Can cats eat tuna?

So there I was at 2 a.m., holding a frantic tortoiseshell cat named Patchhes while she shook and drooled on my sweatshirt, and all I could think was: I gave her tuna. I'm the biggest idiot on this entire block.

This was 2015. I'd been fostering for maybe three years at that point — long enough to know better, but still green enough to pull stuipd moves like thinking a little tuna water was a nice treat. Patches had come in from a hoarding situation, barely eating, and I just wanted her to get some calories. So I opened a can of albacore, drained the juice into her bowl, and watched her lap it up like a tiny, starving athlete.

She loved me for it. For about eight hours. Then her nervous system started shorting out and I spent the worst night of that year sitting on the floor of an emergency vet clinic wiping tuna-scented vomit off my jeans.

I'm Sarah. I've fostered 40-plus cats, made every mistake there's, and I'm still mad that nobody tells you the simple stuff when you start. So here's the truth about cats and tuna — the messy, unsanitized veersion that doesn't come on a cat food label.

The first time I gave a cat tuna, I thought I was being nice

I was 19 and living in a terrible studio apartment with my first cat, a gray shorthair named Mooch. Mooch was a garbage disposal with whiskers. He once ate an entire stick of butter off the counter while I was in the shower. So when I opened a can of tuna for my own sandwich and he came running, I figured: sure, why not? It's fish. Cats eat fish. The cartoons told me cats and tuna are basically married.

I gave him a little flake. Then another. Then maybe a tablespoon because he was screaming like I'd never fed him a day in his life. He was fine the next day. No shakes, no vomit, just a cat who had discovered a new religion and now followed me around every time I touched a can opener. I thought I was a genius. Look at me, bonding with my cat through food.

And that's the trap. Most cats will eat tuna. Most won't drop dead from one tiny taste. So people keep doing it. Then keep doing it. Then one day they're at the vet with a cat who's lost weight, is throwing up foam, and has a weird twitch in her back legs and nobody connects it to the can of StarKist they've been splitting with her every Sunday for two years.

I know because I've been that person. Twice. Patches was the second time. The first time was a build named Lenny who I'll talk about in a minute. Let me say this now so we're clear: tuna isn't poison in one bite, but the way we — normal, well-meaning peoole — tend to feed it? That's where the problems live.

I'm not a vet. Dr. Nguyen, who's put up with my panic calls since 2009, once told me, 'Sarah, if you bring me one more cat with fish-induced problems, I'm going to start charging you a tuna tax.' She was joking. Mostly.

Wait — tuna's in cat food all the time. So why is my vet giving me the side-eye?

This is the question I get every damn time I tell adopters to skip the tuna. And I get it. You walk down the cat food aisle and half the cans have 'tuna' on them. There's tuna and shrimp, tuna and whitefish, tuna fillet in gravy that looks better than my own lunch. So if it's safe enough for commercial cat food, why am I being a paranoid weirdo about the stuff from your pantry?

The short answer: because the tuna in cat food is processed differently, it's part of a balanced formulation, and — this is the big one — it's not the same as human-grade canned tuna. Pet food manufacturers have to meet AAFCO standards for nutrition. Your can of Bumble Bee doesn't. More importantly, they're required to monitor for contaminats (yes, including heavy metals) and they use parts of the fish that aren't the high-mercury steaks. There's a whole world of fish processing that no one talks about unless you're stuck in a rabbit hole at 3 a.m. with a cat who won't eat.

But here's the thing that really bugs me: just because something is in cat food doesn't mean it should be the only thing you feed. I've got a whole rant about that. I adopted a cat back in 2018, a senior tabby named Ollie, who'd been eating nothing but tuna-based wet food for three years because his previous owner thought 'he likes it' was a good enough reason. Ollie came to me with inflamed gums, a weird gait, and phosphorus levels that made Dr. Nguyen go 'hmm' in that way vets do when they're trying not to alarm you. It turned out his diet was so out of whack — tons of fish, no variety — that he was borderline thiamine deficient and his kidneys were stressed. And this was from actual cat food, not even human tuna.

Which brings me back to the point: human tuna is even less balanced. It's like eating nothing but fench fries and calling it 'potato nutrition.' The potato's in there, sure, but you're missing everything else and you're getting way too much salt and oil and whatever else is in the can.

Speaking of missing everything else — I once spent three years chasing 'natural' fixes for feline health problems, convinced I could outsmart commercial pet food with homemade diets. I failed so spectaculrly that my vet did an intervention. I wrote about that whole disaster over here, along with the three things that actually made a difference. But the tuna part is relevant: I thought if it was 'natural,' it was fine. Turns out natural also includes mercury.

Mercury poisoning sounds like somethng that happens to whales, not your 10-pound tabby

So let's talk about mercury. I'm going to need to back up a second because I just realized I've been throwing that word around like everyone knows what it means. I didn't know, not really, until Lenny almost died.

Lenny was a flame-point Siamese mix I fostered in 2013. He came to me skin and bones, and I was determined to fatten him up. I started giving him a little tuna every day — just a teaspoon mixed into his regular food, because I read online that it 'enticed picky eaters.' I did this for about six weks. He gained weight, his coat got glossy, everything looked great. Then one morning he stumbled off the couch and fell on his face. He couldn't walk straight. His pupils were two different sizes. I lost my mind.

The emergency vet did bloodwork. Nothing obvious. Then they did a heavvy metal panel — and his mercury levels came back high. I'm not talking 'a little elevated' — I mean high high, like 'this cat has been eating ocean predator for decades' high. Except he was three years old and had only been with me for six weeks. When I told the vet about the daily tuna, she closed her eyes for a long time before answering. I'll never forget that look.

Here's why that happened. Tuna — especially albacore and bigeye tuna, which are the ones in the larger, 'solid white' cans — are top predators. They eat smaller fish. Those smaller fish eat smaller fish. Every step up the food chain, mercury from pollution gets concrntrated. It's called bioaccumulation. A 10-pound cat eating just a teaspoon of albacore tuna every day is getting way more mercury per pound of body weight than a 200-pound human eating a whole tuna sandwich.

And mercury is nasty. It's a neurotoxin. In cats, chronic low-level exposure can cause ataxia (the stumbling thing), tremors, vision problems, kidney damage, and weird behavioral changes that you might just chalk up to 'getting old.' I've seen it twice now, and both times I missed the early signs because they're subtle: a slight wobble on the cat tree, a little more sleeping, a little less appetite. By the time they're falling over, the damage might already be permanent.

How much tuna is 'too much'? (The answer made me want to throw all my cans away)

Dr. Nguyen once gave me a rule of thumb that I've never forgotten: for an average 10-pound cat, anything more than half a teaspoon of albacore tuna once a week puts them at risk over time. Light tuna (like skipjack) has less mercury, so you could theoretically do a full teaspoon a week, but that's still pushing it. Those numbers are for occasional treating, not daily feeding. If you're usong tuna every day to get your cat to eat — stop. There are better ways, and I've got a whole post about what finally worked for my picky fosters right here.

But the thing is, nobody measures out half a teaspoon. I sure didn't. I'd spoon out a 'little bit' and then Lenny would scream so I'd give him 'just a little more' and before I knew it he'd eaten the equivalent of a whole can over a few days. So the real answer? Unless you're the kind of person who weighs your ca'ts treats on a kitchen scale (and if you're, respect), you're probably better off avoiding tuna entirely.

What mercury toxicity actually looked like in my own house

Patches — the tortie from the intro — was the second cat I poisoned with my 'kindness.' I thought I'd learned my lesson after Lenny. But Patches wasn't getting tuna daily; she got tuna juice just twice in three days, and then a few flakes on the fourth day because I'm an idiot who thought juice was safer than meat. It wasn't.

She started with hyper-salivation (like a waterfall of drool), then progressed to rapid eye movement that looked like she was tracking invisible bugs. By the time we got to the vet, she had mild tremors and couldn't keep her balance. Her mercury levels weren't as off-the-charts as Lenny's, but combined with her already frail body from the hoarding situation, it was enough to tip her over.

She recovered — slowly, with fluids and chelation and a lot of expensive vet visits. I think the total bill for Patches was around $1,100. For tuna juice. I could've boought 400 cans of actual cat food for that money. Or, you know, zero cans of tuna.

This is where I'm supposed to write a smooth transition to the next point about salt and oil, but I'm honestly still mad about Patches, so here's a new heading instead.

And then there's the salt bomb and the oil slick nobody talks about

Mercury gets all the scary headlines, but the everyday problens with tuna are almost worse because they fly under the radar. Most canned tuna for humans is packed in either brine (salt water) or oil. Both are bad for cats. Like, really bad.

The brine tuna is a sodium nightmare. A single teaspoon of brine-packed tuna can have 40-50 mg of sodium. For a 10-pound cat, that's a significant hit. Cats with even mild kidney issues — and a shocking number of cats over 7 have undiagnosed renal insufficiency — can get knocked off balance fast. I had a senior build named Beatrice who went into acute kidney failure after her new adopter fed her 'just a little' salty tuna for a week. Beatrice survived, but her kidneys never fully bounced back. I had to help that family learn all about subcutaneous fluids. You don't want to be the person who learns about subcutaneous fluids because you offered a treat.

Oil-packed tuna is a different can of worms. That oil is usually soybean or olive oil, and while olive oil isn't toxic, the sheer fat content can trigger pancreatitis in sensitive cats. Pancreatitis is one of those things that sounds manageable but in reality means your cat stops eating, starts hiding, and needs to be hospitalized on IV fluods and pain meds for days. I saw a build kitten get pancreatitis from a few licks of tuna oil; it was a $700 lesson.

And then there's the histamine thing, which I learned about after a particularly bad night with a cat who ate tuna that had been open in the fridge for three days. Tuna — even properly stored — can develop high histamine levels that cause something called scombroid poisoning. The cat was fine eventually, but for a few hours I thought I was watching another Patches repeat. The vet told me that's rare but possible, and honestly, even a 0.1% chance of a cat experiencing that from a treat is too much for me.

I walked into the shelter's break room and found a volunteer feeding tuna juice to three kittens

This isn't really a tangent because it's about tuna, but I'm pitting it here because it makes me want to pull my hair out. A couple years ago, I was at the shelter where I used to work, picking up a transport of kittens, and I walked into the break room to see a well-meaning volunteer spooning the liquid from a can of chunk light tuna into a dish for three 6-week-old kittens. I think I actually said, 'Oh, no. Oh, no no no.'

She looked up at me with this big smile, like she'd found the secret to making kittens happy, and I had to do that thing where you're gentle because the person means well but you also want to scream. I explained everything — the mercury, the salt, the fact that kittens this age have developing nervous systems and are even more vulnerable — and she lopked genuinely horrified. She'd been doing it for two days. Thankfully, all three kittens were fine. But the whole thing stuck with me because this is how it happens. Good people, doing what seems like a good thing, with zero information.

The shelter put up a sign after that. It said, 'No tuna, please. Even if you think it's just a treat.' I still think about that sign. It saved some cats, probably.

Anyway, that same year I had a build cat named Mr. Bubbles who was the pickiest eater on the planet, and I was desperate enough to try EVERYTHING. I learned then that there are entrees and broths that mimic tuna but are actually safe. That whole saga is in my post about cat food that finally stopped the carpet cleanups — check it out if you've a cat with a sensitive stomach. But the point here's: the impulse to sahre tuna isn't evil, it's just uninformed. And I was there once too.

The time I gave a kitten tuna juice and everything was fine (for three dys, then everything was very much not fine)

Okay, this is the third tuna story in this article and you're probably thinking, 'Sarah, how many times did you poison cats with tuna before you stopped?' The answer is: more than I care to admit. But this one is particularly memorable because it involves a kitten named Fig. Fig was a 5-week-old bottle baby I took in after his mom was hit by a car. He was doing great for about a week, then suddenly stopped gaining weight. He wasn't interested in his formula. I panicked and adedd a few drops of tuna water to entice him — something I'd done successfully with older cats, and yes I know I should've known better but sleep deprivation makes you stupid.

He loved it. Gobbled his whole bottle. I did it again the next feeding. And the next. For three days, Fig was a new kitten: energetic, gaining, eyes bright. I was so proud of myself for figuring it out.

Then he started vomiting. Not just a little spit-up — projectile vomiting that made me think he'd swallowed something he shouldn't. He stopped eating entirely. His temperature dropped. I rushed him to the vet at 6 a.m., and after a bunch of diagnostics that cost me $340 (my emergency fund wasn't amused), they diagnosed him with a combination of mild pancreatitis and what the vet delicately called 'dietary indiscretion.' It was the tuna. The sudden load of fat and potential contaminants in such a tiny, developing body was too much. Fig survived and grew up to be a magnificent orange menace who now liives with my neighbor, but those three days of 'everything is fine' nearly killed him.

I'm including this story because it demonstrates the most dangerous thing about tuna: sometimes it works perfectly for a short time, and that gives you false confidence. You think, 'Oh, my cat's different. He's fine!' And maybe he is fine the first time, the second time, the tenth time. Until he isn't. And by then, you might not connect the dots because the tuna was 'always fine before.'

What I actually tell adopters now (after yelling at them about tuna)

Look, I'm not going to stand here and say tuna is like cyanide and if your cat licks a single flake off your plate she'll keel over. That's not true. But after 14 years of this, here's the framework I give to every person who adopts a cat from me:

If you want to give tuna as an occasional treat — and I mean once every two weeks at most — use a teaspoon or less of skipjack light tuna packed in water with no added salt. Rinse it to lower sodium further. And never, ever give albacore or 'solid white' tuna, because those are the big fish with the highest mercury loads.

But honestly? I'd rather you not give tuna at all. There are so many better treat options out there. Freeze-dried chicken, tiny bits of cooked plain salmon (a different fish that has lower mercury risk), or even somtehing like bonito flakes that you can sprinkle on food to make it exciting without the mercury bomb. I've also had luck using baby food (plain chicken, no onion or garlic) for sick cats who need to eat. It works just as well as tuna water and doesn't come with a side of neurotoxin.

And if your cat is refusing to eat and you're desperate — call your vet before you reach for the can opener. I know that sounds like CYA advice, but I've been that desperate person. There are appetite stimulants, recovery foods, and feeding tubes that are actual medical solutions. Tuna isn't a medical solution; it's a gamble. I wish I'd learned that $3,000 earlier.

By the way, this obsession with giving cats random human food isn't just a tuna thing. Dogs too. I wrote about the time my build puppy ate a bottle of ibuprofen and the household safrty guide I wish I'd had before that night — that nightmare is chronicled here. The lesson's the same: what's harmless to us can wreck them.

What Miso eats now (and the $340 vet bill that explained everything)

Right now, as I type this, I've got a build cat named Miso sitting on the windowsill. She's a 2-year-old calico who came in with a host of digestive issues, and for the first few weeks I tried everything to get her to eat consistently. Did I reach for tuna? No. But I almost did. I stood in front of my pantry, can in hand, arguing with myself for a solid five minutes. I put it back. I'm proud of that.

Instead, I talked to Dr. Nguyen again (I swear, that woman should charge me a subscription fee at this point) and we worked out a food plan built on a high-quality, limited-ingredient wet food, with some warm water mixed in to make it smellier and more palatable. Miso's been stable for two moths now. No stomach issues, no weird neurological signs. Her bill for that consult and the food trial was about $340, which is exponentially less than an emergency visit for poisoning.

Sometimes I think about the fact that in a parallel universe, I'd've given Miso tuna that first week, she'd have gotten sick, and I'd be writing a very different story right now. Instead, she's here on the windwosill, staring at me like I'm the one who needs to be supervised.

She's not wrong.