Koi are ornamental carp kept in garden ponds and valued for their striking colours. Their welfare requires large, well-filtered ponds and specialist veterinary care that many keepers do not provide.
Koi welfare involves chronic welfare risks from inadequate pond size, insufficient filtration, and disease pressure. Many garden ponds are too small and too shallow for koi, particularly in winter when ponds freeze. Koi shows and transport for competition cause acute stress and are a primary vector for Koi Herpesvirus spread. Veterinary care for koi is expensive and specialist — health problems frequently go untreated. The premium price of show koi has not translated into commensurately high welfare standards across the hobby.