Ryukin fancy goldfish fact file

Big, bold, and with a booty that Kim Kardashian would be jealous of, the Ryukin goldfish has many fans. 

All fancy goldfish started off in China, although the Ryukin is so-called because the variety was traded with the Japanese and entered via the Ryukyus – a chain of islands south of the main island of Japan. Reference is made to the Ryukin in Japanese publications dating back to 1825, and by 1908 Shinnosuke Matsubara, Director of the Imperial Fisheries Institute, Tokyo, referenced it as one of the four most popular Japanese goldfish varieties, along with the Wakin, Ranchu, and Oranda.

These days few if any Japanese Ryukin come to the UK, and most would be of Chinese origin, with Thailand being a very up and coming supply source too. Google Ryukin, and it will be Chinese fish you will see. The same in the UK fish shops.  


Ryukin can attain a body length of 20cm and a body height of that too. Combine that huge belly of perhaps 7-10cm girth on an adult fish, and an adult Ryukin could weigh a kg or more. Exceptional fish could grow larger, and that’s without fins, so life in small aquariums will stunt them.

I now believe, although this is anecdotal, that to obtain maximum body depth, Ryukin should be kept in deep water. Last year I saw some single tail Ryukin (called Tamasaba,) of 5cm body size placed into a heated koi pond containing large koi. They were added in March, fed six times per day on koi pellets, and by September they were netted out of the pond with a body size of 20cm. That’s in just six months. Notable also however was how the body depth of the fish had altered dramatically.

Going in, the fish had what I considered poor body shape for Ryukin – little to no hump backs between the head and dorsal fin, and quite slender bodies. By September the fish had steeply arched backs with prominent humps, and this I put down to the depth of the pond, of some four feet or more. 

Aquarium or pond?

So based on that account are Ryukin pond fish? If I were to attempt to house adult fish indoors I would use an aquarium of at least 120x60x60cm, preferably taller. Smaller fish can, of course, be kept in smaller tanks as they grow, but ultimately you would need a large tank. A pond suits Ryukin in so many ways – purpose-built, solids handling filtration, as much room as they would ever require and ease of large scale water changes by simply flushing filters to waste.

A heated koi pond would be a paradise for a Ryukin, although I would have them in there on their own, without the koi. I myself have kept Ryukin outside in a pond for some seven years now, but I can’t afford to heat mine and over those seven years I’ve lost probably half my fish, and always in the long, cold seasons. Being able to bring them inside and not let them get too cold would definitely aid them.


Baby Ryukin should be fed on newly hatched, live Artemia, moving on to powdered dry food, and either frozen or live Daphnia and Bloodworm. Once at a few cm body size, combine frozen and live foods with a staple of small, sinking pellets, aimed specifically at goldfish varieties. These will encourage growth and colour, and being sinking, will help to minimise the likelihood of them turning upside down with the dreaded swim bladder problems that plague them and other fancy goldfish varieties.

Ryukin should be fed several times per day, with breeders feeding perhaps six times per day to encourage maximum growth potential in these greedy fish. If you can’t be around to feed two or three times per day invest in an automatic feeder, which sinking pellets will suit well. Masses of food will mean masses of fish poo, so you’ll need effective mechanical and biological filtration, aeration from an airstone for both fish and filter bacteria, and lots of regular water changes with dechlorinated water. 

If keeping large fancy goldfish indoors in an aquarium, owners will come to recognise the pong that water will sometimes have. This is part and parcel of keeping large “carp,” so remove as much solid waste as possible during maintenance, run carbon in the filter, which can help to remove odour, and use the smell as an indicator to you that water needs changing, or of overfeeding. Froth on the surface will indicate the water needs changing too. Bubbles should pop on the surface of the water. If they hang around in a slime, change the water.


The Ryukin is a line bred form of the original goldfish, Carassius auratus. Key characteristics are that humped back, tall body profile and large belly. The tail should be twin lobed, and paired with twin anal fins, although single anal finned fish are common. Ryukin body shape is pretty much standard. A good pedigree has the steep back from head to dorsal fin, although tail length and shape can vary enormously. 

Japanese fish are known for their long, flowing tails. Chinese Ryukin, increasingly, have short tails. Long tails increase surface area, and liability to infection. Short tails cause head standing, poor swimming, and I think the most susceptibility to the fish floating upside-down. So I prefer a fish with a medium-length tail, which also aids balance. Look at Ryukin from above and tails can vary even more, from butterfly shaped tails, to wrap around fins almost like that of a Tosakin, to fantails, broad tails, ribbon tails, and veiltails.

For colour, the original fish were metallic orange, although favoured by the Japanese were red and white fish. Calico or nacreous, fish came much later by crossing with other nacreous varieties and calico Ryukin are popular the world over. Find a decent fancy goldfish supplier and you’ll get to choose from red, white, red and white, Sakura, which is a matt red and white, tricolour, calico, bronze, blue, red and black and everything in between. Tri-colours command some of the highest prices and just like with any pedigree breed, unusual or particularly striking fish are the most sought after. 

The most expensive fish I have ever seen were huge, and on sale in the UK for £3500. Yes £3500. A really nice, freshly imported fish may be upwards of £500, although thankfully the vast majority of small, common or garden Ryukin are on sale for upwards of just £5.

All fish are shipped around the world in polystyrene boxes, so the bigger the fish, the fewer you can fit in that box, and the more the fraction of the total airfreight bill for that fish becomes. That’s why Ryukin pricing rises exponentially. The smart money is to buy small fish and grow them, or pay for two good fish, and breed them as soon as you can.


Breeding Ryukin is relatively straight forward. All goldfish are non-pair-forming egg scatterers, so you just need a mature female fish, who become rounder in the belly and even lopsided as the eggs inside them develop, and a sexually mature male.

Males will typically be more slender than females, often smaller, yet they will develop visible white spots on their gill covers, which can be seen with the naked eye, and ridges on the leading edge of their pectoral fins, which can be seen, and even felt for by running a wet finger and thumb along them. 

Being seasonal spawners, Ryukin spawning is triggered by an increase in daylight, and increase in temperature (with 20C being ideal,) and an increase in food. Leave them to their own devices as fish will often spawn early in the morning, on a sunny day. In an aquarium this can mean placing the tank to actually catch sunlight, and leaving curtains open.

The male fish chases the female and nudges her belly, which becomes very soft to the touch. In nature a female Carassius auratus is driven into plants where the eggs are released, and stick to them. The male releases milt at the same time. In captivity, and with Ryukin, you will also need either live plants, woollen spawning mops, or spawning mats or brushes, also available for Koi carp. 

Outnumbering the female by two to one can aid spawning, as then a male each side of the female will help to force her into the plants, trap her, and squeeze her. Ryukin can also be hand stripped by experienced breeders. For best results the water should be warm, shallow, clean, and still, apart from some gentle aeration from an airstone. Remove the parent fish or the egg-laden mops, and rear separately, starting them off on newly hatched brine shrimp. A drop of Methylene blue to stop the eggs from developing fungus is optional. 


The subject of culling fish is taboo, but it needs to be discussed if breeding Ryukin. The process of culling, is to remove or thin out batches of fry, keeping only the best ones for further raising. You don’t have to do anything, although the Ryukin you bought will have been the survivor of many culls since just a few days after it hatched. To cull can also mean to kill, although again, only do what you are comfortable with, and if you want to raise and care for every single baby fish, you can do.

Culling occurs because Ryukin look a certain way, and goldfish genetics want to revert the fish to wild type. This means that not all Ryukin fry will grow up to look like Ryukin. Some will have single, not double tails, others, pronounced deformities such as bent spines, but the biggest reason for culling is sheer numbers. A single mature Ryukin may produce hundreds, if not thousands of eggs in a single spawn. As hatched fry they will need increasing amounts of food, fed over a 24 hour period, and the fry will need more space, and clean, filtered water as they grow. 

Most simply cannot afford to buy the amounts of brine shrimp eggs necessary for thousands of fry, nor do they want to get up every four hours throughout the night to feed the fry. By cutting numbers right down to hundreds, then tens, as soon as they can, means more room for the fry to grow and more brine shrimp nauplii per fish when its added to the fry tank, which also means the food lasts longer, and sustains the fish for longer between feeds. 

I’ve bred goldfish many times, and always tried not to cull any, but the result is stunted fry that become months and ultimately years behind on the size that they should at for their age. This is because I can’t provide enough space or food for 1000 goldfish to grow. Despite trying…and let along 1000 adult fancy goldfish. 


Ryukin will mix with their own kind or other fancy varieties like fantails, oranda, telescope eyes and ranchu. Being big, strong fish, they wouldn’t even be muscled out at feeding time if mixed with single tail varieties like shubunkin, common goldfish and comets.

Weather loach could be added to tanks containing large fish if non-goldfish were required, although adult Ryukin would eat danios and white cloud mountain minnows, and any of the temperate shrimp varieties. Best to keep to goldfish only, or even Ryukin only, with a contemporary hardscape arrangement and five same size, same colour Ryukin making for a very impactful visual display. 


The biggest problem you are likely to encounter with Ryukin is floaty fish. This I put down to that short fat body and deformed swim bladder. Choose “balanced” fish with a medium-sized tail and a not too squashed body shape. Feed sinking foods too. 

Often “swim bladder” is not a disease at all, and I find limited success by administering salt and/or a specific swim bladder disease treatment.

Next is disease in general. Bred for looks not for hardiness, Ryukin don’t like prolonged UK winters outside and are susceptible to lots of parasites you can’t see, like Flukes. I routinely treat for Flukes, have lost fish to Flukes when I haven’t medicated for them, and ideally, you should find a friend with a microscope who knows how to take a skin scrape, and what they’re looking for. 

Then there’s water quality. Large fish plus frequent feeding equals ammonia, and if ammonia isn’t at zero at all times these fish will get ill. Blood in the fins of white fish is a common indicator that something isn’t right. Constant low levels of ammonia and/or nitrite are common in fancy goldfish tanks. They’re big and messy.  


Get into fancy goldfish and sooner or later you will find out about goldfish clubs. There are several spanning the UK and they have their own standard for what a Ryukin should look like. Breed and raise fish that most adhere to that illustrated standard, and you could be a winner. At shows, you will find other enthusiasts, tips on showing fish and breeding them to club standards, along with lots of associated food and equipment to buy, and often, fish for sale too. 

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Jeremy Gay

Author of three fishkeeping books and lifelong fishkeeper. Experience includes editor of Practical Fishkeeping magazine, editor of Pet Product Marketing magazine, multi award- winning livestock manager and aquatic store manager.