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Fins and Scales Oh My! All About Feeding Raw Fish

Updated: Dec 16, 2021

Yes, you can feed fish! While this protein may not have readily been eaten in the wild, one beautiful thing about human intervention, is the ability to provide more variety and unique proteins than a wild diet would provide. This is essential for preventing boredom and allergies/intolerances while providing a combination of nutrient profiles that contributes to balance over time! Just like the 100’s to 1000’s of eggs, fish lay, there is lots of information to cover when it comes to these scaly creatures!

Fish boasts the following benefits:

  • Anti-inflammatory (1) actions for the skin (2), hips and joints (3)

  • Aid in hairball relief (4)

  • Aid in heart health(5), brain health and eye health (6)

  • Prenatal care for puppies and kittens in the form of proper eye and brain development as well as tissue development (6, 7)

  • Nerve cell development (8)

  • May slow or prevent cancer by inhibiting important pro inflammatory and growth cells that aid in cancer growth (5, 9, 10)

  • Improve immune function (11)

  • Aid in reproductive health (12, 13, 14)

  • Aid Kidney function (15, 16)

  • Aid in weight loss (17, 18)

  • Lower/regulate blood pressure (19, 20)

While there are many options for feeding fish including, tinned/canned and in oil form such as capsules and pills, we want to feed fish raw, yes raw! It is included in a RAW diet after all! What is the difference though?

Raw fish contains fresh Vitamin D, components that are important for enzyme function, a complete fatty acid profile21 and most importantly selenium which is protective against mercury (22, 23), a common concern when consuming fish.

While tinned/canned fish is easier on the pocket books, contains less mercury (24) and has a longer shelf life than raw fish, it is not an ideal source of oils. When fish is tinned or canned, nutrients are depleted. Unbeknownst to many, tinned/canned fish is actually cooked, so many of the heat sensitive vitamins, minerals, fats, enzymes and proteins are destroyed, depleted or otherwise altered reducing many of the fish’s natural benefits (25,26, 27, 28).

Two other concerns with tinned/canned fish is the high sodium content (29,30) and Bisphenol A or BPA. Sodium is added to maintain flavor and texture of the product inside (31) while BPA is used for the linings of many canned products. The main concern with this is its ability to mimic estrogen32 causing a concern for disruption (33) and potential problems with reproduction, developmental and metabolic concerns (34)

Another popular option has been fish oils. These come in gel capsules as well as bottles. There is definitely convenience to this method, just pop a few gel capsules or a squirt of oil in the bowl and you are done! It’s also readily available at most grocery and pet stores as well, so there is no shortage in sourcing it.

However, there are several concerns. Oils are processed35. While this means these products most likely contain less mercury and other contaminants, the process can deplete important fatty acids that were originally extracted for its fat and omega properties. These products also do not often contain selenium but may contain other ingredients such as glycerin, gelatin, soy and food glaze.

The potency of fish oil and pills is higher than that found in raw fish. Because the product is processed, companies are able to concentrate and pack more in a smaller amount. The dark side of this higher potency however is that the benefits of omegas and fats are not as easily absorbed. Because the product is processed, essential fats and other components that help absorb the omega 3’s naturally are no longer present to activate these mechanisms (36)

Another concern we have with oils and pills is the oxidation rate. Oxidation not only can cause the product to quickly become rancid. Fish oils and pills often do not contain Vitamin E that otherwise would prevent oxidization both of the product as well as in the body. The danger of this is that Vitamin E is depleted in the body itself. The more fish oil you consume the higher the depletion (37). Oxidation especially over time can result in cellular damage, aging, increase the risk for cancer, cause reproductive problems, promote inflammation and many more side effects (38, 39, 40). Those that have Vitamin E added to their product are most likely artificial however (41).

In general supplements such as fish oil pills are loosely regulated with 1-3% of imported products being inspected (42, 43). There is some information out there that there are many fish oil products already on the shelves that ARE oxidized (44)! A study performed in 2013 analyzed the top 16 fish oils on the market. The results showed that 25% were already rancid! (45)

One final point to be aware of is that a majority of research done for fish oil is NOT done on commercial fish oils and pills, but rather on actual fish consumption (46)

Some raw feeders are vegan or vegetarian. While many are more than happy to provide their companion with a species appropriate raw diet that is meat based others feel that there are benefits to feeding plant based omega 3’s / fats. Unfortunately, plant omegas and animal omegas are NOT the same thing and they are NOT interchangeable.

Alrighty, we need to a get a little scientific here.

Fish based oils contain DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) with are long chained polyunsaturated fatty acids. Fats can be identified and classified not only by the number of carbons in the structure, but number and placements of bonds. All living things contain carbons and can be classified with the amount they contain. DHA contains 22 carbons with EPA containing 2047. Plant based fats/omegas such as coconut oil, flaxseed oil, chia seeds, leafy greens ect. contain shorter chains (18 carbons) of polyunsaturated fatty acids. While they contain alpha-linolenic acid or ALA they are absent of DHA and EPA47.

ALA is a fatty acid. It comes from plants and needs to be converted by a specific enzyme into useable forms such as DHA and EPA before the body can utilize it. Unfortunately, in our carnivore companions, this isn’t done efficiently. The conversion rate is less than 1%, therefore to get the same amount of EPA and DHA in fish for example you would need to eat A LOT of ALA (48)

In addition to this poor conversion rate, it’s been shown that fatty acids from marine sources not only elevate the fatty acid levels in the blood but remain such for 3 days or longer. (49) Plant fatty acids however are quickly absorbed and can only be found in the body for 10 hours after consumption before they are gone (50).

In short it seems that fatty acids from marine based sources are utilized and sustained much better than those found in plants. Furthermore, it is more beneficial to feed a source that is direct and to the point versus one that needs to be converted which may require more resources decreasing the efficiency.

So, we have identified that not only raw fish is the way to go but that marine based fats and oils are utilized and more beneficial to the carnivore body than plant based oils and fats. Let’s move onto some negative aspects and debunk some common myths and concerns surrounding the feeding of fish.

Cats, dogs and ferrets do not readily make DHA and EPA on their own (51), so it is essential that it is provided in the diet. While this can be a slight inconvenience there are many sources for fish that contain DHA and EPA.

The fatty acids found in fish are active blood thinners and anticoagulants (52), while this is helpful to reduce inflammation in hips, joints, skin conditions and cancers, this can be dangerous for those with blood disorders such as anemia or serious wounds.

It is essential that one knows where their fish is being sourced from. The biggest concern is farmed fish. The practice of farming fish is similar to other farmed animals like chicken and pigs. They are housed in containers with hundreds of other fish with little room to really move and get around. They often eat an unnatural diet typically including grains and can be fed hormones, antibiotics and even dyes to maintain color56, 53. This is no environment for an animal to grow and thrive to their natural potential. This also effects their otherwise natural benefits including omega content. In nature, there is a food chain of fish. the larger fish eat the smaller fish which eat the algae. The algae are where a lot of the omegas come from (53). In a farmed environment fish don’t have this food chain and thus their omega content is far inferior to natural raised fish.

Another concern is polychlorinated biphenyls or PCBs. Reports suggest that farmed salmon for example contain 16x more PCB levels than wild salmon! PCBs are cancer causing and neurodevelopmentally inhibitive chemicals that actually have been banned in the USA since the 1970’s54. The source is often the feed they are fed which is composed of lots of ground up fish to simulate the natural diet of fish in the wild. The goal is to increase fatty acid levels.

While there are consumption restrictions on wild caught salmon there are none on bought (farmed) salmon. Based on the EPA’s recommendations if these levels applied to farmed fish, the salmon would only be recommended to be consumed once a month!54 While this is a figure documented for humans, we can extrapolate this to our much smaller carnivore companions, as salmon is a common source of fish in the raw diet.

So, if we have all these things to be concerned with why feed fish?

One major reason is the meats our companion animals consume are deficient in Omega 3’s this is seen in the farmed fish as described above but also in other factory farmed animals like cows, chickens and pigs who are often not able to graze in the fields or exposed to natural sunlight (55, 56, 57). However, this is not limited to just factory farmed animals pasture raised and grass-fed meats can be depleted as well (58).

With soil being depleted of nutrients due to the use of pesticides, herbicides, GMO’s and other unnatural products, the grass that pasture raised and grass-fed herbivores are eating is thus also deplete (59). With this inferior grass, the production of omegas is also limited. That being said at the end of the day pasture raised and grass-fed meats are definitely much better than factory farmed animals. In general, grass-fed beef for example have 2-5x more omega 3 content than grain fed beef with the ratio of pro inflammatory omega 6 to anti-inflammatory omega 3’s in grass fed beef while is much lower than that of grain fed. 1.53:1 versus 7.65:1 respectively (58). Our companions have a diet more than adequate in omega 6’s. The proper balance is essential to ensure proper health and avoid inappropriate inflammation.

Time to debunk some common concerns about feeding raw fish to our companions.


Salmon Poisoning Disease is actually the infection of Nanophyetus salmincola

a fluke in salmon, trout, steelhead, and similar freshwater fish infected with the fluke. These fish are found in the Pacific Ocean from San Francisco to the coast of Alaska. This is not limited to the fish market but your average supermarket too. Symptoms include fever, depression, loss of appetite, vomiting, diarrhea and even death …signs similar to parvo virus. Only dogs can suffer from this, cats are not affected and luckily the flukes are visible to the naked eye. It should also be noted that this illness is only caused when the fluke itself is infected with an organism called Neorickettsia helminthoeca. (60)

Round worms can be a concern with fish as well. Often, they are found in Wild salmon (not farmed) and often removed during the gutting and cleaning process of marketed fish. Some may be missed however such as those found in the muscle and flesh of fish (61).

Tapeworms on the other hand are found in internal organs. These worms are common in fish from the Great Lakes area, southern Gulf and Artic (62). The easiest way to avoid this is not to feed the organs.

While talk of all these parasites/worms may seem freaky and frankly disgusting there is great news freezing fish at - 20°C for at least 2.5 days kills all worms found in fish (61).

There is even better news! Not only are parasites actually fairly rare in raw fish, if your carnivore companions have a healthy immune system then there typically is even less of a concern for parasites. An unhealthy animal will attract parasites due to an impaired immune system. These impairments can be due to stress from commercial processed diets, poor housing as well as toxin loads from vaccinations, flea, tick, deworming medications and much more. A non-impaired system, will be able to destroy or easily expel parasites from the body (63).

Fish is not natural part of the diet

Although this is very true, many foods we feed our companions are not naturally eaten in the wild such as cows, chicken, turkey, horse, alpaca etc. One awesome benefit of human intervention is the ability to provide lots of variety. This surely prevents boredom and helps provide a more complete nutrient profile contributing to a balanced diet.

Common allergen Fish actually is an important addition to the diet to reduce inflammation in the skin which can ease allergies and their symptoms. While some companion animals may very well have an allergy to fish it is very rare and other factors are much more to blame. This includes if the fish is in a commercial diet, if the fish contains GMOs, antibiotics, pesticides, herbicides, dyes or fed grains. One must also consider the animals environment, genetics, pollutants, drinking water and much more as factors leading to allergies.

The Bones are too small It is completely safe to feed raw fish as the bones are soft and surrounded by meat. It is cooked bones and those separated from the meat that become hazards due to splintering and obstruction whether that be in the throat or the intestines64.

There are a few real concerns raw feeders should be aware of. Biomagnification for example is one. Through this process an increase of hard metals, contaminants and mercury levels result. When the little fish is eaten by the small fish, which is eaten by the medium fish and then by the large fish, all the toxins from each of those fish below it is elevated in the big fish at the top of the food chain. So, the larger the fish the more likely it will contain toxins, hard metals and other such contaminants (65).

Depletion of Thiamin is another thing to be aware of.

Thiaminase is an enzyme found in some fish species, as well as some plants, bacteria and an African species of silk worm. The enzyme itself unfortunately breaks down and destroys vitamin B1 or thiamin which is essential in the body. Those deficient can suffer from neuropathic and cardiovascular problems (66) Thiaminase is present in many fishes and while a little fish here and there in the diet isn’t terrible, those that consume it in large amounts regularly can induce thiamin deficiency.

Cat’s should consume about 0.33 mg per day of thiamine while dogs should consume 0.11 mg. So, this should be accounted for when feeding fish in the raw diet.67

High carbohydrate diets such as most dry and canned foods require more thiamine as it will be needed to be used in large amounts to metabolize the carbohydrates (68)

The following contain Thiaminase:

  • Alewife

  • Anchovy, Broad-striped

  • Anchovy, Californian

  • Anchovy, Goldspotted Grenadier

  • Barb, Olive

  • Bass, White

  • Bonefish

  • Bowfin

  • Bream

  • Buffalo, Bigmouth

  • Burbot

  • Butterfish, American

  • Carp, Common

  • Catfish, Black Bullhead

  • Catfish, Brown Bullhead

  • Catfish, Channel

  • Cod, Black (species undetermined)

  • Dolphinfish, Common

  • Flagtail, Hawaiian

  • Goatfish, Manybar

  • Goatfish, Red Sea

  • Goatfish, Yellowstripe

  • Goldfish

  • Herring, Atlantic

  • Jobfish, Crimson

  • Jobfish, Green

  • Lamprey, Sea

  • Loach, Weatherfish

  • Mackerel, Chub

  • Menhaden, Atlantic

  • Menhaden, Gulf

  • Milkfish

  • Minnow, Fathead (“Rosy Red”)

  • Moray Eel, Southern Ocellated

  • Mullet, Flathead

  • Parrot, Regal

  • Queenfish, Doublespotted

  • Sardine, Razorbelly

  • Sauger

  • Scad, Bigeye

  • Sculpin, Fourhorn

  • Shad, Gizzard

  • Shiner, Emerald

  • Shiner, Spottail

  • Smelt, Rainbow

  • Snapper, Ruby

  • Stoneroller, Central

  • Sucker, White

  • Swordfish

  • Threadfin, Sixfinger

  • Trevally, Giant

  • Tuna, Skipjack

  • Tuna, Yellowfin

  • Whitefish, Lake

  • Whitefish, Round​

The follow fish do NOT contain Thiminase:

  • Amberjack, Greater

  • Ayu

  • Barracuda, Great

  • Bass, Largemouth

  • Bass, Northern Rock

  • Bass, Northern Smallmouth

  • Bloater

  • Bluegill

  • Cisco / Lake Herring

  • Cod, Atlantic

  • Crappie, Black

  • Croaker, Atlantic

  • Croaker, Spot

  • Cunner

  • Dogfish, Piked

  • Eel, American

  • Eel, Common

  • Flounder, Winter / Lemon Sole

  • Flounder, Yellowtail

  • Gar, Longnose

  • Glasseye

  • Haddock

  • Hairtail, Largehead

  • Hake

  • Hake, Silver

  • Halibut, Atlantic

  • Kawakawa

  • Kingfish, Southern

  • Lizardfish, Inshore

  • Mackerel, Atlantic

  • Marlin, Atlantic Blue

  • Mullet

  • Perch, European

  • Perch, Ocean / Redfish

  • Perch, Yellow

  • Pike, Northern

  • Plaice, American

  • Plaice, European

  • Pollock / Saithe

  • Pumpkinseed

  • Salmon, Atlantic

  • Salmon, Coho

  • Scad, Mackerel

  • Scad, Yellowtail

  • Scup / Southern Porgy

  • Sea Catfish, Hardhead

  • Seabass, Black

  • Searobin

  • Seatrout, Sand

  • Seatrout, Silver

  • Skate

  • Smelt, Pond

  • Soldierfish, Blotcheye

  • Sole, Common/Black

  • Sprat, European

  • Surgeonfish, Eyestripe

  • Tautog / Blackfish

  • Tilapia (various species)

  • Trout, Brown

  • Trout, Lake

  • Trout, Rainbow)

  • Trout, Sea

  • Tusk

  • Walleye

  • Weakfish, Sand

(72) The last thing to be aware of is the Mercury content. Mercury is common in most fish due to its presents in the air, soil and water that fish are exposed too. Fish readily absorb mercury in the form of methylmercury and is known to have a cumulative effect on the body which could lead to mercury poisoning (69).

70 ng/g or 0.07 ppm per day is considered safe (70, 71).

The follow fish contain less than 0.09 parts per million

  • Anchovies

  • Butterfish

  • Catfish

  • Clam

  • Crab (Domestic)

  • Crawfish/Crayfish

  • Croaker (Atlantic)

  • Flounder

  • Haddock (Atlantic)

  • Hake

  • Herring

  • Mackerel (N. Atlantic, Chub)

  • Mullet

  • Oyster

  • Perch (Ocean)

  • Plaice

  • Pollock

  • Salmon (Canned)

  • Salmon (Fresh)

  • Sardines

  • Scallops

  • Shad (American)

  • Shrimp

  • Sole (Pacific)

  • Squid (Calamari)

  • Tilapia

  • Trout (Freshwater)

  • Whitefish

  • Whiting

The following fish contain a moderate amount of mercury:

From 0.09 to 0.29 parts per million

  • Bass (Striped, Black)

  • Carp

  • Cod (Alaskan)

  • Croaker (White Pacific)