Thiaminase- What is it & Which Fish Contain It

January 3, 2021

After doing my monthly meal prep at the start of the weekend, I shared my 30-day prep with all of you and pointed out the particular species of sardines used. I did this because the sardines I used are not amongst the species known to contain thiaminase, listed in the Nutrient Requirements of Warmwater Fishes & Shellfishes, hence, there was no issue storing the fish alongside the rest of my prepped raw meats. 

But wait, what does that mean? Are there fish you aren't supposed to store with raw meat?

Apparently so. That is, according to many raw feeding blogs and some canine nutritionists. They write that storing fish, known to contain thiaminase, with other raw meat for prolonged periods of time, will destroy the thiamine present in the fresh meat- hence not including them in your meal prep containers, instead, pack them separately. 

This is something I have seen shared numerous times and quite frankly, I thought nothing of it as none of the fish I currently feed are known to contain thiaminase. I took this assertion as fact because it wasn't something I needed to worry about & I saw numerous credible sources quoted, though I did not take the time to actually look into the case studies that were shared. Big mistake

After posting my meal prep to social media, I took a step back to take some time to read up on the evidence that demonstrated there to be a significant depletion of thiamine after prolonged exposure to thiaminase. What I found the case studies to actually reveal, is shared below. But first, we must start with a basic question...

What is thiamine? 

Commonly known as Vitamin B1, thiamine is a water-soluble organic compound that acts as a cofactor in carbohydrate catabolism. Mammals synthesise thiamine through their gut bacteria, however the most significant amount of thiamine is ingested through diet. Given that it is not a fat-soluble vitamin, there is virtually no toxicity from excess ingestion of thiamine, and rather excess amounts will be stored in various organs and parts of the body as reserves in case of depleted thiamine amounts in the diet due to unavailability for a certain period of time.

A minor deficiency in thiamine will lead to increased inefficiency in metabolising carbohydrates, a major energy source for both humans and dogs for example. Symptoms of a minor deficiency are mainly characterised by lethargy. A severe deficiency will lead to neurological symptoms. 

In humans, a severe deficiency leads to Korsakoff syndrome, which is characterised by chronic memory impairment due to damaged brain structures involved in memory formation and function (hypothalamus and thalamus). Loss of memory, inability to make new memories, confabulation, and hallucinations are the most common neurological symptoms of Korsakoff syndrome. Canine species will also suffer neurological symptoms from a severe thiamine deficiency. However, attaining the atypical metabolic states where such a severe deficiency develops is extremely rare. To illustrate this point, the prevalence of Korsakoff syndrome is approximately only 1-2% of the general population in the United States, per the NORD (National Organisation for Rare Disorders).

Thiaminase vs. Thiamine

Proteins that catalyse, or increase the efficiency of biochemical reactions are called enzymes. Enzymes are extremely important for practically every reaction and process that is undergone in the body. Without them, complex life forms would never be possible. Enzymes work by binding to specific molecules that are called reactants. 

In the most simple form, one enzyme will recognise one specific molecule as its reactant, bind to that molecule once it knocks into it, and then hold that reactant in its active site in order to chemically alter the molecule and complete the reaction.

Thiaminases are a family of enzymes that specifically bind to thiamine and cleave the thiazole functional group, rendering thiamine metabolically inactive. The biological purpose for thiaminase is not well defined, as thiaminase essentially inactivates an important vitamin for proper metabolic function. The reaction mechanism is illustrated below (Costello et al, 1996).


The left hand side of the chemical reaction shows the reactant (thiamine), the arrow represents the action of Thiaminase I, and the right hand side shows the products of the reaction.

Dietary Concerns

Many species of fish contain thiaminase and as a result, have been marked as potential risks for vitamin B deficiency if incorporated into a dog’s diet. 

In a commonly cited paper (source) investigating the severe thiamine deficiencies experienced by a team of 12 sled dogs, the inherent risk of an all-fish diet is duly noted. The dogs in this case study experienced severe deficiency after being fed fresh frozen carp and suckers over the course of approximately 6 months before symptoms arose. Necropsies of the dogs revealed depleted reserves of thiamine as a result of the all-fish diet which were consistent with neurological symptoms and ultimately the deaths they experienced.

What this case study teaches us is not that feeding these thiaminase-containing fish varieties is problematic. Rather, it showed that excess use of raw fish without dietary variety in dogs that have significant metabolic needs (such as sled dog) is the problem. The golden rule of all diets is moderation. Excess of anything is problematic in one way or another.

Other commonly cited articles, such as “The Effect of Freezing Rate, Storage, and Cooking on some B-Vitamins in Beef and Pork Roasts” (source) investigate the non-thiaminase related ways to deplete thiamine in meat. The results highlighted that the cooking of beef and pork roasts will lead to loss of vitamin B levels, which is why raw feeding is a favourable method of feeding from a standpoint of maximising water soluble vitamin retention. Again, this article does not investigate the activity of thiaminase or the effect of fish on dietary levels of thiamine.

Finally, “The Thiamine Status of Adult Humans Depends on Carbohydrate Intake” (source), another oft used article, only concludes that increased carbohydrate intake in a 12 person sample group demonstrated lowered thiamine levels in the serum— as is expected when a cofactor (kept at a constant level) of a metabolic process is increasingly used up. The purpose of thiamine is to help the body break down carbohydrates such as glucose, fructose, and lactose after all.

Citing of these articles in discussions of thiaminase risk as a result of incorporating raw fish in the diet seems to be missing the mark. None of these studies demonstrate definitive evidence of a significant concern for thiamine deficiency when feeding raw fish in moderation. None of these studies explore the inactivation of thiamine through physical contact between raw fish, raw meat and vitamin B supplements.


In conclusion, based off of these case studies, there seems to be little to worry about when it comes to thiamine, thiaminase, and using raw fish in one’s diet. 

When it comes to a dog’s raw fed diet, variety of meats and macronutrients is a pillar of nutrition that should be respected at all costs. Remember the golden rule of nutrition and avoid excess/lack of variety.

 If you want to be extra safe with the levels of vitamin B1 your dog receives from a weekly diet that is more concentrated in raw fish, add some vitamin B1 supplement to the diet. There is no reaction occurring between the cellular thiaminase and powdered/encapsulated thiamine you add to the bowl. Enzymes can only “inactivate” as much substrate as there are enzymes, therefore adding more thiamine is a perfectly safe way to ensure sufficient intake.

The only relevant condition to consider here is when a thiaminase-containing food is ingested along with a thiamine source. There is no significant chemical reaction occurring when meats or food are coming into contact in the fridge or bowl to be served. Chemical reactions occur in aqueous mediums (water containing) and mechanical digestion through mastication of these foods increases the surface area and physical availability that can be used for reaction. As a result, in order to avoid thiaminase interaction with a vitamin B supplement or thiamine containing food, then it is advisable to space the ingestion of the foods.

Now, is there anything wrong with continuing to separate your thiaminase-containing fish from the rest of your raw meat when meal prepping? 
Absolutely not.

Is there anything wrong with continuing to steer clear of thiaminase-containing fish and only feeding fish known to be free of those enzymes? 
Absolutely not.

So can I freeze my thiaminase-containing fish with my raw meat? 
Enzyme function works on a temperature curve. At very cold temperatures (ie. freezing temps.) molecular particles move very slowly. For that reason, enzymatic reactions are virtually non-occurring at freezing temperatures. On the flip side, at extremely high temperatures, enzymes will denature (ie. during cooking) and also become inactive. Thiaminase is an enzyme that functions optimally at room temperature (~ 25 ºC) and inactive at freezing temperatures (0 ºC & below).  As a result, there is no concern for thiaminase to be breaking down thiamine while stored in your freezer. 

The following fish have been reported to contain thiaminase:

Alewife (Alosa pseudoharengus)
Anchovy, Broad-striped (Anchoa hepsetus)
Anchovy, Californian (Engraulis mordax)
Anchovy, Goldspotted Grenadier (Coilia dussumieri)
Barb, Olive (Puntius sarana)
Bass, White (Morone chrysops)
Bonefish (Albula vulpes)
Bowfin (Amia calva)
Bream (Abramis brama)
Buffalo, Bigmouth (Ictiobus cyprinellus)
Burbot (Lota lota)
Butterfish, American (Peprilus triacanthus)
Carp, Common (Cyprinus carpio)
Catfish, Black Bullhead (Amieurus melas)
Catfish, Brown Bullhead (Ameiurus nebulosus)
Catfish, Channel (Ictalurus punctatus)
Cod, Black (species undetermined)
Dolphinfish, Common (Coryphaena hippurus)
Flagtail, Hawaiian (Kuhlia sandvicensis)
Goatfish, Manybar (Parupeneus multifasciatus)
Goatfish, Red Sea (Mulloidichthys auriflamma)
Goatfish, Yellowstripe (Mulloidichthys samoensis)
Goldfish (Carassius auratus)
Herring, Atlantic (Clupea harrengus)
Jobfish, Crimson (Pristipomoides filamentosus)
Jobfish, Green (Aprion virescens)
Lamprey, Sea (Petromyzon marinus)
Loach, Weatherfish (Misgurnus)
Mackerel, Chub (Scomber japonicus)
Menhaden, Atlantic (Brevoortia tyrannus)
Menhaden, Gulf (Brevoortia patronus)
Milkfish (Chanos chanos)
Minnow, Fathead (“Rosy Red”) (Pimephales promelas)
Moray Eel, Southern Ocellated (Gymnothorax ocellatus)
Mullet, Flathead Mugil cephalus)
Parrot, Regal (Scarus dubius)
Queenfish, Doublespotted (Scomberoides lysan)
Sardine, Razorbelly, Scaled Sardine (Harengula jaguana)
Sauger (Harengula jaguana)
Scad, Bigeye (Selar crumenophthalmus)
Sculpin, Fourhorn (Triglopsis quadricornis)
Shad, Gizzard (Dorosoma cepedianum)
Shiner, Emerald (Notropis atherinoides)
Shiner, Spottail (Notropis hudsonius)
Smelt, Rainbow (Osmerus mordax)
Snapper, Ruby (Etelis carbunculus)
Stoneroller, Central (Campostoma anomalum)
Sucker, White (Catostomus commersonii)
Swordfish (Xiphias gladius)
Threadfin, Sixfinger (Polydactylus sexfilis)
Trevally, Giant (Caranx ignobilis)
Tuna, Skipjack (Katsuwonus pelamis)
Tuna, Yellowfin (Neothunnus macropterus)
Whitefish, Lake (Coregonus clupeaformis)
Whitefish, Round (Prosopium cylindraceum)

Some shrimp, mussles, clams and other aquatic invertebrates have also been reported to contain thiaminase; see the Nutrient Requirements of Warmwater Fishes & Shellfishes by the NRC for more information.

The following fish have been reported free of thiaminase:

Amberjack, Greater (Seriola dumerilii)
Ayu (Plecoglossus altivelis)
Barracuda, Great (Sphyraena barracuda)
Bass, Largemouth (Micropterus salmoides)
Bass, Northern Rock (Ambloplites rupestris)
Bass, Northern Smallmouth (Micropterus dolomieu)
Bloater (Coregonus hoyi)
Bluegill (Lepomis macrochirus)
Cisco / Lake Herring (Coregonus artedi)
Cod, Atlantic (Gadus morhua)
Crappie, Black (Pomoxis nigromaculatus)
Croaker, Atlantic (Micropogonias undulates)
Croaker, Spot (Leiostomus xanthurus)
Cunner (Tautogolabrus adspersus
Dogfish, Piked (Squalus acanthias)
Eel, American (Anguilla rostrata)
Eel, Common (Anguilla anguilla)
Flounder, Winter / Lemon Sole (Pseudopleuronectes americanus)
Flounder, Yellowtail (Limanda ferruginea)
Gar, Longnose (Lepisosteus osseus)
Glasseye (Heteropriacanthus cruentatus)
Haddock (Melanogrammus aeglefinus)
Hairtail, Largehead (Trichiurus lepturus)
Hake (Urophycis)
Hake, Silver (Merluccius bilinearis)
Halibut, Atlantic (Hippoglossus hippoglossus)
Kawakawa (Euthynnus affinis)
Kingfish, Southern (Menticirrhus americanus)
Lizardfish, Inshore (Synodus foetens)
Mackerel, Atlantic (Scomber scombrus)
Marlin, Atlantic Blue (Makaira nigricans)
Mullet (Mugil)
Perch, European (Perca fluviatilis)
Perch, Ocean / Redfish (Sebastes marinus)
Perch, Yellow (Perca flavescens)
Pike, Northern (Esox lucius)
Plaice, American (Hippoglossoides platessoides)
Plaice, European (Pleuronectes platessa)
Pollock / Saithe (Pollachius)
Pumpkinseed (Lepomis gibbosus)
Salmon, Atlantic (Salmo salar)
Salmon, Coho (Oncorhynchus kisutch)
Scad, Mackerel (Decapterus pinnulatus)
Scad, Yellowtail (Atule mate)
Scup / Southern Porgy (Stenotomus chrysops)
Sea Catfish, Hardhead (Ariopsis felis)
Seabass, Black (Centropristis striata)
Searobin (Prionotus)
Seatrout, Sand (Cynoscion arenarius)
Seatrout, Silver (Cynoscion nothus)
Skate (Raja)
Smelt, Pond (Hypomesus olidus)
Soldierfish, Blotcheye (Myripristis berndti)
Sole, Common/Black (Solea solea)
Sprat, European (Sprattus sprattus)
Surgeonfish, Eyestripe (Acanthurus dussumieri)
Tautog / Blackfish (Tautoga onitis)
Tilapia (various species)
Trout, Brown (Salmo trutta)
Trout, Lake (Salvelinus namaycush)
Trout, Rainbow (Oncorhynchus mykiss)
Trout, Sea (Salmo trutta)
Tusk (Brosme brosme)
Walleye (Sander vitreus)
Weakfish, Sand (Cynoscion arenarius)

Please consult physicians/veterinarians, and/or other trustworthy science-based sources for advice on human and animal dietary questions.

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