The Sumo-Inspired Japanese Ranchu Goldfish

The Sumo Fish

In the 1800s, Japanese aquarists bred different types of the Chinese lionhead goldfish, which is known for its hooded, raspberry-like head. Inspired by Japanese sumo wrestlers, these aquarists crossbed different lionhead goldfish specifically for their short, round bodies and large heads. Thus, the Japanese ranchu goldfish, or Carassius auratus auratus, was born. 

In the Wild

Like other aquarium goldfish, the ranchu goldfish is likely descended from the Prussian carp, which originated in Asian freshwaters. Much like their aquarium and koi pond descendents, the Prussian carps inhabited shallow and slow-moving streams and ponds in the wild. Now, the ranchu goldfish is only found in captivity, where it is bred for its unique features and is prized in shows.

In the Tank

As aquarium fish, the ranchu goldfish’s short body and round head make them much like the sumo wrestlers in which their creation was inspired, but their lack of dorsal fin makes them incredibly slow swimmers. Their fantail provides some movement, but typically these fish should be kept with other goldfish species that lack a dorsal fin, so there is no competition for food from faster fish. Ranchu goldfish can typically survive on flake fish food, but some owners choose to feed them brine shrimp and bloodworms.

These fish are reasonably easy to care for, but they will need very clean tanks with filtration in order to ensure full hood development. They should be kept in tanks no less than 10 gallons, and in addition to being paired with similar goldfish, bottom-feeders like snails are a good choice in order to help keep the tank clean.

Being one of the smaller species of goldfish, the ranchu can become rather large at about 5” in bigger aquariums. Though ranchus are usually blue, black, or orange, this species can also be tri-colored, white, red, gold, or calico depending on the breeding. Male and female ranchu goldfish are similar in size, shape, and color, but typically male ranchus will develop a much more defined hood.


In shows and competitions, aquarists judge the Japanese ranchu goldfish on the definition of its hood. Usually viewing the fish from above in a shallow bowl tank, the judges also look for no dorsal fin, a short egg-shaped body, and quality of color.

Regardless if you’re showing your Japanese ranchu goldfish or not, this fish can be an interesting addition to your tank.

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