Tropical Fish, any small fish that can be kept successfully in a warm-water aquarium. Most such fish are native to tropical regions. However, some fish that can be found in cooler water in the wild state have been developed by selective breeding into domestic varieties that thrive best in warm-water aquariums. In aquariums, tropical fish live an average of two to three years. A few survive for 10 years or more.

Tropical fish are valued for their delicate or brilliant colors, attractive or unusual shapes, lively and graceful movement, and interesting habits. Most tropical fish range in length from one to five inches (2.5 to 12.5 cm). In the United States, keeping and breeding tropical fish in home aquariums began in the late 1920's and became a popular hobby after World War II. In many countries, including the United States, there are organizations and publications devoted exclusively to the hobby.

Most aquarists (keepers of aquariums) prefer freshwater fish, because it is more difficult to provide saltwater varieties with a suitable environment. Also, saltwater fish are more expensive, because it is harder to collect and ship them. More than 1,500 varieties of freshwater tropical fish have been successfully kept in home aquariums; of these, about 500 varieties are usually available commercially. Goldfish are the most popular aquarium fish, but some experts do not consider them to be tropical because they do not need particularly warm water.