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Ranchu Goldfish
Freshwater Fish · Goldfish

Ranchu Goldfish

Carassius auratus

Dorsal-less Japanese fancy, bred to be seen from aboveIntermediate

Lifespan
10-15 years
Size
6-8 in
Social needs
Social - keep 5+ together
Time
High (careful feeding, frequent water changes)
Cost
High
Diet
Omnivore

Overview

What is this animal?

  • The ranchu is a Japanese fancy goldfish, developed from Chinese lionhead stock and called the king of goldfish in Japan.
  • It has no dorsal fin at all, a thick, broad body with a smoothly curved back, a short twin tail tucked in at a sharp angle, and a hood of raspberry-like growth, the wen, over the head, cheeks and gill covers.
  • Japanese ranchu are bred to be viewed and judged from above, so the top-view standard prizes a broad, rectangular shape seen from overhead and a wen that never covers the eyes.
  • Mature fish reach about 6-8 in, and they are gentle, slow fish that can live 10-15 years when kept well.

Temperament

  • Ranchu are peaceful, gentle and slow, and they are social fish that should be kept in a group of at least five.
  • They do best with other ranchu, or with other slow, round-bodied fancies of a similar size.
Show 2 more
  • Never keep them with comets, commons or other single-tailed goldfish, which take the food first, and watch that they are not losing out even to other fancies.
  • Tropical fish and fin-nippers do not belong with them, and a single-variety tank is the simplest way to make sure every fish eats.

A good fit for

  • Keepers who enjoy watching fish from above, in a raised pond or wide tank
  • Calm, single-variety fancy goldfish setups
  • Coldwater (unheated) setups with gentle flow
  • People committed to 10-15 years of care

Common mistakes to avoid

  • Buoyancy trouble from overfeeding or floating food
  • A wen that traps debris or grows over the eyes
  • Strong currents for a fish with no dorsal fin
  • Mixing with single-tails or faster goldfish

Enclosure

Minimum 125 gallons, for a group of 5

Cannot be kept alone. The minimum is 5, and the space above is for that group.

  • Ranchu are coldwater fish that need no heater in a normal room, and about 64-73°F suits them indoors; one UK keeper has kept ranchu in an unheated outdoor pond all year, but shop-bought fish are rarely used to a long winter and should never go straight into a pond.
  • Keep a group of at least five in a tank or raised pond at least 6.5 ft long with at least 24 in of water depth, about 127 US gallons or more, with strong filtration and a wide footprint.
  • The length is ten times, and the depth three times, the full adult length of the largest fish, so ranchu that stay at 6 in need 59 in and 18 in.
Show 2 more
  • Show breeders keep ranchu in ponds or vats with water about 10 in deep, viewed from above; that is a breeding and show tradition, and a home group needs the depth given here.
  • Ranchu are weak swimmers, so keep the flow gentle, leave plenty of open water, use only smooth stones and soft plants, and change water often, because debris and dirty water are what infect a wen.

Check your enclosure

Supplies

Setup

  • Tank and stand, at least 6.5 ft long
  • Filter
  • Thermometer
  • Substrate, plants and decor
  • Liquid test kit
  • Dechlorinator and starter supplies

Ongoing

  • Sinking goldfish pellets or gel food
  • Frozen peas (to deshell and blanch)
  • Courgette and spinach for blanching
  • Veg clip
  • Frozen bloodworm or daphnia
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  • Small cup for pre-soaking pellets
  • Fine net for removing leftovers

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

  • Check temperature and equipment
  • Feed a sinking, pre-soaked food
  • Head-count and look everyone over

Every few days

  • Top up evaporationevery 3 days

Weekly

  • Large water change
  • Test the water
  • Wipe the front glass only
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Every few weeks

  • Rinse the filter mediaevery 2 weeks
  • Trim and thin the plantsevery 2 weeks

Monthly

  • Check supplies and reagent dates
  • Replace or recharge chemical media, if you use any (skip it in a blackwater tank)

Health review: Quarterly water and buoyancy review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended sizeWhat will it cost?Setup, monthly and over its whole life, itemisedIs this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore
  • Ranchu are omnivores with deep bodies that are prone to buoyancy trouble, so feed a quality sinking goldfish pellet or gel food as the staple, with blanched vegetables and other plant matter, plus occasional frozen bloodworm or daphnia.
  • Pre-soak dry food, which reduces gulped air and bloating.
  • Feed small meals once or twice a day, only what is eaten in a couple of minutes; breeders feed youngsters up to six times a day to grow them on, but a pet adult does not need it.
  • Avoid floating flake and overfeeding, both of which lead to the floating and tilting these fish are prone to.

Health

Signs of good health, and the common problems
  • Without a dorsal fin a ranchu rolls and yaws as it swims and tires sooner than a single-tailed goldfish, and its deep body makes swim-bladder and buoyancy problems common.
  • Watch for floating, sinking or tilting after meals, resting on the bottom, clamped fins and flicking, and treat each first as a question of diet and water quality.
  • The wen needs watching too.
  • Its folds can trap debris and become infected, and in some fish, and some strains, it grows over the eyes; a wen spreading over the eyes needs a vet who treats fish.
  • Ranchu are very sensitive to ammonia and nitrite, so keep the system fully cycled and change water often.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.
Now
Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.
Now
Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.
Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.
Today
White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.
Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.
A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.
safe
Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.
safe
Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.
safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.
with a caveat
Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.
with a caveat
Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.
with a caveat
Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.
with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.
never
Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.
never

This is our general list for freshwater fish. We have not built one specific to Goldfish yet.

Top resources for more info

Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-10-22.

YouTubers

Luke's GoldiesGoldfish keeping indoors and in ponds, from a breederGirl Talks FishCare how-tos by fish type, tank setup and beginner mistakes (the host works for Aquarium Co-Op, a retailer)Aquarium Co-OpSpecies care guides, filtration and fish health (run by a retailer)

Sites

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Is your enclosure big enough?

These are the smallest sizes that give good conditions, not legal minimums. More room is always better.

Minimum 125 gallons, for a group of 5

Every figure, and where it comes from

125 gallons is for a group of five ranchu, in a tank or raised pond at least 6.5 ft long with at least 24 in of water depth. Austrian law requires a goldfish tank at least ten times as long, and three times as deep, as the full adult length of its largest fish (here 8 in), and at least five goldfish kept together. Show breeders keep ranchu in ponds or vats with water about 10 in deep, to be viewed from above, and the welfare-led sources ask for less length; Austrian law allows smaller tanks only for breeding, for showing single fish or pairs, and at competitions, so this site sets its figure at the legal minimum because good conditions are never less than a law requires. Ranchu that stay at 6 in need 59 in and 18 in.

Minimum volume125 gallons
Swimming length6.5 ft minimum. A tall tank of the right volume is still the wrong shape.
CompanyCannot be kept alone. The minimum is 5, and the space above is for that group.
The recognised standards do not agree on this one
Austria, 2. Tierhaltungsverordnung, Anlage 5: A tank at least 10 times as long and 3 times as deep as the full adult total length of the largest fish, at least 39 x 16 x 20 in (53 gallons), and at least five goldfish kept together; smaller tanks are allowed only for breeding, for showing single fish or pairs, and at competitions. A legal minimum. The welfare-led sources ask for less, so this is the length, depth and group this site uses: good conditions are never less than a law requires. Checked 2026-10-23.
Practical Fishkeeping (UK), on the breeders of the Ranchu Brotherhood: Ranchu are kept in ponds or vats for the most growing and swimming room, with water about 10 in deep in most cases, and are bred to be viewed from above. A breeding and show tradition, shallower than the figure used here. Checked 2026-10-23.
Practical Fishkeeping (UK), fancy goldfish guide: A tank at least six times as long and twice as wide as a typical adult; mature ranchu reach 6-8 in. Less length than the figure used here: 47 in for an 8-inch fish. Checked 2026-10-23.
Maidenhead Aquatics (UK retailer), fishkeeper.co.uk: Ranchu grow to 8 in and should be kept in groups, in an aquarium ideally about 47 in long. Less length than the figure used here. Checked 2026-10-23.
Swiss Animal Protection STS: A goldfish aquarium at least 47 in long and 20 in wide; goldfish are shoaling fish and must not be kept alone. Less length than the figure used here. Checked 2026-10-23.
RSPCA Australia: Length at least 4 times, width 2 times and height 3 times the adult body length, and never under 13 gallons. Its width, 16 in for an 8-inch fish, is the width behind the volume used here, and its height, 24 in, matches the depth; its length is less. Checked 2026-10-23.

What it really costs

Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.

My kit says 0.25 ppm. Is that dangerous?

A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature. Each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.