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Care guide

Ranchu care guide

A ranchu is a slow, deep-bodied fish with a compressed gut and no dorsal fin. Almost every problem keepers run into traces back to one of four things: water, food, temperature, or tankmates.

Tank or tub

Ranchu do best in wide, shallow water with a lot of surface area. Japanese breeders raise them in tubs about 30 cm (12 in) deep. In a glass tank, choose length and width over height.

  • Size: 20 gallons (75 L) for the first fish, 10 gallons (40 L) for each additional one.
  • Surface area: aim for at least 140 sq in (900 cm²) of surface per adult fish.
  • Flow: gentle. A sponge filter or a filter with a spray bar; ranchu tire in strong current.
  • Substrate: bare bottom or smooth sand. Gravel traps waste and can be swallowed.
  • Decor: nothing sharp. The head growth (wen) tears easily.

Water

Goldfish are heavy waste producers and ranchu are sensitive to ammonia. A cycled filter and a weekly routine matter more than any product.

  • Ammonia and nitrite: always 0 ppm. Nitrate under 20 ppm.
  • Water changes: 30–50% weekly, temperature-matched, dechlorinated.
  • Temperature: 65–75 °F (18–24 °C). Avoid swings of more than 2 °F a day.
  • Hardness: moderately hard (GH 8–15). Very soft water is a common cause of poor wen growth.
  • Green water: breeders use it deliberately. A light green tint is fine and helps color.

Feeding

The short, round body leaves little room for the swim bladder and gut. Floating food gulped at the surface is the number one cause of the floating and tilting keepers panic about.

  • Sinking pellets or gel food as the staple, 2–3 small feedings a day.
  • Frozen bloodworm, brine shrimp, daphnia a few times a week for growth and color.
  • Blanched peas, spinach, duckweed for fiber. Skip a day if a fish floats.
  • Amount: what they finish in about 2 minutes. Ranchu will always look hungry.

Health and tankmates

Keep ranchu only with ranchu, or with other slow round-bodied goldfish such as lionheads. Fast fish like comets and commons will outcompete them for food.

  • Swim bladder trouble: fast for 2 days, then peas; check temperature and nitrate.
  • Wen infections: white fuzzy patches in the head folds. Improve water first, then salt at 0.1–0.3%.
  • Ich and flukes: flashing and clamped fins. Treat the whole tank, not just one fish.
  • Quarantine every new arrival for 3–4 weeks. This is the single best habit you can build.
Rule of thumb: if a ranchu looks wrong, test the water before you reach for medication. Nine times out of ten the water is the medicine.

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