Freezer storage doesn't kill all parasites
Home freezers rarely reach the consistent sub-zero temperatures needed to neutralize fish parasites like anisakis. Your 5 kg cat ingested larvae that survive freezing, which can embed in their stomach lining. While some cats show no symptoms, others develop sudden vomiting with thread-like worms visible in the vomit within 48 hours.
The raw fish also carries bacteria like listeria that thrive in cold temperatures. These cause different symptoms — fever, neck stiffness, or circling behavior. Unlike dogs, cats often hide illness until it's advanced. Check their litter box for mucus-covered stools, which indicate gut irritation from either parasites or bacteria. Fresh raw fish is risky enough without the added variables of freezing and thawing.
Why cooking changes everything
Proper cooking does three things: kills parasites, destroys harmful bacteria, and breaks down thiaminase enzymes that interfere with vitamin B absorption. The quick sear you'd give a fillet for yourself isn't enough — cat-safe fish must be cooked through to 63°C internally, with no translucent pink areas remaining.
If you choose to offer haddock again, poach it in plain water until it flakes easily. Remove all bones — even small ones can lodge in a cat's throat or intestines. Let it cool completely, then chop into pea-sized pieces. Start with just one or two pieces to test tolerance before making it a regular treat. Never mix raw and cooked fish in the same meal period.
Comparing wild-caught and farmed haddock risks
Wild haddock carries higher parasite loads but fewer antibiotic residues, while farmed versions may contain aquaculture chemicals but fewer worms. Neither is 'safer' raw — both require cooking. The fillet your cat ate likely came from a commercial fishery where fish are flash-frozen aboard ships, but that process aims to preserve quality rather than ensure pet safety.
Check your freezer's temperature setting; home units typically run at -18°C, whereas commercial parasite-killing freezers maintain -35°C for 15+ hours. Even properly frozen fish loses texture and nutrients over time — that forgotten fillet from months ago poses more dehydration and oxidation risks than a fresh catch. When in doubt, cook it thoroughly or discard it.
When raw fish ingestion warrants a vet visit
Watch for specific red flags: vomiting that continues past 12 hours, blood in stool, or sudden disorientation. These suggest either parasite migration or bacterial infection setting in. Less obvious signs include increased thirst or urination, which could indicate kidney strain from fighting off pathogens.
Going forward, store fish in sealed containers on the freezer's coldest shelf — not the door where temperatures fluctuate. Consider keeping a small bag of cooked, portioned haddock cubes specifically for cat treats. If your cat seems obsessed with raw fish, have their vitamin levels checked — some deficiencies drive unusual cravings. For now, let their system process this incident before introducing any new proteins.
The full verdict, portion guidance and serving notes are collected on the Haddock food facts page.