by Richard Lunsford.

            Often on our forums people ask about, allude to or otherwise mention thiaminase, typically in discussions about fish in turtle diets, particularly frozen fish. Let’s talk about what it is, what it does, why it matters & what you should do about it. 

1.)    Thiamine is Vitamin B1 – a water-soluble vitamin involved in energy metabolism - much of what I know about it comes from its importance in thiamine deficiency in human alcoholics, but there’s a lot more to it than that. Click to read about it at (Note: I saw both ‘thiamine’ & ‘thiamin’ spellings used in online sources). 

2.)    Chronic, heavy drinking alcoholics may over-rely on alcoholic beverages as a caloric source & eat poorly, developing a thiamine deficiency over long periods. 

3.)    This can eventually lead to acute confusional episodes called Wernicke’s Encephalopathy. Click here to read about it.  

4.)    If this condition persists long enough, severely enough, it can lead to Korsakoff’s Psychosis (covered in the same link given for Wernicke’s Encephalopathy). K.P. is an anterograde amnestic state rather than a psychotic state. It can be permanent. 

5.)    This article at Cornell University states “In humans thiamin deficiency leads to a disease termed "beri-beri". Symptoms of beri-beri are basically the same as thiamin deficiency in other non-ruminants - anorexia, cardiac enlargement, and muscular weakness leading to ataxia. However, the disease has been divided into the following two forms:

                                                               i.      Dry beri-beri - usually without cardiac involvement, this form of the disease is typified by atrophy of the legs and peripheral neuritis. It occurs mainly in adults.

                                                             ii.      Wet beri-beri - the primary sign of this form of the disease is cardiac enlargement and edema.”

6.) In turtles, we turn to the Practical Encyclopedia of Keeping & Breeding Tortoises & Freshwater Turtles, Page 90, where A. C. Highfield states a Vitamin B deficiency (he doesn’t break it down, but B1 is clearly covered) can produce symptoms including muscle tremors, nervous type behavior and anorexia.

7.) Thiaminase (There are 2 types, Type I & Type II) is an enzyme.

8.)    Enzymes are biological catalysts made of proteins. 

9.)    A catalyst is a substance that speeds up a chemical reaction without being consumed by that reaction. It makes reactions happen faster. Like if a log rots over 5 years, & you somehow catalyze all the chemical reactions involved & make it rot in 5 minutes. 

10.)                        Our bodies require enzymes to speed some of the chemical reactions required in our metabolism. 

11.)                        Thiaminase destroys Thiamine (Vitamin B1). 

12.)                        Regular intake of substantial amounts of food containing thiaminase could introduce enough thiaminase into the gut to break down the thiamine in food & render an animal thiamine-deficient. 

13.)                        Some fish contain thiaminase (Type I, not II) & some don’t. 

14.)                        For an in-depth discussion of thiamine’s role in the body, Type I & Type II Thiaminase, check out this article at Cornell University

15.)                        Nutrient Requirements of Mink and Foxes, Second Revised Edition, 1982, Pages 64 & 65, provides tables of fish reported to contain & not to contain thiaminase. A sampling from those tables (bold emphasizing fish you might use): 

a.      Fish Reported to contain Thiaminase:

White Bass – Morone chrysops

Bowfin – Amia calva

Bream – Abramis brama (Not the U.S. fish; see this link).

Buffalofish – Ictiobus cyprinellus

Bullhead catfish Ameiurus m. melas

CarpCyprinus carpio

Channel Catfish Ictalurus punctatus

Fathead minnow Pimephales promelas (the red rosy is a color morph of this fish!)

Garfish (Garpike)

GoldfishCarassius auratus

Moray Eel – Gymnothorax ocellatus (since someone recently asked about keeping the brackish water species with turtles…)

Gizzard Shad Dorosoma cepedianum

Spottail ShinerNotropis hudsonius

Buckeye shiner Notropis atherinoides

Central Stoneroller – Campostoma anomalum pullum

Common White Sucker – Catostomus commersoni

Lake Whitefish – Coregonus clupeiformis


b.      Fish Reported to not contain Thiaminase:

Largemouth Bass – Huro salmoides (I think that’s actually now Micropterus salmoides)

Rock Bass – Ambloplites  rupestris

Smallmouth Bass Micropterus dolomieu

BluegillLepomis macrochirus

Chub (Bloater) – Coregonus hoyi

Cod – Gadus morhua

CrappiePomoxis nigromaculatus

Eel – Anguilla rostrata

Northern Longnose Gar – Lepisosteus osseus oxyurus

Northern Pike – Esox lucius

PumpkinseedLepomis gibbosus

SalmonSalmo salar

Brown Trout – Salmo trutta fario

Lake Trout – Salvelinus namaycush

Rainbow Trout – Salmo gairdnerii irideus


                        Note: Be aware that fish are acquired from pet stores, bait stores, traditional rod & reel or cane poll fish & netting (dip net, casting net, seine). So you may get such fish as shad… Since bluegill & pumpkinseed don’t contain thiaminase, I suspect the sunfish generally won’t (but that’s an assumption…). 

16.)                        It widely rumored that frozen fish is prone to contain more thiaminase than fish that has not been frozen. But why would this be so? Is it because thiaminase-containing fish are amongst species offered frozen, or because thiaminase is formed when some fish are frozen &/or thawed? 

17.)                        It makes no sense to me that something as complex as an enzyme would ‘accidentally happen’ (be made) when fish is frozen & thawed. However, if thiaminase were contained in the fishes’ cells, when those cells ruptured this might release thiaminase, making it easier to measure. I would expect digestion to rupture all the cells in a prey item, anyway. 

18.)                        However, in Practical Encyclopedia of Keeping & Breeding Tortoises & Freshwater Turtles, on Page 90 A. C. Highfield states that the enzyme thiaminase forms in fish after death. I have no idea where he got such info. & can neither prove nor disprove it. He also states that aquatic turtles with a diet including fish should always be provided a concurrent vitamin B1 supplement. 

19.)                        Thiaminase is of greatest concern to people feeding animals a fish-heavy diet, which while inappropriate for most species (i.e.: RES, stinkpots, etc…) may be needful in some (Chitra softshells & Mata Mata turtles). Occasional feedings should be irrelevant, but frequent feeding could in theory keep enough thiaminase in the gut to degrade thiamine. 

20.)                        Some Commercial Turtle Foods listing Thiamine on the label – ReptoMin®  (for aquatic turtles, newts & frogs), Wardley®  Reptile Sticks, Jurassi·Diet™ Aquatic Turtle Food, Jurassi·Diet™ Reptile Food, Nature Zone Aquatic Turtle Bites, T-Rex®  Tortoise Dry Formula, Mazuri® Fresh Water Turtle Diet, Mazuri® Tortoise Diet.


21.)                        Options to combat thiaminase deficiencies include: 

a.       Oral supplementation of thiamine – I ‘m not up on this. Most won’t need to explore it but if you keep a Mata Mata, Chitra softshell or other animal with a high-fish (in some cases only fish) diet you’d better look into it.

b.      Avoiding fish known to contain thiaminase – no red rosies or feeder goldfish! And who knows whether guppies or platys contain it or not?

c.       Don’t feed fish over once per week on an ongoing basis – ensuring the turtle eats nutritious food likely to contain thiamine (like reputable commercial turtle foods) when they’ve had no fish for a few days should help ensure the body gets to absorb thiamine.

d.      Heat that Cornell article points out that “Thiaminases are denatured by heat, therefore subjecting any of the sources of thiaminases to cooking or other heat treatment will render the thiaminases inactive.” Unfortunately, it doesn’t tell us how much or how long to heat it. Perhaps slow baking or broiling? In this case ‘denature’ refers to the breakdown of a protein under heat.’s entry includes a number of definitions of ‘Denature,’ including “To cause the tertiary structure of (a protein) to unfold, as with heat, alkali, or acid, so that some of its original properties, especially its biological activity, are diminished or eliminated.”


Appendix of Useful Online Resources: 

I.)       ’s Thiamine Info. Page.

II.)               Cornell University’s Thiaminase Article.

III.)            Fish Base – an online relational database global info. system on fish claiming to have 28500 Species, 193900 Common names, 36700 Pictures, 33700 References, 1110 Collaborators & 11 million Hits/month. Their search page is useful to pulling up info. on wild fish species.

IV.)   – self-explanatory.