thiaminase thiamin poisoning seafood fish carp trout salmon mussels krill shrimp cooked raw

What is Thiaminase poisoning?

Thiaminase is an enzyme found in various aquatic foods, including some fish, molluscs and crustaceans, many of which form the diets of turtles and other exotic pets in captivity. Fundamentally, Thiaminase breaks down and inactivates Thiamin (Vitamin B1), and if fed in large doses, or over a prolonged period of time, it can cause severe Vitamin B1 deficiencies, which are fatal if left untreated.

Vitamin B1 is essential for normal nervous system and immune system function, as well as generating energy (in the form of glucose) from carbohydrates in the diet. This means that animals which are fed a large amount of Thiaminase-containing foods and develop a Vitamin B1 deficiency often show symptoms of muscle and sensory disorders, susceptibility to disease and infection, and lethargy/lack of appetite.

How can Thiaminase poisoning be prevented?

In small, infrequent amounts, Thiaminase-containing foods cause only a low level of Vitamin B1 breakdown, and deficiencies in Vitamin B1 should not occur unless these foods form a regular part of a turtle's diet. Thiaminase, being an enzyme, is also destroyed by heat, and can be removed by cooking.

The easiest method of avoiding Thiaminase poisoning is to avoid Thiaminase-rich foods, and find suitable alternatives. Being aware of Thiaminase-rich foods, and making sure they are fed sparingly, or cooked beforehand, is a good idea, however the cooking process can reduce nutrition and make foods more difficult for exotic pets such as turtles to digest.

Thiaminase is not destroyed by freezing, and will continue to deplete the Vitamin B1 levels in frozen food over time. This is a particular problem with turtle and exotic pet species which are continually fed frozen/thawed fish, as if the frozen fish contains Thiaminase it will not only break up Vitamin B1 in the fish meat, but also break down any existing Vitamin B1 in the pet animal when consumed.

Which foods contain it?

The following live/fresh/frozen foods are known to contain Thiaminase, and should be avoided (*Please note this is not a comprehensive list, and is based mainly on readily-available foods):

  • Goldfish
  • Common Bream
  • Fathead Minnow / Rosy Red Minnow
  • Common Carp
  • Tunafish
  • Clams
  • Scallops
  • Mussels
  • Limpets
  • Prawns

  • In particular it is worth noting here that Goldfish and Fathead Minnows, sometimes recommended as "feeder fish", contain Thiaminase, and can contribute to Vitamin B1 deficiency.

    I continue to use Prawns and Mussels in the diets of my turtles, however these are available pre-cooked at most supermarkets.

    What are the alternatives?

    The following are readily available, Thiaminase-free foods:

  • Trout (Brown, Lake, Sea and Rainbow)
  • Salmon
  • Cod, Haddock and Pollock
  • Eel

  • Fresh Trout and Salmon are a good addition to the diets of many turtle species, and are readily available at supermarkets. Marine fish such as Cod can be fed, however I prefer to stick to freshwater fish meat for freshwater turtle diets.

    If you have any further questions regarding Thiaminase, or other turtle health issues, please email me:
    Paul Edmondson

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