Aquatic Animals

The Welfare of Koi and Ornamental Fish

Koi and ornamental fish are highly valued animals that nonetheless frequently suffer from inadequate pond or tank conditions, poor water quality, and disease.

Key Facts

High-quality koi can be worth tens of thousands of dollars but receive inadequate care
Koi require large volumes of water — a minimum of 1,000 liters per fish is recommended
Most ornamental fish disease is caused by preventable water quality problems
Koi herpesvirus causes mass mortality and significant suffering in affected ponds
Import trade brings disease-carrying fish into established populations

Welfare Considerations

The paradox of ornamental fish welfare is that animals with high monetary value often receive poor welfare due to gaps in keeper knowledge rather than financial neglect. Water chemistry, volume, temperature, and filtration are the determinants of fish health and welfare, and most failures are caused by inadequate system design or lack of monitoring. Disease in koi causes ulceration, respiratory distress, and buoyancy problems that represent significant suffering.

What You Can Do

Research water volume, filtration, and chemistry requirements before acquiring koi
Test pond water chemistry weekly for pH, ammonia, nitrite, and nitrate
Quarantine all new fish before adding them to an established population
Find a veterinarian experienced with ornamental fish health before problems occur