The Ryūkin (琉金) is a short deep-bodied fancy goldfish with a characteristic hump in the shoulder region.

[2][3] Ryūkin come in deep-red, red-and-white, white, silver, blue, black, orange, lavender grey, iron and calico coloration.

[2][3] The ryūkin is a fine aquarium fish that can reach up to 8 inches (21 centimeters) in length.

Some ryukins are reported to grow up to 10 inches in large aquariums and commercial ponds.

Early Japanese literature refers to the ryukin as the onaga (longtail) or the nagasaki goldfish.