Yes, cats can eat tuna — but it should be an occasional treat, not a diet staple. Tuna is high in protein and most cats go absolutely wild for it, but regular feeding carries real risks including mercury exposure and a condition called thiamine deficiency. Small amounts, offered rarely, are generally fine for healthy adult cats.
Why Cats Love Tuna (And Why That's a Problem)
Cats are obligate carnivores with a strong drive toward high-protein, high-fat foods. Tuna hits all those instinctual buttons — it's pungent, rich, and intensely flavored. The problem is that this attraction can work against you. Some cats become so fixated on tuna that they'll refuse other foods entirely, a pattern sometimes called "tuna addiction."
A cat that only eats tuna is a cat with serious nutritional gaps. Plain tuna — whether canned or fresh — doesn't contain the full range of nutrients cats need, including adequate taurine, vitamin E, and the right calcium-to-phosphorus balance. Over time, an all-tuna diet can lead to genuine health problems.
The Mercury Problem
Tuna is a large, long-lived predatory fish. That means it accumulates mercury from the smaller fish it eats throughout its life — a process called bioaccumulation. For humans eating a varied diet, occasional tuna is considered low-risk. For a small cat eating tuna regularly, the math looks different.
There's no established "safe" mercury threshold published specifically for cats, but the concern from veterinary nutritionists is consistent: frequent tuna feeding increases mercury exposure in a way that wouldn't happen with a balanced commercial diet. Albacore (white) tuna generally contains more mercury than light tuna, so if you're going to offer tuna occasionally, light tuna in water is the lower-risk choice.
Thiamine Deficiency: The Less-Known Risk
Raw tuna contains an enzyme called thiaminase, which breaks down thiamine (vitamin B1) in the body. Thiamine is essential for cats' neurological function, and deficiency can cause serious symptoms. Cooking deactivates thiaminase, so canned tuna doesn't carry this particular risk — but it's a strong reason never to make raw tuna a regular part of your cat's diet.
Commercial cat foods are formulated to meet thiamine requirements. If tuna is replacing a meaningful portion of a balanced diet, that safety net disappears.
What About Steatitis?
Steatitis — sometimes called yellow fat disease — is a painful inflammatory condition historically linked to cats fed large amounts of unsaturated fatty fish, including tuna. It's associated with vitamin E deficiency. While steatitis is less common now than it was when raw or home-fed tuna diets were more widespread, it's still a documented risk of heavy tuna feeding. Your vet can tell you more if you're concerned.
How Much Tuna Is Too Much?
There's no single number that every veterinarian agrees on, but a common working guideline is that fish-based treats — including tuna — should make up no more than 10% of a cat's total calorie intake. For most average-sized adult cats, that translates to a small amount a few times per week at most, not daily.
Practically speaking, a teaspoon or so of plain canned tuna a couple of times a week is unlikely to cause problems in a healthy adult cat eating a complete and balanced main diet. Daily feeding, or using tuna as a meal replacement, crosses into territory where risks start to compound.
Kittens, senior cats, and cats with kidney disease, thyroid conditions, or other health issues need individual guidance from a vet — the general guidelines don't necessarily apply.
Canned Tuna vs. Fresh Tuna vs. Cat Food with Tuna
These aren't all the same thing, and it's worth understanding the differences.
Canned tuna for humans: This is where most cat owners reach first. If you're going to offer it, choose tuna packed in water, not oil, and with no added salt. Oil-packed tuna is higher in fat than cats need as a snack, and sodium can add up quickly. Even "low sodium" human canned tuna can be saltier than ideal.
Fresh tuna: Same mercury concerns apply, plus the thiaminase issue if served raw. If you're cooking fresh tuna for yourself and want to share a small plain piece with your cat, that's reasonable — just keep portions small and skip any seasonings, oils, or marinades entirely. Onion and garlic in particular are toxic to cats.
Commercial cat food with tuna: Tuna-flavored or tuna-based cat foods formulated to AAFCO standards are a different story. These are balanced to meet cats' nutritional needs, they typically use smaller amounts of fish alongside other ingredients, and they've been tested to appropriate safety standards. Using a tuna-flavored complete food as a main diet is not the same as feeding plain canned tuna.
Tuna cat treats: Tuna-based cat treats in small amounts are fine for most healthy cats. Just follow the serving size on the packaging and factor them into your overall treat budget.
Signs You May Be Feeding Too Much Tuna
Watch for these if tuna has become a regular part of your cat's diet:
- Refusing their regular food unless tuna is offered alongside it
- Weight changes — tuna can be calorie-dense, or if it's replacing meals, your cat may not be eating enough overall
- Coat changes or skin issues, which can sometimes reflect nutritional imbalances
- Digestive upset — some cats have sensitive stomachs and tuna triggers loose stools
None of these symptoms are specific to tuna, so a vet visit is the right call if you notice changes.
Tracking What Your Cat Actually Eats
One place where pet owners often lose track is in the cumulative effect of treats, toppers, and snacks. A little tuna here, some chicken broth there — it adds up, and it can quietly push your cat's diet out of balance without you realizing it. The Pet AI Nutrition Tracker app can help you log those extras alongside your cat's main meals so you have a clearer picture of what they're actually consuming day to day.
The Bottom Line
Tuna is not toxic to cats in the way that onions or chocolate are. But "not toxic" isn't the same as "safe to feed freely." The real risks — mercury accumulation, nutritional imbalance, and the risk of a cat who refuses anything else — come from frequency and quantity, not from the occasional bite.
Keep tuna as a sometimes treat, stick to plain canned tuna in water with no added salt, and make sure it's adding to a balanced diet rather than replacing one. That's a reasonable, realistic approach for most healthy adult cats.