breeds Tosakin Goldfish

Tosakin Goldfish Care, Characteristics, and Tank Setup

Tosakin goldfish are rarely seen, and I in fact struggled to even find many photos to share here because of it. Learn all about this rare goldfish type here.

By Michelle Jo (Own work), CC0, via Wikimedia Commons

Tosakin are one of the rarest varieties of goldfish and one of the most striking. What makes them so distinctive is they’re the only goldfish to have an undivided double tail.

While they’re somewhat rare even in their native Japan, they’re almost unheard of in North America and Europe. Therefore, you’ll need to find a reputable breeder – and be willing to shell out a fair amount of money per fish – if you want to keep tosakin.

However, if you’re still keen on learning more about tosakin goldfish – and how to successfully keep them – read on.


As mentioned above, the most distinctive feature of tosakin goldfish is their undivided double caudal fin. From above, this appears as a full semi-circle and looks entirely different from any other goldfish tail.

Their bodies are short, squat and egg-shaped, but with pointed heads. The depth of the body should be approximately 60 percent of the length. The tail should be at least 75 percent of the length of the body, with scalloped edges and a wavy, twisted appearance to the upper lobes.

Tosakin Colors and Variations

Tosakin goldfish can be found in a range of colors: orange, orange and white, red, red and white, black, yellow, and calico. However, of these colors, orange and orange and white are by far the most common.

There’s only one known variation of the tosakin: the telescope eye tosakin. This fish is exactly like a regular tosakin, except the eyes are “globed” or on stalks like a telescope eye goldfish. Telescope eye tosakins are even rarer than the standard variety.

How Big Do Tosakin Goldfish Get?

Tosakins usually measure between 4 and 6 inches but can grow as large as 8 inches.

How Old Can They Get?

The average lifespan of a tosakin goldfish is roughly 10 to 15 years. However, they have been known to live for up to 20 years with exceptional care.

If you’re going to keep goldfish, make sure you’re prepared to look after them for the next couple of decades.


The tosakin goldfish has a fascinating origin story.

These fish were developed in Japan in the early 1800s, and first recorded as a distinctive type in 1845. They were mostly kept and bred in the Kochi prefecture, which was then known as “Tosa,” hence their name.

It’s believed they were bred by low-level Samurai, by either crossing the ryukin with the osakarachu goldfish or as a result of a natural mutation of the ryukin.

But that’s not the most notable part of the story: after World War II tosakin were thought to be completely extinct. They were still only really kept in the Kochi prefecture, which had been bombed extensively.

Miraculously, a man named Hiroe Tamura, a hobbyist breeder who’d lost all his fish during the war, spotted six living in a restaurant and managed to trade them with the restaurant owners for a bottle of sweet potato vodka. He started a breeding program and so all tosakin alive today are descended from these six fish.

Easy to Keep in an Aquarium?

Tosakins aren’t quite as hardy as many other goldfish, so they’re not great starter fish – although their price would probably prevent first-time fish keepers from buying them, anyway.

While they’re still easier to keep than tropical or marine fish, they’re more challenging to keep than your average fancy goldfish.

Video: Tosakin Goldfish in Action

Watch the video below to see what a tosakin’s distinctive tail looks like in the flesh.

Tosakin Goldfish Care Requirements

You’ll need to consider several factors when caring for your tosakin.

Since these goldfish have delicate tails, make sure you don’t house them with any sharp ornaments or plastic plants that could snag or damage their tail.

Their undivided double tail also impedes their swimming ability, meaning they’re not strong or fast swimmers. As such, avoid filtration that creates any kind of current, as this will make their swimming worse.

You’ll also need to be careful what other fish you house them with, as their slow swimming means they’re easily out-competed for food.


Like all goldfish, tosakins are omnivores, meaning they eat both animals and plants. They need a varied, balanced diet to stay in tip-top condition.

The central part of their diet should consist of a high-quality flake or pellet designed specifically for fancy goldfish. Supplement this with a range of fresh, frozen and freeze-dried foods, including blood works, mosquito larvae, shelled green peas, and blueberries (though always make sure these foods are cut to an appropriate size for your fish).

As with other egg-shaped goldfish, tosakins can have swim bladder issues – causing them to float or sink in their tank – if overfed or given foods that can cause a blockage in their digestive tract.

Therefore, be sure to soak any pellets or other dried foods before giving them to your fish, and feed two or three small meals a day instead of a single large one.

Setting up Their Tank

Technically, the tosakin is a pond fish, as their impressive fan-like tails are meant to be viewed from above. However, there’s no reason why you can’t keep them in an aquarium, as long as you don’t mind the fact you won’t be looking at them from the best angle.

If you do choose to keep them in an aquarium, follow the advice below to get the best set-up for your tosakin.

Size and Shape of Tank?

Traditionally, tosakins have been kept in large, shallow earthenware bowls. While we wouldn’t recommend this, most tosakin keepers suggest housing them in water that’s less than 8 inches deep.

To make sure they have enough room to swim, the width of their tank should be at least six times the full length of their body. Since they can reach up to 8 inches long, this means their aquarium should be 48 inches (or 4 feet) wide to accommodate their full adult size.

While you could start with a smaller tank and size up as they grow, we’d consider this to be a false economy.

Is a Filter Needed?

Goldfish produce a lot of waste, so therefore, goldfish need a powerful filter.

As mentioned above, tosakins aren’t good swimmers, so their water should be as still as possible. This means you should avoid any type of filter that creates a strong current.

Do they need Substrate?

Tosakin goldfish don’t need to have a substrate, but many fish keepers prefer the look of it, rather than having a bare-bottomed tank.

If you choose to use substrate, either use fine sand or smooth medium to large gravel. Gravel should have no sharp edges, so it won’t damage your tosakin’s delicate tail and should be too large for you fish to swallow.

Lighting Requirements

If you keep your tosakin goldfish in a well-lit room, artificial lighting isn’t essential. It’s worth noting, however, you should never keep an aquarium in direct sunlight, as it can cause the water temperature to rise to uncomfortable levels, plus it may result in an algae bloom.

Some goldfish keepers like to use artificial lighting anyway, as it makes the tank look brighter and (arguably) more attractive.

Should you choose to use artificial lighting, keep it on for 12 to 16 hours a day and off for 8 to 12 hours a day, to replicate a natural day/night pattern.

If you plan to keep beneficial live plants, lighting is essential to keep them alive, but you need to follow some specific requirements.

What temp Should Their Water Be?

Tosakins can tolerate slightly warmer temperatures than other goldfish and can be kept in water anywhere between 59 and 86 degrees Fahrenheit.

Though it’s not essential if you’re aiming for the lower end of that spectrum, you might choose to use a water heater to keep a more consistent temperature.

Preferred Tank Mates

Since they’re poor swimmers, you need to be careful what other fish you house with your tosakin. They’re slow, placid fish that are easily out-competed for food, which could lead to malnutrition and even starvation.

The best tank mates for tosakin goldfish are other tosakins, but they can also be kept with slow-moving goldfish that have a handicap which makes aggressively competing for food impossible. For example, the celestial eye or the bubble eye goldfish.

Final Thoughts

While tosakins are beautiful goldfish, they’re not the easiest to look after or the cheapest to get hold of, so you really must be dedicated to this goldfish variety if you’re going to keep them.

However, they are a beautiful fish, and somewhat rare compared to many other types of goldfish, so are very rewarding.

Jeremy is the chief editor of this site. A fish keeping enthusiast for more than 2 decades, he founded this site so he can share his knowledge with others, to aid in enjoyment of fish keeping, and to get as much fun out of the hobby as he does.

Leave a Comment