| Verdict for dogs | 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 |
A little plain tuna canned in water is not toxic, but tuna carries more mercury than most fish and tuna in oil or brine adds fat and salt. Fine as an occasional taste, not as a regular food.
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 dog seems unwell.
Never induce vomiting and never give any medicine unless a vet tells you to — it can do more damage than the poison. What we will and won't tell you.
If you're sharing food because you want to treat them, a treat formulated for dogs does the job without the guesswork.
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Can cats eat tuna? — Feed with caution to cats.
Not toxic, but be careful — tuna isn't poisonous to dogs, and it comes with caveats that matter. A little plain tuna canned in water is not toxic, but tuna carries more mercury than most fish and tuna in oil or brine adds fat and salt. Fine as an occasional taste, not as a regular food.
Watch for: Vomiting; Diarrhea or loose stools; Loss of appetite; Belly discomfort or unusual tiredness. Some signs lag by a day — call, don't wait.
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.