Tropical fish are among the most commonly kept pets globally, but poor understanding of their needs leads to widespread welfare suffering from inappropriate tank size, water quality, and species incompatibility.
Tropical fish welfare suffers profoundly from the widespread belief that fish do not feel pain or stress. Fish kept in undersized tanks experience chronic overcrowding stress, oxygen depletion, and ammonia toxicity from inadequate filtration. Species incompatibility - combining aggressive and passive species - causes injury and chronic fear stress. Wild-caught fish experience trauma during capture, transport, and adaptation to captive conditions. Betta fish kept in cups or small vases cannot thermoregulate properly and suffer from inadequate oxygen. The welfare baseline for fish keeping should include appropriately sized, cycled tanks with species-appropriate conditions and companionship.