Why butter hits cats harder than fish
That single spoonful's real issue isn't the halibut—it's the butter coating it. Cats lack efficient enzymes to process high-fat dairy, causing almost immediate stomach rebellion. The vomiting you saw is her body's emergency eject button for the offending lipids.
For a 6 kg cat, even a teaspoon of butter can overwhelm her digestive capacity. Unlike dogs, cats can't adjust bile production quickly enough to handle sudden fat intake, hence the rapid reaction within hours of eating.
The first 12 hours after vomiting
Remove all food for 4-6 hours to let her stomach settle, but keep water available in small, frequent portions. Dehydration from vomiting poses more risk than temporary fasting for an adult cat her size.
When reintroducing food, start with a tablespoon of her regular diet rather than offering alternatives. Watch for productive chewing and swallowing—painful gulping or neck stretching suggests residual nausea needing vet assessment.
Hidden dangers in pan residues
Buttery halibut often means garlic or onion powder in the cooking pan, even if you didn't see seasonings. These allium family additives are far more toxic to cats than the butter itself but may not cause immediate signs.
Check her gums for unusual paleness over the next 48 hours, and note any changes in urination habits. These delayed signs would indicate something beyond simple fat intolerance and warrant urgent blood tests.
When the next vomit means go
One isolated vomit episode may resolve on its own, but consecutive vomiting within eight hours or lethargy developing after the first purge means stop waiting. Her 6 kg body can't afford prolonged fluid and electrolyte loss.
Save a sample of any further vomit in a ziplock bag for the vet. Food-borne illness from spoiled fish would look different than butter reaction—chunky undigested pieces versus slick yellow foam helps determine the true culprit.
The full verdict, portion guidance and serving notes are collected on the Halibut food facts page.