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My 4-kg indoor cat ate some expired canned tuna in water that was left open in the fridge for 5 days. She vomited once. What now?

Cats · Food safety

Last reviewed: 2026-09-05 · Reference ranges: ASPCA, Pet Poison Helpline & Merck Veterinary Manual

Short answer

The main concern here is spoilage, not the tuna itself. Expired, opened tuna can grow bacteria that cause vomiting, diarrhea, and lethargy. A single vomit may be her stomach's reaction, but you need to watch her closely. Remove all food for a few hours, then offer a small amount of her regular diet and fresh water. If she vomits again, seems lethargic, or has diarrhea, call your vet. For future safety, stick to fresh, plain tuna in water as a very occasional treat and never leave it out.

Tuna (canned) — Food safety facts

Feed with care · Cats · full breakdown on the linked food page

Occasional small amounts in water (not oil, not seasoned) are okay. Mercury builds up — do not feed regularly, especially to cats.

Dogs and cats carry the same rating (Feed with care), so the notes below hold for either pet.

Tuna (canned) is not poisonous to cats, but it is easy to over-feed. Rich fat, salt or seasoning can bring on vomiting or diarrhoea within a day, and repeated large portions are a recognised trigger for pancreatitis.

If it ate some before you noticed, watch for vomiting, diarrhoea, loss of appetite, unusual tiredness or a painful, swollen abdomen over the next 24 hours. A one-off small amount in a healthy adult usually passes with water and rest; repeated exposure, a puppy or kitten, a senior, or a pet with an ongoing illness is a reason to call your vet the same day.

Tuna (canned) can turn up now and then, but not as a daily habit: keep the rest of the day's food unchanged and watch the litter box and how quickly they finish the next meal.

The full verdict, portion guidance and serving notes are collected on the Tuna (canned) food facts page.

Open the full food page: Tuna (canned) food facts →

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