Goldfish with White Mouth Lesions: Columnaris Risk & Quarantine Failure

New goldfish shows swollen white mouth, "hair-like" filaments, white on lower fin — classic Columnaris (Flavobacterium columnare) or fungal superinfection. The dealer treated for same disease — do not add to your pond.

Red Flags

• Dealer had outbreak — bought from infected system.
• Lesions progressing (whiteness larger in 24 hrs).
• Mouth texture abnormal — "bitty," rotting appearance.
• Acting normal — Columnaris often shows no behavioral change until late stage.

Immediate Actions

1. Do not net into main pond. Even 1 fish can introduce pathogen.
2. Set up quarantine tank: 20+ gal, cycled filter, heater (75°F), aeration.
3. Treat with: Kanaplex (kanamycin) + Furan-2 (nitrofurazone) — broad-spectrum for Columnaris.
4. Salt bath: 0.3% (3 tsp/gal) for 10 min daily — adjunct only.
5. Observe 4 weeks — no symptoms, no shedding = safe.

Systemic Fix

• Change source: Buy from breeder/importer with health history — not pet store tanks.
• Quarantine EVERY fish: 4 weeks minimum. No exceptions.
• UV sterilizer on main pond — reduces free-swimming pathogens.

Gender Note

White mouth ≠ male breeding stars (those are on gill covers/pectoral fins, not lips). This is pathology.

You dodged a bullet catching it early. Quarantine isn't optional — it's the only firewall between your pond and the pet trade's diseases.