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Tosakin Goldfish: Pictures, Size, Care, Tank Setup & More

Sarah Psaradelis

By Sarah Psaradelis

Tosakin or curly fantail goldfish_Sad Agus_shutterstock

The beautiful and rare Tosakin Goldfish is a fancy variety that was originally developed in Japan. Tosakin Goldfish are sometimes referred to as Curly Fantail Goldfish, and they have an undivided twin tail that is meant to be viewed from above. Although they are not as delicate as some other fancy goldfish varieties, the Tosakin is still recommended for more experienced goldfish keepers.

Caring for a Tosakin Goldfish is a rewarding experience, and they are a great addition to goldfish collections.

Size: Up to 8 inches long
Lifespan: 10–15 years
Similar Breeds: Fantail, Ryukin, and Ranchu
Suitable for: Experienced goldfish keepers
Temperament: Slow-moving, friendly, peaceful, and social

Tosakin Goldfish are believed to be a mix between the Ryukin and an Osaka Ranchu Goldfish. However, Tosakin Goldfish could be the result of a genetic mutation from Ryukin Goldfish. They are striking Japanese goldfish with compact egg-shaped bodies, curly tails, and available in a range of colors. Their unusual tail is what makes them so rare and highly sought out, although their tail does affect their aquarium setup and swimming behaviors.

This article will guide you through Tosakin’s fascinating behavior, stunning appearance, and important care requirements.

Tosakin Goldfish Characteristics

Ease of Care

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How Much Do Tosakin Goldfish Cost?

Tosakin Goldfish originated in Japan. They were likely developed in 1868 and were thought to be extinct after the natural disasters and World War Two that devastated the Kochi Prefecture of Japan. However, goldfish breeders have been dedicating a lot of time to keep this goldfish variety alive and developed according to their breed standards.

Tosakin Goldfish are somewhat rare outside of Japan, but they have gained popularity in recent years. They are not widely available like most ornamental goldfish, and it is difficult to find true Tosakin Goldfish in the United States and many other parts of the world. You are unlikely to find Tosakin Goldfish for sale in most pet stores and they are primarily sold by reputable goldfish breeders.

The Tosakin Goldfish’s rarity means that they are pricey goldfish, sometimes costing a few hundred dollars. Young Tosakin Goldfish are usually priced between $80 to $200 per fish, but high-quality Tosakin adults can cost up to $500.

However, you do not need to travel to Japan to find a Tosakin Goldfish for sale by a breeder. Tosakin Goldfish can be purchased online from Japanese goldfish breeders, usually at a fair price depending on the goldfish’s size and quality.

top view of two Tosakin Goldfish in white background
Image Credit: Pavaphon Supanantananont, Shutterstock

Sociability of the Tosakin Goldfish

Do These Fish Make Good Pets?👪

Tosakin Goldfish can be good pets for more experienced goldfish keepers who enjoy looking after rare fancy goldfish. They need slightly different aquarium setups because of their modified caudal (tail) fins which make them poor swimmers. You cannot keep Tosakins in just any goldfish tank, and you need to create an ideal environment for them. Very large and shallow bowls were traditionally used to house Tosakin Goldfish in the first few months of their life. They were later moved to standard glass fish tanks for viewing purposes.

Shallow tanks, indoor ponds, or wading pools are now used to house Tosakin Goldfish through each stage of their life. They should not be placed in aquariums with a current as they are not the best swimmers. Most Tosakin Goldfish are slow and prefer to float around the midsection of an aquarium. When they swim, Tosakins can tire easily and need to rest frequently.

Many Tosakin Goldfish enthusiasts opt for shallow ponds or wading pools rather than glass fish tanks. This is because the Tosakins tail was developed to be viewed from above rather than the side. Their aquariums are usually placed low on the ground for easy viewing, and decorated with a sponge filter, live plants, and no substrate.

If you decide to care for a Tosakin Goldfish, keep in mind that they are sensitive to water quality and environmental stressors. They do not deal with stress well and are not very resilient. They require a quality diet and proper living conditions with well-maintained water.

Does This Fish Make a Good Tankmate?

Tosakin Goldfish make good tankmates for other slow-moving fancy goldfish. They are social and benefit from having other goldfish as tankmates. However, they should not be kept with streamlined goldfish varieties such as common, Comet, or Shubunkin Goldfish. They are better paired with Ranchu, Ryukins, Orandas, Pearlscale, or Telescope-eye goldfish similar in size. Tosakin Goldfish are not the best choice for the more fast-moving goldfish varieties as they are at risk of being bullied or starved by those goldfish. Tosakins are poor swimmers and take a while to find food, which streamlined goldfish will eat first.

You want to avoid keeping Tosakins in the same tank as other fish species, even if they are peaceful and social. Tosakins are only compatible with other fancy goldfish and adult mystery snails.

tank full of tosakin goldfish
Image Credit: Fajar Tri Amboro, Shutterstock

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Care Guide & Tank Set Up

Tosakin Goldfish require a shallow aquarium with around 20 gallons of water. An additional 10 gallons is required if you keep Tosakins with other goldfish as recommended. Tosakins are not a good choice for outdoor ponds. They are not hardy enough to survive constant fluctuating temperatures and harsh weather conditions.

Here’s everything you need to know about a Tosakins tank setup and water conditions.

Water Quality, pH & Temperature

Tosakins need good water quality to stay healthy and active. They are sensitive to sudden changes in water chemistry, so their water quality needs to be closely monitored. Tosakins do not need a heater in their aquarium unless the water temperature is unstable or regularly drops below 60 degrees Fahrenheit.

Their aquarium needs to be properly cycled before they are placed inside. Tosakin Goldfish require 0 ppm ammonia and nitrite in their water. They are easily distressed by slight traces of ammonia and nitrite in their water and can become severely ill. The nitrate level should stay below 15 ppm, and you can use a liquid testing kit to monitor the levels.

Ideal Water Parameters for Tosakin Goldfish:
  • Temperature: 65° to 75° Fahrenheit (18° to 23° Celsius)
  • pH: 0 to 8.0
  • Water hardness: 80 to 160 ppm
  • Ammonia level: 0 ppm
  • Nitrate level: 0 ppm
  • Nitrate level: Below 15 ppm


If you choose to use a substrate in your Tosakin Goldfish’s aquarium, sandy substrates are preferred. Quartz and fine gravel substrates are safe too. You do not necessarily need to keep a substrate in their aquarium, and most Tosakin Goldfish are fine with a bare-bottom tank.

group of tosakin goldfish in the tank
Image Credit: Fajar Tri Amboro, Shutterstock


Both fake and live plants can be used to decorate your Tosakins aquarium. They help make your Tosakin feel more secure in their environment rather than being left out in the open. Any fake plants in their aquarium should have smooth surfaces since ragged edges can catch onto their fins and cause damage. Live plants like java fern, java moss, hornwort, water sprite, and elodea can be grown in a Tosakin Goldfish’s aquarium. You can either plant them in a sinking pot or directly into the substrate.


Tosakin Goldfish need around 6 to 10 hours of light per day. This can be from natural lighting or overhead lighting. All lighting should be turned off at night to allow your Tosakin Goldfish to rest. You ideally want to avoid keeping the lights on for more than 10 hours at a time to limit algae growth. Tosakin Goldfish do not need very bright lights as they can be stressful and reflect harshly in their eyes.


Since Tosakin Goldfish have unique caudal fins, they are very poor swimmers and should never be kept in an aquarium with a water current. Surface agitation from a filter or bubbler system is recommended to help keep their water aerated. However, the filter should not produce a current even if it is mild. Tosakin Goldfish are not good swimmers because of their unique caudal fins and will get pushed around in the water if there is a current.

Sponge or under-gravel filters are recommended for Tosakin Goldfish since they do not create much of a current and help to keep the water clean and oxygenated.

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Things to Know When Owning a Tosakin Goldfish

Food & Diet Requirements🥫

Feeding a Tosakin is relatively straightforward, and their diet is no different than other ornamental goldfish. Tosakins are omnivores and should eat commercial goldfish food that contains a blend of plant and animal-based ingredients.

A quality goldfish flake or pellet is suitable for Tosakin Goldfish, with small pellets being preferred. Flakes usually dissolve quickly in the water and lose their nutrients, so a pellet that slowly dissolves is better. It is better to choose pellets that sink to prevent your Tosakin from gulping air as they eat.

Dietary supplements are optional but can be beneficial if you want to keep your Tosakin healthy. Bloodworms, daphnia, baby brine shrimp, and algae wafers can be fed to Tosakins three times a week. You can find those foods in most pet stores, and they should be marketed as aquarium fish food.

Size & Growth Rate📏

In comparison to many other goldfish varieties, the Tosakin is relatively small. They usually grow between 6 to 8 inches long and carry most of their weight in their round and compact bellies. Tosakin Goldfish are slow-growing fish that take up to 4 years to reach 6 inches in size. You can speed up their growth rate by feeding them a high-quality diet and keeping them in a proper environment and spacious aquarium.

Tosakin goldfish_Pavaphon Supanantananont_shutterstock
Image credit: Pavaphon Supanantananont, Shutterstock


Tosakins are a rare variety of fancy goldfish that resemble Ryukin and Ranchu Goldfish. They have deep-set bodies with rounded abdomens typically seen in fancy goldfish. They have a divided double-tail that fans out horizontally rather than vertically like most goldfish. Their tail fin does not look like much until you view it from above. They have either long or short fins, with long fins being the most spectacular. They have a slightly rounded dorsal fin along with a pair of pectoral fins that they use to swim.

You can find Tosakin Goldfish in brilliant colors like yellow, red, orange, white, black, brown, and blue. Tosakin Goldfish have metallic scales which make them appear shiny and intensely colored. It is possible to find Tosakin Goldfish with calico markings, although it is rare.

Lifespan and Health Conditions🏥

When cared for properly, most Tosakin Goldfish can live between 10 to 15 years. Some Tosakin Goldfish will live longer than others depending on their genetics, health, and living conditions. Unfortunately, certain health conditions can cause your Tosakin Goldfish to live a shorter expected lifespan.

Minor Conditions
  • Cloudy eye
  • Neurofibromas
Serious Conditions
  • Swim bladder problems
  • White spot disease or ich
  • Bacterial or fungal infections
  • Gill flukes
  • Velvet
  • Ammonia poisoning
  • Ulcers
  • Internal tumors
  • Fin rot

Male vs Female

There are subtle differences between male and female Tosakin Goldfish that are mostly noticeable during the breeding season.

Male Tosakin Goldfish
  • Longer and more flowy fins
  • Chasing behavior during the spawning season
  • Small and concaved vent
  • Breeding tubercles/stars on gills
Female Tosakin Goldfish
  • Larger and rounder abdomen
  • Lopsided belly when carrying eggs
  • Rounder and convex vent
  • Shorter fins

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3 Little-Known Facts About Tosakin Goldfish

1. The Tosakin Goldfish has a horizontal caudal (tail) fin that is unique to the variety.

2. Tosakin Goldfish are very rare and nearly became extinct in the 1900s.

3. The best way to appreciate the Tosakin’s tail fin is to keep them in aquaria which allows you to view them from above. This is how they have been traditionally kept for decades.


Final Thoughts

Goldfish can be found in all sorts of shapes and sizes, and the Tosakin is one of the more unique varieties of fancy goldfish. Tosakin Goldfish have a distinctive divided caudal fin that looks striking in aquariums. They have been around for years, although they are recently gaining popularity as pets. Tosakin Goldfish are not as widely available as other goldfish, so you can expect to pay a couple of hundred dollars for an adult.

They are worth the price with their fascinating behaviors and unusual appearance, but experienced goldfish keepers may find them easier to care for.

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Featured Image Credit: Sad Agus, Shutterstock

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