Open a tin of tuna anywhere in the house and your cat materialises within seconds. It’s like a superpower. They can be dead asleep three rooms away and somehow the sound of a can opener brings them running. So the question isn’t whether your cat wants tuna — it’s whether you should actually give it to them.
The short version: a bit of tuna as an occasional treat is fine. Tuna as a regular part of their diet is a bad idea, for reasons that aren’t immediately obvious.
Why cats lose their minds over tuna
Cats are obligate carnivores. Their entire biology is wired around eating meat. Tuna specifically has a very strong smell and a high concentration of inosine monophosphate — a compound that hits feline taste receptors hard. It’s basically umami cranked up to eleven. Cats don’t taste sweetness (they lack the receptor), but they’re extremely sensitive to savoury and meaty flavours. Tuna maxes out that sense.
This is also why tuna can become almost addictive for some cats. Vets actually have a term for it: “tuna junkies.” These are cats who refuse to eat anything else after being given too much tuna, because everything else tastes bland by comparison. Getting a tuna junkie back onto regular food is a slow, frustrating process that usually involves mixing decreasing amounts of tuna into their meals over several weeks.
The mercury problem
This is the main reason tuna shouldn’t be a staple. Tuna is a large predatory fish that accumulates mercury through the food chain. The bigger and older the tuna, the more mercury it contains.
Cats are small animals. A 4kg cat eating tuna regularly is getting a proportionally much higher mercury dose than a 70kg human eating the same amount. Mercury accumulates in the body over time and can cause neurological problems: loss of coordination, tremors, vision issues. It doesn’t happen overnight — it’s a slow build-up over weeks or months of regular consumption.
Albacore (white) tuna has roughly three times more mercury than skipjack (light) tuna. If you do give your cat tuna, skipjack is the safer option.
What about cat food that contains tuna?
Commercial cat food with tuna as an ingredient is different from giving your cat human-grade tinned tuna. Cat food manufacturers formulate their products to be nutritionally complete — they add taurine, vitamins, and minerals that straight tuna doesn’t have. The tuna content is also controlled and balanced against other ingredients.
Human-grade tinned tuna is just… tuna. It’s protein and fat. It lacks taurine (which cats need for heart and eye function), has almost no calcium, and provides zero of the other micronutrients cats require. A cat living on plain tuna will develop serious nutritional deficiencies within months.
So: cat food with tuna flavour is fine as a regular food. Plain tinned tuna is a treat only.
How to give tuna safely
If your cat loves tuna, here’s the sensible approach.
Stick to once or twice a week at most. A tablespoon-sized portion is plenty. Choose tuna in water (springwater), not brine or oil. Brine has too much salt. Oil adds unnecessary calories and can cause digestive upset.
Fresh tuna — like sashimi-grade from a fishmonger — is actually the best option if you want to treat your cat. It’s lower in sodium than tinned, and you can control the portion more easily. Just make sure it’s fresh. Raw tuna sits in a grey area: some vets say it’s fine, others worry about bacteria and parasites. Lightly cooking it (seared, no seasoning) eliminates that risk.
Avoid tuna in any kind of sauce, dressing, or seasoning. Garlic and onion are toxic to cats, and these show up in some flavoured tuna products.
Signs you’re giving too much
If your cat starts refusing other food and only wants tuna, you’ve crossed the line into tuna-junkie territory. Scale back immediately. That’s the clearest signal.
Weight gain is another one. A whole tin of tuna has about 200 calories — which is most of a small cat’s daily requirement. If you’re adding tuna on top of their regular food, the calories add up fast.
Some cats also just don’t tolerate tuna well and get soft stools or diarrhoea. If that happens, tuna isn’t for your cat regardless of how much they want it.
Tuna water — the hack most cat owners don’t know
Here’s something useful: the water from a tin of tuna (plain, in springwater) is a great way to encourage cats to drink more. Pour a bit into their water bowl. Cats are notoriously bad at staying hydrated, and tuna water is usually enough to get them interested.
This works especially well for cats on dry food or cats with a history of urinary issues. You get the flavour appeal with minimal mercury risk, since most of the mercury stays in the flesh, not the water.
FAQ
Can kittens eat tuna?
In very small amounts, occasionally. Kittens need a nutritionally complete kitten food as their primary diet — their growth demands are high and tuna doesn’t cover them. A tiny taste once in a while won’t hurt, but it shouldn’t become a habit.
Is canned tuna better or worse than fresh for cats?
Fresh is better if you can get it. Lower sodium, no preservatives, and you can control the portion precisely. Canned in springwater is the next best option. Canned in brine or oil is the worst choice — too much salt or fat.
My cat only wants to eat tuna and refuses everything else. What do I do?
Classic tuna junkie. The fix is gradual: mix 75% tuna with 25% regular food for a few days. Then 50/50. Then 25/75. Then phase tuna out to a treat-only basis. It can take 2-3 weeks. Your cat will protest. Stay firm.
Is tuna-flavoured cat food safe for daily feeding?
Yes, if it’s a complete and balanced cat food (check the label for AAFCO or FEDIAF compliance). The tuna in commercial cat food is formulated to be safe for daily consumption. It’s the plain human-grade tuna that causes problems with daily feeding.
