Koi carp are intelligent, long-lived fish kept in garden ponds, but welfare is frequently compromised by poor water quality, predation, disease, and inadequate pond size.
Koi welfare is shaped primarily by water quality and space. Fish in chronically poor water quality experience gill damage, immune failure, and increased disease susceptibility. Wounds from heron attacks that are not immediately fatal cause prolonged distress. Koi herpesvirus kills rapidly but the prodromal period involves clear signs of distress. Because koi are long-lived and developed relationships with their keepers, welfare failures represent sustained harm to individual animals. Proper pond management is achievable and dramatically improves outcomes.