Ranchu goldfish
Carassius auratus
intermediate careOverview
The ranchu goldfish (Carassius auratus) is the celebrated “king of goldfish” in Japan — a dorsal-less fancy with a smoothly arched back, curled tail and a wen over its head. It reaches 15–20 cm and lives 10–15 years. Having no dorsal fin makes the ranchu a slow, wobbly swimmer, so it is one of the more delicate fancies: it needs calm water, gentle companions and a carefully managed diet to stay healthy and upright.
Tank & water
Give one ranchu 75 litres (20 gallons), plus about 40 litres per extra fish. Priorities:
- No heater, stable warmth: ranchu are cold-water fish that prefer a steady 18–23 °C as a sensitive fancy.
- Gentle flow: as poor swimmers, they struggle against current — temper a good external filter outflow.
- Clean water for the wen: over-filter and keep on top of changes to protect the headgrowth.
Feeding
Ranchu are omnivores, and diet is central to their health. Use a quality sinking goldfish food so they aren’t gulping air at the surface, and include blanched peas and soft vegetables to prevent constipation and floating. Feed small amounts once or twice a day, soak pellets beforehand, and remove leftovers. Keep water pristine with regular maintenance and water testing.
Tankmates
Keep ranchu only with slow, gentle fancy goldfish — lionheads, orandas, black moors, celestials and bubble-eyes. Their weak swimming means faster fancies like ryukins, and certainly single-tails like comets, will out-compete them at feeding time. They are not tropical community fish. A group of equally slow fancies in a spacious tank is ideal — plan numbers with how many fish in an aquarium.
Serious ranchu keepers traditionally view their fish from above, since the smoothly arched back and neatly tucked tail — the traits the variety is judged on — show best looking down. That makes a broad, shallow tank or a tub an excellent home, giving the fish more floor space to potter over without deep water to fight against. Whatever the setup, a ranchu is a slow, endearing, bottom-pottering fish that rewards calm, careful keeping.
Ranchu goldfish — frequently asked questions
How big do ranchu goldfish get?
Ranchu reach around 15–20 cm as rounded, back-arched fancies with no dorsal fin. They are heavy-waste fish that still need a large, well-filtered tank — see how big do goldfish get.
Do ranchu goldfish need a heater?
No. Ranchu are cold-water fish, but as a delicate dorsal-less fancy they prefer stable, warmer water around 18–23 °C and dislike cold snaps. In most homes no heater is needed — see do goldfish need a heater.
Why is the ranchu called the king of goldfish?
It is the most prized fancy in Japanese goldfish keeping, judged on its smooth back, curled tail and headgrowth. The lack of a dorsal fin makes it a poor, wobbly swimmer, so it needs calm, gentle tankmates and sinking food.
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