Kitty That Only Wants Fish

Answers: Kitty That Only Wants Fish

My cat only wants to eat fish! Can I feed her a diet that is mostly fish or should I try to limit how often I feed it?
Fish contains thiaminase, an enzyme that will destroy thiamine, which is vitamin B1. Thiamine deficiency causes severe neurological symptoms and can be fatal. Cats have a high requirement for B vitamins - a continual dietary source is required to prevent deficiency. Deficiency is very rare in cats consuming their natural diet, as B vitamins are plentiful in animal tissues. A cat would have to eat fish at every meal for a long time to develop a deficiency. I recommend cats consume fish up to three times a week. Variety is the key when feeding a raw diet and I would encourage the feeding of any particular food up to three times a week but no more.
Be careful if feeding meat-only products - including fish or shellfish - that have been preserved with a sulphur-based preservative. These sulphur-based preservatives inhibit thiamine absorption. These preservatives "hold" the colour of the meat for an unnaturally long time so they stay looking good in the fridge. The preservatives can also trigger asthma in cats.¹ Products marketed for pets, e.g. commercial fresh "pet meat," "pet mince" or processed/manufactured "pet food rolls," may contain sulphite preservatives, so check the labels carefully. Thiamine deficiency can occur when cats and dogs are fed on a diet containing sulphite preservatives.²
The fatty acids in oily fish are very beneficial for cats and dogs, particularly those with chronic inflammatory health issues, and it is a good idea to include oily fish in the diet 2-3 times per week. Tinned tuna is not the greatest source of fatty acids. Sardines canned in water are a much better source. They are also less likely to pose a heavy metal risk than top-of-the-food-chain fish such as tuna.
If you are feeding fresh-caught fish, then you should freeze the fish to an internal temperature of -20°C (-4°F) for at least seven days to kill any parasites that may be present. Home freezers are usually between -17°C and -12°C (0°F and 10°F) and may not be cold enough. Commercially caught fish is almost always frozen during transport and processing to temperatures low enough to kill any parasites present.
Note: Feline Nutrition provides feline health and nutrition information as a public service. Diagnosis and treatment of specific conditions should always be in consultation with your own veterinarian. Feline Nutrition disclaims all warranties and liability related to the veterinary advice and information provided on this site.
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Dr. Lyn Thomson trained at the University of Bristol in England and is studying with the Australasian College of Nutritional and Environmental Medicine. A dedicated and experienced advocate of bio-appropriate nutrition, Lyn practices in Auckland, New Zealand. Her Raw Essentials stores have grown to seven retail locations, providing a variety of raw diet products for cats and dogs.
  1. BJ Freedman, "Sulphur Dioxide in Foods and Beverages: Its Use as a Preservative and its Effect on Asthma," British Journal of Diseases of the Chest 74, no. 2, April 1980, 128-34.
  2. R Malik and D Sibraa, "Thiamine Deficiency Due to Sulphur Dioxide Preservative in 'Pet Meat' – a Case of Déjà Vu," Australian Veterinary Journal 83, no. 7, July 2005, 408-11.
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