Why vomiting once changes the timeline
A single vomit episode after tuna suggests her stomach rejected the richness, not that she's poisoned. The vet's fluids protect against dehydration, but her electrolytes need 12–24 hours to rebalance fully. You'll see the recovery in small signs—less time spent hunched over, more interest in her surroundings—rather than sudden leaps back to normal.
Don't be alarmed if she skips a meal or two. Cats often fast briefly after stomach upset. The danger zone is 24+ hours without keeping water down—that's when to call the vet again, not for the tuna but for potential secondary issues like an inflamed pancreas.
The spoonful test for real recovery
Start with a tablespoon of water in a shallow dish after the 4-hour mark. If she laps it up without hesitation, wait 30 minutes before offering another. Success here means her nausea has passed—the tuna is out of her system, and her stomach lining is settling.
When she's kept down three rounds of water, try a teaspoon of plain boiled chicken (no salt or oil). This tests whether her gut can handle proteins again. If she walks away, don't push it—her body knows best. The return of hunger is the final green light, often around the 18-hour mark.
How canned tuna differs from raw fish reactions
Cooked tuna in cans lacks the thiaminase enzyme found in raw fish, so you don't have to watch for neurological signs like twitching or dilated pupils. The vomiting here is purely from richness or salt overload. That's why the vet likely didn't prescribe thiamine supplements—this wasn't a thiamine-depletion event.
Her litter habits post-vomit tell the real story. If she's passing normal stools (not too hard or soft) within 48 hours, the tuna caused no lasting digestive havoc. Scoop the box more frequently during recovery—you're tracking frequency and consistency, not just whether she goes.
When lethargy crosses from normal to concerning
Post-vomit sleepiness is expected, but it should gradually lessen. If she's still wholly inactive at the 24-hour mark, check her gums—they should be pink, not pale or sticky. Press a finger gently to her gums; the color should return within two seconds after you lift it (this tests capillary refill time).
Recovery isn't linear—she might nap hard after her first meal back, then perk up. What warrants another vet visit is progressive weakness, like struggling to jump onto her favorite perch or ignoring loud noises she usually reacts to. Bring the tuna can label if you go back—the vet will check for additives beyond fish that could explain prolonged symptoms.
The full verdict, portion guidance and serving notes are collected on the Tuna (canned) food facts page.