• Toni Miller
  • Dog Nutrition and Member Service Specialist

  • 5 mins read time
  • Something Smells Fishy: a Crash Course in Feeding Fish

    A popular ingredient in dry dog food and in a raw feeder’s bowl, fish has become a popular protein to feed dogs and is well-known for its positive impact on skin and coat health. One might ask: “why should I bother adding fish or fish oil to my pet’s bowl?” And for many, this is a completely valid question! Fish oil and fish supplements may simply act as a “bandaid” for a bad diet, so it’s important to ask ourselves why we supplement.

    People often add seafood in order to boost the level of Omega-3 fatty acids in our dogs’ diets, but why not just feed a food that already has a more balanced Omega 6:3 ratio? To put this into perspective, commercial dog kibble is notorious for being high in Omega 6 fatty acids and relatively low in Omega 3s. While many brands add in fish oil to counteract this, it can be hard to keep it shelf stable, and the ratios of Omega 6 can be higher than Omega 3s. Pet parents that feed fresh or raw food are less likely to experience this large disconnect, especially if they rotate the major proteins in their dog’s diet fairly frequently. But even so, different proteins have varying levels of Omega 3 and Omega 6 fatty acids - meaning some meats can be more inflammatory if fed too often. For example, chicken and other poultry, especially those fed a corn/grain-based diet, tend to have an extraordinarily large amount of O6 fatty acids and very few O3s. When fed in excess, this can cause things like itchy skin, ear infections, or other problems. Red meats, such as grass-fed beef and elk, tend to have a more balanced ratio of O6/O3s, but it can still be beneficial to add a bit of fish (foods we know are rich in Omega 3s) to your dog’s bowl every once in a while to help offset these ratios.

    And for those without easy access to whole fish, fish oil and krill oil has become all the rage to get those extra Omega-3s. Despite all the benefits though, there are some precautions we should take when adding seafood to our pets’ diets.


    Omega 3 Fatty Acids

    One of the reasons why many health-conscious pet owners add fish to their pet’s bowl is because it’s rich in Omega 3 Fatty Acids. This type of fatty acid helps reduce inflammation to promote joint health, and helps promote a healthy coat by reducing itchiness, rashes, and skin irritation. Omega 3s are made up of alpha-linoleic acid, EPA, and DHA. DHA is crucial for puppies, as it is known to support brain development in puppies. EPA has also been shown to reduce inflammation, promote a healthy cardiovascular system, and even slow cancer growth. For a more detailed look at the benefits of Omega 3s and the ideal Omega 6:3 ratio, you can check out this article on Omega Fats.

    Eye Health

    Fish can be a great source of vitamin A which helps promote good vision in low light, and can slow down age-related sight loss. Cod and salmon are a great source of vitamin A, also known as retinol, and are some of the most common fish available on the market.

    Immune System Health

    Fish is high in iron, zinc, and selenium - all of which contribute to a healthy immune system. Iron aids in the production of red blood cells - lack of iron can lead to your dog feeling weak and tired. Zinc is an antioxidant that helps the body make new cells and enzymes, and that helps keep the thyroid and digestive system functioning properly. Zinc deficiencies can lead to a slew of problems with digestion, organs, and the immune system. Selenium is necessary for a functioning immune system and thyroid gland.


    The benefits of feeding fish are abundant, but it is important to remember that you can always have too much of a good thing. Feeding too much fish or fish oil can lead to an over- or under-absorption of certain vitamins, which can ultimately hurt your dog even when you were just trying to help. So let’s examine the types of vitamin toxicity you should be aware of, and how to avoid it.

    Vitamin E Deficiency

    Back in 2014, someone published a blog post on a pet forum about their overwhelmingly negative experience with fish oil and how it nearly killed their then 3-year old Neapolitan Mastiff. Like many pet owners, they were supplementing their dog’s diet with fish oil (and glucosamine) to promote healthy joints and a beautiful coat. However, their dog’s condition started deteriorating, to the point where he was pretty much paralyzed in his back legs, and was exhibiting arthritis symptoms despite only being 3-years young. Upon further investigation, they realized their dog was suffering from vitamin E deficiency. They began supplementing with vitamin E and stopped supplementing with fish oil altogether, and it wasn’t long before their pup was back to his normal, athletic, and energetic self.

    So how can one act of love go so wrong? What many don’t know is that fish oil needs vitamin E in order to be processed by the body. When too much fish oil is fed, this results in vitamin E deficiency, which can manifest as:

    • Severe pain

    • Hyper-sensitivity to pain

    • Edemas (fatty lumps)

    • Cataracts

    • Lameness/premature arthritis

    • Premature aging

    But don’t jump the gun - this doesn’t mean that all fish is bad or that we shouldn’t ever add seafood to our dogs’ diets. We just have to be more conscious of two things - how much we supplement, and why we supplement.

    Vitamin A Toxicity

    Vitamin A is an essential vitamin for dogs, cats and humans - it’s a fat-soluble vitamin that is responsible for good vision, growth, and healthy immune and cell function. However, vitamin A toxicity, also known as hypervitaminosis A, can lead to some pretty serious side effects like stiffness, immobility of joints, and arthritis. This type of toxicity is typically caused by eating too many vitamin A-rich foods, such as organ meat, or by consuming supplements high in vitamin A, like cod liver oil. Generally, a dog’s condition will improve if the diet is changed or supplementation is stopped, but damage to the joints and bone formation are often irreversible and do not improve with treatment. It is important to note that most regular fish oils are rich in Omega-3s but DO NOT have much vitamin A or D, as these oils are extracted from the flesh of oily fish species. On the other hand, LIVER OILS come from the liver of fish and have fewer Omega-3s and are a rich source of vitamins A and D. It is with liver oils in particular that you have to be concerned about vitamin A toxicity.


    Vitamin E Imbalance

    One of the big differences between feeding whole, fresh fish and feeding fish oil is the imbalance between vitamin E and the Omega 3 fatty acids. Any fish you feed will contain some level of “oil,” which will need to be processed by your dog’s body using vitamin E. Fortunately, whole fish contains vitamin E naturally, making it less likely to cause deficiencies. But when it comes to fish oil, the natural source of vitamin E is killed off during any freezing, cooking or canning - leaving all the Omega 3s intact with no extra vitamins for the body to process it with. Assuming you supplement with fish oil daily, it’s possible your dog could deplete their vitamin E supply simply from trying to process all the oil!

    And while you can certainly add extra vitamin E to your dog’s diet to combat the drain from fish oil, there are also risks of blood thinning and the impact on other medications to consider before taking the “double-supplementation” route.

    The Trouble with Oxidation

    One of the biggest issues with fish oils compared to whole fish is that fish oils leave Omega-3 fatty acids vulnerable to oxidation. Omega-3 fatty acids are volatile and become unstable once exposed to oxygen, causing them to become rancid and damaging. Rancid Omega-3s can accelerate cancer cell growth, increase inflammation, and exacerbate allergy symptoms. However, fresh, non-oxidized Omega-3s can still provide the benefits of reduced inflammation and help to curb cancer cell growth.

    Most fish oils have already oxidized before they even hit the pet store’s shelves. Feeding fresh, whole fish on occasion is often preferable to purchasing fish oil, but for those interested in the convenience of oils, there are several steps you can take to look out for high quality, non-oxidized, fish oil for pets.

    • Pay attention to where the fish is sourced from in oil form and when feeding fresh, whole fish (more on this below!)

    • Buy fish oil that is packaged in a dark, glass bottle instead of a plastic one (plastic accelerates oxidation, and pumps do not provide an oxygen tight seal)

    • Keep your oil refrigerated and use it quickly

    Ethical Sourcing

    Paying attention to where the fish is sourced from is incredibly important when considering the benefits and risks it can have when feeding it to your dog. Most fish oil products will list the source of their fish on the bottle, but if it isn’t listed, you can (and should) reach out to the manufacturer to ask where the fish was caught, and where the oil was processed. There are two important things to note: where the fish came from, and what kind of fish it is.

    When evaluating fish oils, you may be faced with a choice between wild-caught or farm-raised fish. Each has its own set of pros and cons! Farm-raised fish can have somewhat less exposure to mercury than their wild counterparts, but they are more susceptible to absorbing other forms of pollution (i.e., pesticides, antibiotics) and are at higher risk for disease due to unsanitary farming conditions. However, farm-raised fish are also higher in Omega-3 fatty acids compared to their wild counterparts, and the levels of any toxins in farmed fish are often monitored and must remain within acceptable limits. As for wild-caught fish, they contain more mercury than farmed fish and can harbor parasites (take precautions against this if feeding fresh fish). With all of that said, either is often a safe option - wild and farmed fish are both carefully monitored for toxins, and they are both rich sources of beneficial omega-3 fatty acids.

    The second thing to look out for is what kind of fish the oil is extracted from. Ideally, you should look for an oil that uses small, cold water fish that were sustainably fished from the wild. Fish oils made from herring, anchovies, sardines, mackerel, or salmon are generally safer than things like tuna, swordfish, or marlin. Larger predatory fish often have higher levels of mercury, as it “bioaccumulates” while they eat smaller fish over time. Mercury poisoning can result from too much mercury, and can include symptoms such as loss of coordination, irritability, depression, muscle weakness, and skin inflammation. Small oily fish still contain small amounts of mercury, as it’s not completely avoidable, but the quantity is much smaller and safer compared to that of larger fish.


    So now that you know the differences between fish oil and whole fish, what kinds of fish are appropriate to feed your dog?

    Small vs Large Fish

    I already mentioned this above, but you should always opt for small, fatty, oily fish that are wild caught. It is best to avoid farmed fish and predatory fish. Farmed fish are often given hormones and drugs to prevent disease, and many predatory fish have longer life spans and can accumulate mercury in their system, leading to heavy metal toxicity. Additionally, if feeding fresh fish (wild caught or not), it is important to freeze them for at least a week before feeding to kill any potential bacteria or parasites that might be present in the fish! You likely won’t have to worry about this step if you buy fish “flesh” (no organs) from the grocery store. But if you purchase whole fish, or fish from a local market, it might be worth it to take the extra precaution. Be sure to avoid feeding organs and only feed the flesh of the fish to avoid tapeworms. If feeding canned fish, freezing is not necessary.

    Some great options for whole fish include:

    • Sardines

    • Salmon

    • Smelt

    • Anchovies

    • Herring

    • Mackerel

    • Cod

    • Pollock

    Fish to avoid include:

    • Tuna

    • Tilapia

    • Swordfish

    • Walleye

    And what if your dog doesn’t like fish? Well, you have a few options. You can look into some of the fish alternatives listed below, or you can get creative with how you feed them. Fresh fish can be cut into small pieces and mixed with your dog’s normal food or a special treat. You can also opt for freeze dried or air dried fish - this will allow you to crumble the fish into a fine powder that can easily be hidden in most dog foods.


    A bivalve is a type of freshwater and marine mollusk that have laterally compressed bodies enclosed by a shell made of two parts. When it comes to feeding bivalves, green lipped mussels are generally regarded as safe to feed, but you should be cautious when feeding other kinds of mollusks.

    Green lipped mussels are a type of bivalve that are naturally anti-inflammatory with no known side effects, are full of omega 3 fatty acids, and help support immune and circulatory system functions. They are a great option if you don’t want to feed fish, and can be fed raw or in a powdered form as a meal topper! GLM have been shown to improve joint mobility, cartilage maintenance, and cardiovascular health and make a great addition to any pet’s diet!

    However, other types of bivalves like clams, oysters, and other mussels should be fed with caution. Though they are generally rich in important nutrients like protein, zinc, and selenium, the risk of toxins from microalgae are a common concern. Temperate water and seasons can affect the level of toxins in seafood, so it’s important to make sure that any seafood you feed comes from clean, cooler waters where suppliers test their seafood for contamination.



    Phytoplankton is a tiny micro-algae that contains high levels of both DHA and EPA Omega 3 fatty acids. These fats help support your pup’s immune system, joint health, and cognitive function. When feeding phytoplankton, be sure to source from a brand where the phytoplankton are grown sustainably, are free from radiation and heavy metals, and are free of fillers. For more information on phytoplankton, you can check out our other article here.

    Underwater Greens

    While both of the options below are safe to feed in small amounts, it is important to take breaks when supplementing to allow your dog’s body to rest and not be overloaded with supplements. Large amounts of kelp has the potential to cause arsenic poisoning, while excess amounts of seaweed can lead to a buildup of mercury. Remember - everything is good in moderation, and there can be too much of a good thing.


    Kelp is a type of seaweed that comes from cold water areas and is usually fed as a dry powdered supplement. It is rich in vitamins and minerals like calcium and potassium, and can be beneficial for skin and coat health and healthy teeth and gums! One of the key benefits from kelp is that it is rich in iodine - this helps support thyroid health and can help manage your dog’s glandular functions. It’s a great, easy to feed supplement with tons of amazing benefits and fewer risks!


    Seaweed can be very high in minerals like protein, fiber, vitamins, and amino acids. Sheets of seaweed (nori) can be crumbled over your dog’s food, or you can add powdered seaweed to help support various organ health, as well as to help soothe the gastrointestinal system. It is best to avoid unprocessed seaweed and wild seaweed, as these can lead to intestinal blockages and cause salt poisoning due to their high salt content. Also, be sure to avoid red seaweed, as this is often harvested for carrageenan - a substance extracted from this type of seaweed and used as a thickening agent or emulsifier that may be tied to various health issues.

    The benefits of feeding seafood are well known, but with so many choices on the market, it can be overwhelming to find the right choice. It is important to be aware of the pros and cons of feeding seafood, and any potential side effects of the many options presented to us.

    Fish oil has a lot of caveats (oxidation, vitamin a toxicity, vitamin e deficiency) and can often be more risky than feeding whole, fresh fish or other healthy alternatives, so it is always best to opt for other supplements when possible. In a pinch, fish oil can be a good source of Omega 3 fatty acids, though it is important to consider sourcing, packaging, and proper storage when picking a fish oil brand for your dog.

    If you choose to opt for fresh fish, you are often given the choice between wild-caught and farmed fish. Farmed fish can be higher in omega-3 fatty acids, but are at risk of having antibiotics in them as a result of increased risk of illness. On the other hand, wild-caught fish are a more natural option, but they can be higher in mercury and are at risk of contracting parasites. Either is a great way to add extra omega-3s to your dog’s diet, just pay careful attention to sourcing, avoid feeding large predatory fish, and freeze all fish for at least a week to kill potential parasites.

    Finally, if you opt for a seafood alternative like kelp, phytoplankton, or seaweed, remember to give your dog a break every now and again from supplementation so as not to overwhelm their body. In the end, always be sure to ask yourself why you are supplementing, and remember to avoid over-supplementation with any food.