Koi and pond fish are often kept in conditions that cause chronic stress despite being perceived as low-maintenance pets.
Koi welfare is frequently compromised by underdeveloped ponds, inadequate filtration, and overstocking. Like aquarium fish, koi demonstrate preferences, show stress responses, and form social relationships. Chronic poor water quality causes slow, uncomfortable deterioration rather than acute distress — making it easy for owners to overlook. Koi represent a long-term, significant welfare commitment.