Danio is a genus of small freshwater fish commonly found in rivers and streams across South and Southeast Asia. They are popular in the aquarium trade due to their vibrant colors and active behavior. The most well-known species is the zebrafish, which is often used in scientific research because of its transparent embryos and rapid development. These fish typically grow to about 2 to 3 inches in length and thrive in schools, making them social creatures. Danios are hardy and adaptable, able to live in a range of water conditions, which makes them suitable for both beginner and experienced aquarists.