Goldfish are the world's most common pet fish, but are often kept in conditions that cause significant welfare problems. Understanding fish sentience transforms our responsibility.
Goldfish welfare is compromised by two major problems: inadequate housing and the trivialisation of fish pain. Research shows goldfish experience pain and can learn from aversive experiences - they are not the simple automata popular culture suggests. A goldfish in a small, unfiltered bowl experiences chronic oxygen deficiency, ammonia poisoning, and stunted growth - all welfare harms. Providing appropriate housing with a filtered tank of at least 100 litres with adequate space and companions transforms goldfish welfare. The ban on goldfish as fairground prizes in many jurisdictions reflects growing recognition of their welfare needs.