Fungal Outbreak in Pond Fish After Koi Relocation: Treatment Strategy

Managing Stress-Induced Fungus in a Connected Pond System

Moving 25 koi into a new pond stressed the entire system, and the shubunkins left behind developed fungal infections (cottony patches on mouth and body). The two ponds are connected by a stream, so treatment must address both.

Immediate Actions

1. Separate the ponds – shut off the stream to isolate treatment.
2. Salt bath – 0.1% pond salt (1 lb per 100 gallons) in both ponds; monitor plants (salt-tolerant species only).
3. Antifungal medication – PimaFix (herbal) or a formal malachite green/formalin blend. Remove carbon filtration during treatment.
4. Antibacterial support – MelaFix helps prevent secondary infections.

Why the Unmoved Fish Got Sick

Stress hormones (cortisol) suppress immune function. The chaos of netting koi likely stressed the shubunkins via water vibration, chase, and water-quality shifts.

Long-Term Prevention

• Quarantine all new fish 4 weeks.
• Maintain 0.05% salt continuously if plants tolerate it.
• Keep a hospital tank ready for rapid isolation.

Treat aggressively now; fungal infections spread fast in cool water.