Butterfly Koi Bullied and Injured: Parasites or Bacteria Likely

9x16 ft pond, 25 fish, one butterfly koi lies on bottom, jammed in rocks, then floats to skimmer. Other fish attack it; fins red/torn. Owner moved it to hospital tank.

Primary Suspect: Disease Making It a Target

Healthy fish don’t get bullied. The koi likely has parasites (flukes, trichodina) or bacterial infection causing lethargy. Flashing (rubbing) would confirm parasites.

Immediate Steps

1. Water test: Ammonia, nitrite, pH, KH.
2. Microscope scrape: Only way to ID parasites.
3. Broad-spectrum antiparasitic in quarantine if no scope access.
4. Wound care: Topical antiseptic (propolis, iodine) on torn fins.
5. Isolate until healed: Reintroduce only when behavior normal.

References for parasite ID: wittestip3, Lernaea, koiziekten.