Ranchu goldfish are beloved for their rounded bodies, lack of a dorsal fin, and distinct head growth (wen). Often referred to as the “king of goldfish” in Japan, these peaceful and graceful swimmers require a specific care approach suited to their delicate build.
In this guide, you’ll learn everything you need to care for Ranchu goldfish, from tank size and feeding to water conditions and health considerations.
Quick Species Profile
| Feature | Details |
| Scientific Name | Carassius auratus (Ranchu) |
| Common Name | Ranchu Goldfish |
| Size | 5–8 inches |
| Lifespan | 10–15 years (up to 20 with care) |
| Origin | Japan (selectively bred) |
| Temperament | Peaceful, slow swimmer |
| Tank Size | 20+ gallons per fish |
| Temperature | 65–75°F |
| pH Range | 6.5–7.5 |
Appearance
Ranchu goldfish are easily recognized by their lack of a dorsal fin, which gives them a smooth, arched back and a unique swimming style. Their prominent head growth (wen) develops as they mature, often covering the entire face. Colors range from orange, red, and white to calico and black.
Their body is compact and rounded, requiring smooth decorations and gentle filtration to avoid injury.
Lifespan
With proper care, Ranchus can live 10 to 15 years in aquariums, and up to 20 years in ideal conditions. Clean water, a stable diet, and a stress-free tank environment are essential to reach their full lifespan potential.
Ranchu Goldfish Size
Adult Ranchus typically grow between 5 and 8 inches. Their growth rate depends on tank size, diet, and water quality. Unlike slimmer goldfish types, they do not need as much swimming space but do need clean water and a low-flow tank.
Tank Size & Setup
Provide at least 20 gallons for one Ranchu, and add 10 gallons per additional fish. Ranchus are poor swimmers and do best in low-flow tanks with plenty of open swimming space.
Use sponge filters or gentle hang-on-back filters to keep the water clean without creating strong currents. Choose smooth substrate or go bare-bottom for easier maintenance.
Decorations should be soft or smooth, and hardy plants like anubias or java fern are ideal. Avoid sharp or abrasive objects that may damage their wen or body.
Water Parameters
Ranchus thrive in cool to moderate water temperatures (65–75°F) and stable water chemistry. Perform weekly water changes (25–50%) and test water frequently.
- Ammonia: 0 ppm
- Nitrite: 0 ppm
- Nitrate: <40 ppm
- pH: 6.5–7.5
Stable water conditions are more important than exact numbers.
Diet & Feeding
Ranchus require a balanced diet that supports slow, healthy growth and prevents swim bladder issues.
Feed high-quality sinking pellets or gel food formulated for fancy goldfish. Supplement with blanched veggies like peas, spinach, or zucchini. Occasionally offer treats like bloodworms or brine shrimp.
Feed once or twice daily and remove uneaten food within 2 minutes.
Behavior & Tank Mates
Ranchus are peaceful, slow swimmers that enjoy the company of similar fancy goldfish. Due to their poor swimming ability and delicate head growth, they should only be housed with other slow, gentle fish.
Compatible tank mates include:
- Oranda
- Lionhead
- Fantail
- Telescope
Avoid mixing with common or comet goldfish, or fast, competitive feeders.
Common Health Issues
The Ranchu’s wen and round body make them vulnerable to:
- Wen infections (bacterial/fungal)
- Swim bladder disorder
- Fin rot and ammonia burns
Keep the tank clean, perform regular water changes, and inspect the wen for discoloration or swelling. Quarantine new additions to prevent disease spread.
Breeding Ranchu Goldfish
Ranchus can breed in captivity. Males develop breeding tubercles during the season and chase females to trigger egg laying. Use soft spawning mops or fine-leaf plants.
Separate adults after spawning to prevent egg-eating. Feed fry with baby brine shrimp or infusoria until they are large enough for crushed pellets.
Final Thoughts
Ranchu goldfish are one of the most elegant and rewarding fancy goldfish to keep. Their gentle nature, unique look, and impressive head growth make them favorites among aquarists worldwide.
Provide clean water, soft surroundings, and a slow-flowing tank, and your Ranchu will thrive for years.
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