| Verdict for cats | Caution |
| Severity | 2 / 5 — Mild — usually stomach upset; watch them. |
| Safe amount | A taste at most |
| Category | Protein |
| Source | VCA Animal Hospitals — pet health library · reviewed 2026-08-07 · confidence: high |
Cats love it, which is the problem. Tuna is not nutritionally complete, some cats become fussy and refuse balanced food, and a diet of it risks mercury exposure and, with raw or excessive fish, thiamine deficiency. Occasional plain tuna in water only.
Don't make it a habit. Watch for vomiting, diarrhea or a lost appetite over the next day and call your vet if it doesn't settle or your cat seems unwell.
Never induce vomiting and never give any medicine unless a vet tells you to. With some substances it causes more damage than the poison. This page tells you when to get help — it never tells you how to treat at home.
If you're sharing food because you want to treat them, a treat formulated for cats does the job without the guesswork.
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Can dogs eat tuna? — Feed with caution to dogs.
Not toxic, but be careful — tuna isn't poisonous to cats, and it comes with caveats that matter. Cats love it, which is the problem. Tuna is not nutritionally complete, some cats become fussy and refuse balanced food, and a diet of it risks mercury exposure and, with raw or excessive fish, thiamine deficiency. Occasional plain tuna in water only.
Watch for: Vomiting; Diarrhea or loose stools; Loss of appetite; Belly discomfort or unusual tiredness. Signs can take hours or, for some poisons, a day or more to appear, so call your vet rather than waiting to see.
The safe amount is a taste at most, as an occasional treat rather than a daily habit. Large amounts mainly cause stomach upset; if that doesn't settle within a day, call your vet.