Can My Cat Eat Tuna? What you need to know first

This article is based on veterinary guidance from UK and international animal health organisations including Cats Protection, Applaws UK, and SHEBA UK.

Open a tin of tuna anywhere in the house and your cat will appear from nowhere. It's one of those universal cat truths. But just because cats love something doesn't mean it's good for them, and tuna sits in an interesting middle ground: not toxic, but not without risk either.

This guide covers exactly what you need to know: the benefits, the real risks, how much is safe, which types to avoid, and what signs to watch for if your cat has had too much.

Related: See our full guide to what cats can and can't eat, and our toxic plant guide for cat owners.

Is tuna safe for cats?

Yes…in moderation. Tuna is not on any veterinary toxic foods list for cats, and a small amount as an occasional treat is unlikely to cause harm. In fact it has some genuine nutritional benefits.

Cats Protection, the UK's largest cat welfare charity, confirms that a small amount of tuna is unlikely to cause harm, but recommends it is not fed regularly due to the lack of essential nutrients cats need for optimal health.

The benefits

• High protein, low carbohydrate - cats are obligate carnivores and thrive on protein-rich food. Tuna fits that profile well.
• Rich in omega-3 fatty acids - supports a healthy coat, skin, and cardiovascular health.
• Highly palatable - useful for getting reluctant cats to take medication or eat when they're off their food.
• Low in carbohydrates - cats lack the enzyme needed to efficiently process dietary carbohydrates, so low-carb foods suit them well.

The risks of feeding cats too much tuna

This is where it gets important. Tuna is fine as a treat, it's problematic as a regular food. Here's why:

1. Mercury accumulation

Tuna is a large predatory fish, which means it sits high on the food chain and accumulates mercury. According to veterinary nutritionists at the Cummings School of Veterinary Medicine at Tufts University, frequent tuna consumption can lead to mercury build-up in cats over time.

Albacore (white) tuna carries significantly higher mercury levels than chunk light tuna, roughly three times higher, so if you do feed tuna, chunk light is the safer choice.

Signs of mercury poisoning in cats include loss of coordination, tremors, muscle weakness, and in severe cases, seizures. If you notice any of these symptoms, contact your vet immediately.

2. Nutritional imbalance

Applaws UK notes that tuna lacks several nutrients that cats need, including taurine, vitamin E, and calcium. Taurine in particular is critical, cats cannot produce it themselves and a deficiency causes serious heart and eye problems.

Human-grade tuna is also deficient in vitamin E, which can cause steatitis (a painful inflammation of body fat) when fed in large amounts over time. Cat-specific tuna products are supplemented to address this, which is why they're a safer option than supermarket tins.

3. High calorie content

A small tin of tuna in water contains around 100 calories, more than a third of the daily calorie requirement for an average adult cat. Fed on top of regular meals, it can quickly lead to weight gain, and with that comes increased risk of diabetes, arthritis, and urinary disease.

4. Addiction and fussy eating

Your Vet Online warns that some cats become so fond of tuna that they start refusing their regular complete food. This is a real problem, a cat that only eats tuna is a cat that's nutritionally deficient. If your cat starts turning their nose up at normal food after getting tuna, scale it back immediately.

5. Thiamine deficiency (mainly raw tuna)

Raw tuna contains thiaminase, an enzyme that destroys thiamine (vitamin B1). Cooking destroys thiaminase, so canned tuna doesn't carry this risk in the same way. But it's worth knowing that raw tuna fed regularly can cause thiamine deficiency, with symptoms including poor coordination, neck bending, and seizures.

Which type of tuna is safe?

Source: Perfect Fit UK, SHEBA UK, Applaws UK

How much tuna can cats eat?

The key principle, as agreed across UK and international veterinary sources, is: treat it like a treat. Here's a rough guide based on body weight:

These are maximum guidelines - less is perfectly fine. The goal is to keep tuna as a small supplement to a complete balanced diet, not a meal in itself.

Important: Kittens under one year old should not be given tuna. They are more sensitive to nutritional imbalances and to toxins including mercury, and their growing bodies need the precise nutrition of a complete kitten food.

Signs your cat has had too much tuna

If your cat has eaten a larger amount of tuna than recommended, most cases result in mild gastrointestinal upset at most. But watch for these signs and contact your vet if you're concerned:

Short-term (after a large amount in one sitting)

• Vomiting or diarrhoea
• Loss of appetite
• Lethargy

Long-term (from regular excessive feeding)

• Weight gain and obesity
• Refusing regular cat food
• Loss of coordination or balance (mercury)
• Muscle tremors or weakness (mercury)
• Neck bending downward (thiamine deficiency - more likely from raw fish)
• Coat becoming dull or patchy (vitamin E deficiency)

Cat-specific tuna vs. supermarket tuna - is there a difference?

Yes, and it matters. Tuna made specifically for cats (cat food labelled as complete or complementary) is formulated differently to supermarket tuna:

• Complete cat tuna food - contains added taurine, vitamins, and minerals to make it nutritionally balanced. Can be fed as a regular meal.
• Complementary cat tuna - better than supermarket tuna but not nutritionally complete on its own. Should be fed alongside complete food.
• Supermarket tuna (human grade) - lacking in key nutrients, higher sodium, no added taurine. Treat only, once a week maximum.

If you want to include tuna regularly in your cat's diet, a complete cat food that uses tuna as its protein source is far safer than opening a tin from the cupboard.

The short version

• Yes, cats can eat tuna - but only plain tuna in spring water, as a treat, once a week at most.
• Never feed tuna in brine, oil, or with seasonings - these can cause real harm.
• Tuna is not nutritionally complete - it should supplement a balanced diet, never replace it.
• Kittens should not eat tuna - wait until they're at least one year old.
• Watch for signs of overfeeding - particularly fussy eating and weight gain.
• Cat-specific tuna products are safer - they're formulated with the nutrients supermarket tuna lacks.

When in doubt, ask your vet - especially if your cat has kidney disease, is overweight, or is elderly, as tuna may not be appropriate for them at all.

Frequently asked questions

Can cats eat tuna every day?

No. Daily tuna feeding risks mercury build-up over time and will almost certainly cause nutritional deficiencies. Once a week is the maximum recommended by vets, and less is fine.

Can cats eat tuna in brine?

No, tuna in brine contains high levels of sodium which can cause dehydration and electrolyte imbalance in cats. Always choose tuna in spring water if you're going to offer it at all.

Can kittens eat tuna?

No. Vets recommend waiting until cats are at least one year old before offering tuna. Kittens are more sensitive to nutritional imbalances and to mercury exposure.

My cat only wants to eat tuna - what do I do?

This is a common problem. Gradually reduce the amount of tuna and mix a tiny amount into their regular complete food to re-introduce it. If they've gone completely off their normal food for more than 24 hours, speak to your vet.

Can cats with kidney disease eat tuna?

Tuna is high in phosphorus, which can strain kidney function in cats that already have kidney disease. If your cat has been diagnosed with kidney disease, check with your vet before offering any tuna at all.

Is tinned tuna in spring water really safe?

Yes, in small amounts once a week. Check the label carefully, some spring water tuna still contains added salt. Choose one with no added salt, seasonings, or additives. Brands that mercury-test their tuna are a safer choice where available.