Pet fish are the most commonly kept companion animal globally but receive the least welfare attention, with their housing and care standards vastly inferior to mammals and birds.
Fish welfare in the aquarium hobby is the lowest-attended welfare problem relative to the number of animals affected. Common practices including goldfish bowls, undersized tanks, and failure to cycle aquariums cause unnecessary suffering and premature death to hundreds of millions of individual animals. Basic education about nitrogen cycling, appropriate tank size, and compatible species would dramatically reduce this suffering.