Can Cats Eat Tuna? What Vets Say About Mercury, Thiamine, and Safe Amounts

Open a can of tuna and most cats appear out of nowhere. That reaction alone convinces a lot of owners that tuna must be some kind of ideal cat food. It isn't, and the reasons why are more specific than "too much of anything is bad." Tuna fed regularly can cause two distinct, well-documented problems in cats, and both are avoidable once you know what's actually happening.

Is tuna safe for cats at all?

In small, occasional amounts, yes. A bite of plain, cooked, unseasoned tuna as a treat isn't dangerous for a healthy adult cat. The trouble starts when tuna becomes a regular part of the diet rather than an occasional taste, which is easy to slide into given how much cats seem to want it.

The mercury problem

Tuna, especially albacore, accumulates more mercury than most fish because it's a larger, longer-lived predator species higher up the food chain. PetMD notes that a cat fed tuna heavily over time can build up enough mercury to cause toxicity, with symptoms including muscle weakness, tremors, and in severe cases seizures. A cat's small body size means the same portion that's negligible for a person represents a much larger dose relative to their weight.

Thiamine deficiency and steatitis

Raw fish contains an enzyme called thiaminase that breaks down thiamine (vitamin B1) before the body can use it. Cooking destroys thiaminase, which is one reason canned tuna is safer than raw fish, but veterinary nutritionists point out that a fish-heavy diet can still run low on thiamine over time, and a deficiency shows up as poor appetite, wobbliness, and in advanced cases seizures.

Separately, tuna is high in unsaturated fat and low in vitamin E. A cat fed a tuna-heavy diet for weeks can develop steatitis, also called yellow fat disease, a painful inflammation of body fat caused by that fat oxidizing faster than the cat's vitamin E can protect it. This isn't a new or rare finding: it was first documented in cats fed canned red tuna back in a 1958 case series in the Journal of the American Veterinary Medical Association, and vets still see it today. A 2022 case report on a young cat with pansteatitis is a reminder that this isn't only a problem from decades ago.

What about tuna-flavored cat food?

Tuna-flavored commercial cat food is a different product from a can of human tuna. It's formulated to be nutritionally complete, with taurine, vitamin E, and thiamine added back in, and it's usually a blend of ingredients rather than straight tuna. Feeding tuna-flavored cat food as a cat's regular diet doesn't carry the same steatitis or thiamine risk that feeding human tuna as a meal replacement does.

How much tuna is actually safe?

A small amount of plain, cooked tuna, roughly a tablespoon, once a week or less, is unlikely to cause problems in an otherwise healthy cat eating a complete diet the rest of the time. Tuna packed for humans (especially in oil) shouldn't become a daily habit or a meal replacement. If your cat seems to prefer tuna over their regular food to the point of refusing meals without it, that pattern is worth mentioning to a vet, since selective eating can also mask an unrelated health issue. For a broader rundown of what's genuinely risky in the kitchen, see our guide to which human foods are toxic to cats.

Frequently asked questions

Can kittens eat tuna?
It's best avoided. Kittens have higher nutritional needs relative to their size, and a food that displaces balanced kitten food, even occasionally, is a bigger risk for them than for an adult cat.

Is canned tuna in water safer than tuna in oil?
Yes, tuna packed in water has less added fat, which matters if you're worried about steatitis risk from frequent feeding. Neither changes the mercury content.

My cat only wants to eat tuna. Is that a problem?
It can turn into one. Cats can develop a strong preference for tuna's taste and smell and start refusing balanced food in favor of it, which is exactly the pattern that leads to thiamine deficiency and steatitis over time. It's worth breaking the habit early.

Sources

• PetMD, "Can Cats Eat Tuna?"
• Nutrition RVN, "Thiamine Deficiency & Fish"
• Munson, T.O. et al., "Steatitis (yellow fat) in cats fed canned red tuna," Journal of the American Veterinary Medical Association, 133 (1958): 563-568
• Research in Veterinary Science and Medicine, "Pathological Findings of Feline Pansteatitis in a 9-Month-Old Siberian Queen"
• Catster, "Can Cats Eat Tuna? Vet-Reviewed Nutrition Facts & FAQ"

This article is for general information and isn't a substitute for advice from your own veterinarian, who can evaluate your cat's specific diet and health history.