomyopathy (DCM). Some dog breeds are predisposed to DCM, but studies have also found breeds like the cocker spaniel and labrador retriever require a higher dietary source of taurine relative to other dog breeds (5).

Most animal tissues have taurine, but some fish are especially rich in taurine. In particular, white fish like cod can have 120mg/100g of taurine - nearly 2x the amount of taurine found in salmon and beef (2,6).

Fish are allergy friendly

An additional benefit fish-based diets provide is an alternative protein source for dogs with allergies.

Food allergies vary on a case-by-case basis, and sometimes it can be hard to tell if your dog has an allergy. Some dogs can show typical symptoms like poor digestion and irritated skin - both good indicators that your dog may be reacting to allergens in their diet!

A review of 19 different studies looking at 297 dogs found beef to be the most common dietary allergen (34%), followed by chicken (15%), then several other protein sources before finally getting to fish (2%) (7). This highlights the added benefit of a fish-based diet to help prevent allergies!

If you suspect an allergy, the best way to confirm is through allergy testing or a food elimination trial. An allergy can affect much more than just your dog’s fur, but can also impact your dog’s ability to use the nutrients they are eating - potentially leading to nutrient deficiencies! 

Contact your veterinarian and ask for some guidance in these situations. 

We’ll talk more about allergies in a future article!

Does it matter what kind of fish you feed your dog?

Yes, definitely!

There are thousands of fish species on this planet, but some types of fish provide a more balanced diet. Some fish are particularly enriched in certain nutrients that can benefit your dog’s health!

First, it would be a good idea to distinguish the differences between cold and warm water fish. 

Warmwater fish

Warmwater fish rely on an optimal water temperature to function properly. These fish typically live in tropical or freshwater regions with temperate/tropical climates. 

This also means they require less fat to insulate their bodies.

Coldwater fish

On the other hand, coldwater fish have more body fat. This allows them to regulate body functions despite a cold environment. Some examples of coldwater fish include:

• Salmon
• Tuna
• Sardines
• Mackerel
• Cod
• Pollock
• Haddock

The added fat that coldwater fish carry is extremely important because this is where essential fatty acids like Omega-3 fats are stored!

But, which coldwater fish might be the best choice for your dog?

How to pick the best fish for your dog?

The fat content of fish is an important factor in your dog’s health because this is where healthy Omega 3 fats are stored - helping reduce inflammation and improve cellular function. 

Does this mean we want to pick the fish with the most fat content?

Not necessarily. Here’s why.

Pick a fish with low to moderate fat content.

More fat content doesn’t make the fish a healthier option. 

Actually, it can lead to the opposite outcome - excess dietary fat leading to poor health!

Comparing the fat content of common coldwater fish, we see values ranging from 0.2g/100g of fat in a whitefish like haddock, to species like mackerel with upwards of 25g/100g of fat (2).

Often, salmon is a popular ingredient in dog food because of its high-fat content, but too much fat can leave your dog’s diet unbalanced!

Fatty Fish & Digestive Problems

Regardless of the fat type, excess fat can be problematic and lead to digestive problems. In excess, fats will accumulate in your dog’s gut and interfere with the proper absorption of nutrients. 

Excess fat can even damage the healthy gut bacteria that help your dog utilize certain nutrients in the first place.

This is a great example highlighting how more is not always better - even if it’s “healthy fats.”

Fatty Fish & Vitamin D Toxicity 

Earlier, we mentioned that fat is a primary storage site of vitamin D. By consistently feeding a high-fat fish diet, you’re also supplying vitamin D.

When given in excess, vitamin D can be toxic. 

In these cases, your dog will absorb too much calcium and phosphorous into their bloodstream, potentially leading to calcification and kidney damage.

Recently, Hill’s Pet Nutrition recalled 25 of their products for a formulation error resulting in 70x more vitamin D in their diets. Luckily, the signs of vitamin D toxicity were noticed by veterinarians after dogs were fed the Hill’s diet, initiating the recall and subsequent correction by Hill’s.

Pick a fish with essential minerals.

With so much focus going into vitamins, it’s easy for pet owners to overlook the importance of minerals!

Minerals are trace elements from the earth like calcium, sodium, potassium, magnesium, and several others. Your dog’s body can’t make these minerals, so they rely on an adequate supply from the diet to regulate everyday functions like muscle contractions, nerve transmission, and essentially every function of the cell.

If we don’t receive enough minerals through our diet, key enzymes will lose their function, muscles will lose the ability to contract, and blood wouldn’t be able to transport oxygen throughout the body. 

When we compare the mineral contents of different coldwater fish, we see that whitefish have a particular advantage over more fatty fish like salmon and mackerel. 

Iodine

In 1990, nearly 30% of the world’s population was affected by iodine deficiency - a preventable dietary concern that led to many neurological issues and hypothyroidism. Without iodine, we can’t produce essential thyroid hormones that regulate vital functions related to metabolism (9).

By 1999, most affected countries had implemented laws to produce iodized salt - ensuring people could receive dietary iodine. 

When it comes to dog food, we have to make sure your dog’s mineral requirements are met. The National Institute of Health mentions both fish and dairy products as rich sources of iodine. Since we aren’t typically feeding our dogs iodized salt, they have to get it from other sources!

Fortunately, lean whitefish species like cod and pollock provide high levels of iodine. For example, just 100g of cod provides approximately 120 μg of iodine. In comparison, fatty fish like salmon only have 12 μg of iodine (2).

Selenium

Selenium is a mineral that has a role in antioxidant function, but is also involved in metabolism, DNA synthesis, and reproduction (8). 

Scientists studying the effects of selenium deficiency found severe damage to the liver of rats - followed by hair loss, impaired growth, and infertility in newborn rat pups (8). 

Commercial pet food manufacturers include selenium in their diets to support a healthy metabolism, but achieving this balance with fresh homemade food can be difficult. 

Whitefish can provide a lean protein source rich in selenium - comparable to the selenium content of a more fatty fish like salmon (2). This way, we can limit excess fats while supplementing essential minerals like selenium by using whitefish in our recipes!

At NutriCanine, we believe the best way to prevent problems like excess dietary fat and vitamin D toxicity is to formulate our fish-based diets using fresh, lean whitefish. 

Whitefish like cod and pollock still provide moderate levels of fat, adequate amounts of vitamin D, Omega-3 fats, and essential minerals like iodine and selenium.

Fresh Fish vs. Fish Oil

If you’re considering including fish in your dog’s diet but aren’t ready to fully transition to fish-based meals, adding fish oil is a good start. 

Keep in mind these two major drawbacks when supplementing with fish oil:

1. Lacking Nutrients

Concentrated fish oil lacks many of the added proteins, vitamins, and minerals that would normally come with a whole fish diet!

Oily fish like anchovy, herring, and mackerel are common sources of fish oil, but we also see a lot of fish oil made from cod liver. Also, vitamin D is often included in many fish oil preparations, making it easier to supplement both at once!

1. Prone to Over-Supplementing

It’s easy to get in the habit of giving more fish oil than necessary. 

Unfortunately, this can become problematic because we risk over-supplementing with vitamin D. This is in addition to the potential irritation caused by excess fat on the digestive system and overall metabolic efficiency.

Veterinarians supplementing more than 53 mg/kg of combined EPA/DHA fish oil noted a common side effect of diarrhea. As the concentrated fat reaches the intestines, the fat molecules interact with the gut bacteria and produce byproducts that are rapidly excreted = diarrhea.

In addition, this added fat intake can cause stress on the pancreas. In chronic cases of excess fish oil supplementation, your dog may be at risk of pancreatitis (10). 

Omega fats are naturally unstable molecules that can react with oxygen to form harmful products - a process called lipid peroxidation (10). 

These reactive fats interact with cells in your dog’s body and cause structural damage that significantly impairs their function. That’s why we include several sources of antioxidants like berries and leafy greens into our NutriCanine recipes to help prevent lipid peroxidation (10).

Veterinarians at Tufts University suggest supplementing fish oil with a 2:1 ratio of EPA and DHA in cases of heart disease, but this is also a good maintenance dose for healthy cats and dogs.

The exact dosage depends on the size of your dog and the preparation of fish oil that you have. Check the product label to get a better idea!

Final Thoughts

Adding fish as a component to your dog’s diet is a great way to provide quality protein that comes with added benefits of healthy Omega-3 fats, vitamins, and minerals. 

Although fish oil can provide some healthy fats, we lose most essential nutrients through the extraction process. When possible, try feeding your dog a whole fish diet to utilize the many added nutrients needed to support your dog’s health.

If you’re thinking of transitioning your dog to our fresh fish recipes, send us a message and we can connect directly! 

Works Cited

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3. LOCK, E. J., WAAGBÃ, R., WENDELAAR BONGA, S., & FLIK, G. (2010). The significance of vitamin D for fish: a review. Aquaculture Nutrition, 16(1), 100–116.
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5. McCauley SR, Clark SD, Quest BW, Streeter RM, Oxford EM. Review of canine dilated cardiomyopathy in the wake of diet-associated concerns [published correction appears in J Anim Sci. 2020 Jul 1;98(7):]. J Anim Sci. 2020;98(6):skaa155. doi:10.1093/jas/skaa155
6. Purchas RW, Rutherfurd SM, Pearce PD, Vather R, Wilkinson BH. Concentrations in beef and lamb of taurine, carnosine, coenzyme Q(10), and creatine. Meat Sci. 2004 Mar;66(3):629-37. doi: 10.1016/S0309-1740(03)00181-5. PMID: 22060873.
7. Mueller RS, Olivry T, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res. 2016;12:9. Published 2016 Jan 12. doi:10.1186/s12917-016-0633-8
8. Zentrichová V, Pechová A, Kovaříková S. Selenium and Dogs: A Systematic Review. Animals (Basel). 2021;11(2):418. Published 2021 Feb 6. doi:10.3390/ani11020418
9. Delange F, Lecomte P. Iodine supplementation: benefits outweigh risks. Drug Saf. 2000 Feb;22(2):89-95. doi: 10.2165/00002018-200022020-00001. PMID: 10672891.
10. Lenox, C., & Bauer, J. (2013). Potential Adverse Effects of Omega-3 Fatty Acids in Dogs and Cats. Journal of Veterinary Internal Medicine, 27(2), 217–226.

URL’s:

1. (Kaur) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4190204/#:~:text=The%20term%20essential%20fatty%20acids,6%20(%CF%89%2D6)
2. (Torris) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6073188/
3. (Lock) https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2095.2009.00722.x
4. (Zafalon) https://pubmed.ncbi.nlm.nih.gov/33287408/
5. (McCauley) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7447921/
6. (Purchas) https://pubmed.ncbi.nlm.nih.gov/22060873/
7. (Mueller) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4710035/
8. (Zentrichová) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915357/
9. (Delange) https://pubmed.ncbi.nlm.nih.gov/10672891/
10. (Lenox) https://onlinelibrary.wiley.com/doi/10.1111/jvim.12033