Ranchu

Carassius auratus

Also known as: Ranchu goldfish, Buffalo-head goldfish

Water Parameters

• Temperature: 18–24°C
• pH: 7–8.4
• Hardness (GH): 89–357 ppm (5–20 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

Revered in Japan as the 'king of goldfish', the ranchu is a dorsal-less fancy with a smoothly arched back, a stubby downturned tail, and a developed wen over the head, bred for generations to be viewed from above. The absence of a dorsal fin makes it a slow, rolling swimmer with limited manoeuvrability, which shapes everything about its care: gentle water flow, no sharp decor, a sinking and easily-digested diet, and tankmates restricted to other slow, dorsal-less or delicate fancies. It is one of the more demanding goldfish, prone to buoyancy problems and best kept in pristine, stable, cool water by a keeper willing to attend to it. Reaching 12 to 18cm, and prized and sometimes costly in quality specimens, the ranchu rewards experienced fancy-goldfish keepers, but it is not a first goldfish.

Tankmates

The ranchu has no dorsal fin and a heavy, arched body, which makes it a slow, ponderous swimmer that must only be kept with other equally slow fancies: bubble eyes, pearlscales, black moors, and other dorsal-less types. It cannot compete with single-tailed goldfish or even the faster fancies (fantails, ryukins), which beat it to every meal, and it should never be housed with them. Its lack of a dorsal fin also makes it less manoeuvrable, so it needs gentle filter flow and no strong currents. Small fish and shrimp are unsuitable. It needs pristine, cool but not cold, very stable water.

Compatible with

• Black Moor
• Pearlscale
• Bubble Eye

Avoid keeping with

• Common Goldfish
• Comet Goldfish
• Shubunkin
• Fantail Goldfish
• Ryukin
• Cherry Shrimp
• Tropical Warm Water Species

Common Problems

• swim bladder and buoyancy problems from its round, finless body
• poor swimming ability in strong filter flow
• being outcompeted by any faster goldfish
• wen infection or overgrowth in poor water

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20