Can Cats Eat Tuna? What You Must Know

Reviewed by Dr. Ameer Hamza, DVM

Cats and tuna have a reputation that has become somewhat misleading. Yes, cats love tuna. Yes, a small amount occasionally is fine. But the relationship between cats and tuna is much more complicated than popular culture suggests — regular tuna feeding causes real problems that accumulate gradually and are not always obvious until they become serious. Here is what you actually need to know.

Is Tuna Safe for Cats?

Tuna is not toxic to cats in the way that onions, grapes, or xylitol are. A small piece of tuna or a lick of tuna-flavoured water will not harm your cat. The issue is not acute toxicity but chronic damage from regular feeding. Tuna consumed occasionally as a treat is acceptable for most healthy adult cats. Tuna consumed regularly — several times a week or as a meal replacement — creates three distinct problems: mercury accumulation, thiamine deficiency (from raw preparations), and nutritional incompleteness.

The Mercury Problem

Tuna is among the higher-mercury fish available. Mercury accumulates in body tissue over time through a process called bioaccumulation — each tuna your cat eats has itself accumulated mercury from its own diet, and that mercury is transferred to your cat. In small amounts this is not a problem; the kidneys and liver process and excrete a certain amount of mercury effectively. The issue arises with regular, ongoing consumption where the intake rate exceeds the excretion rate.

Cats fed tuna regularly over months or years can develop mercury toxicity, which manifests as neurological symptoms: difficulty walking, loss of balance and coordination, tremors, and impaired vision. These symptoms develop slowly and may not be immediately linked to diet without a full history. Because cats are small, their toxic threshold is reached at lower absolute doses than in humans.

Light canned tuna — from skipjack — contains significantly less mercury than albacore or bluefin tuna. If you do offer tuna as an occasional treat, light canned tuna in spring water with no added salt or flavouring is the most reasonable choice.

Thiamine Deficiency and Raw Tuna

Raw tuna and some other raw fish contain an enzyme called thiaminase, which destroys thiamine (vitamin B1) in the digestive tract. Thiamine is essential for nervous system function in cats. A cat whose diet is regularly supplemented with raw tuna can develop thiamine deficiency even if they are eating a complete commercial cat food alongside it, because the thiaminase from the raw fish depletes thiamine from the whole meal.

Signs of thiamine deficiency in cats include loss of appetite, vomiting, abnormal posture (ventroflexion — the neck bending down), seizures, and in severe cases, coma. This is a serious and progressive condition that requires veterinary intervention. Cooked tuna does not carry this risk because heat deactivates thiaminase. Commercially canned tuna is cooked during processing, so canned tuna does not cause thiamine depletion. Raw tuna from a fishmonger or sushi-grade tuna offered as a treat is the higher-risk form.

Nutritional Incompleteness

Cats are obligate carnivores with highly specific nutritional requirements. Unlike commercial cat food, which is formulated to meet AAFCO nutritional profiles, plain tuna is not a complete food for cats. It lacks adequate taurine (though it contains some), vitamin E, several B vitamins, calcium, and other nutrients that cats need in precise amounts. A cat eating tuna as a significant portion of its diet — rather than as an occasional treat — will develop nutritional deficiencies over time regardless of the mercury question.

Some cats fed tuna regularly also develop what veterinary nutritionists call "tuna addiction" — a strong preference for tuna so intense that they refuse to eat their complete cat food. This creates a situation where owners feel pressured to keep feeding tuna to prevent their cat from going hungry, which worsens the nutritional imbalance. The solution is prevention: keep tuna occasional from the start and do not allow it to become a meal staple.

How Much Tuna Is Safe for Cats?

If you want to offer tuna as an occasional treat, the general guideline is a teaspoon-sized amount no more than once or twice a week, mixed into or offered alongside their regular complete cat food. This is sufficient to satisfy the cat's interest without approaching the levels that cause mercury accumulation or nutritional disruption. For smaller cats, adjust down proportionally. For cats with kidney disease, hyperthyroidism, or other health conditions, discuss any dietary addition with your vet before offering it.

Which Type of Tuna Is Best for Cats?

If you are going to offer tuna, canned tuna in spring water is the most appropriate option. Avoid tuna in oil (adds unnecessary fat and calories), tuna in brine (high sodium, which strains the kidneys), and flavoured varieties. Check the ingredient list for any additives. For the mercury question, light tuna (skipjack) is preferable to albacore or yellowfin. Do not offer raw tuna regularly due to the thiaminase issue.

Tuna-Flavoured Cat Food vs Actual Tuna

Tuna-flavoured commercial cat foods are formulated to be nutritionally complete and are manufactured to meet AAFCO standards. They are not the same as feeding plain tuna. These foods use processed tuna ingredients at controlled levels, are fortified to correct the nutritional gaps in plain tuna, and use preparation methods that eliminate the thiaminase concern. A cat eating a high-quality tuna-flavoured complete wet food is in a very different nutritional situation from a cat eating plain canned tuna regularly.

Frequently Asked Questions

Can cats eat tuna every day?

No. Daily tuna feeding leads to mercury accumulation, potential thiamine deficiency from raw forms, and nutritional imbalance because plain tuna is not a complete food for cats. Some cats fed tuna daily also develop such a strong preference for it that they refuse their complete cat food. Once or twice a week in small amounts is the maximum reasonable frequency for healthy adult cats.

Is tuna in spring water better than tuna in oil?

Yes. Tuna in spring water is the best option for cats because it adds the least additional fat and sodium. Tuna in oil is higher in fat and calories, which adds up quickly given cats' small size. Tuna in brine contains significant salt, which places extra strain on cats' kidneys. Always check the label for added flavourings or preservatives, even in products marketed as plain tuna.

Can cats eat raw tuna?

Raw tuna should not be offered regularly. It contains thiaminase, an enzyme that destroys thiamine in the digestive tract. Thiamine deficiency causes serious neurological symptoms in cats, and the condition develops progressively with ongoing raw fish consumption. Commercially canned tuna is cooked during processing and does not carry this risk. If you want to offer tuna occasionally, canned light tuna in spring water is a safer choice than raw.

Why does my cat love tuna so much?

Cats are biologically wired to seek out protein-rich, fat-rich food sources, and tuna has an exceptionally strong scent and flavour profile that appeals to their highly developed sense of smell. The attraction is driven by the same instincts that make cats effective hunters. The risk is that this preference can become reinforced into a habit that makes other foods seem unpalatable by comparison, which is why keeping tuna occasional matters even if your cat would happily eat it at every meal.

What is mercury poisoning in cats?

Mercury toxicity in cats accumulates over time through regular consumption of high-mercury fish. It presents as loss of balance and coordination, tremors, difficulty walking, and impaired vision — symptoms that develop gradually and may initially be attributed to other causes. If your cat has been eating tuna regularly and shows these signs, inform your vet about the diet history. Removing tuna from the diet and supporting kidney function are the primary interventions.

For a broader picture of what cats can and cannot safely eat, the guides to chicken for cats and cheese for cats cover two other common questions in full. For a complete overview of feline nutrition, the cat care hub is a good starting point.

---

Disclaimer: This article is for educational purposes only. Always consult your veterinarian before introducing new foods into your cat's diet, especially if your cat has existing health conditions.