Cold Water Fish


  • Scientific name: Carassius auratus
  • Common Name: Shubunkin Fish, Comet Fish, Harlequin Goldfish
  • Aquarium size: 150 to 200 liters
  • Temperament: Calm
  • Temperature: 16ºC to 20ºC
  • pH: 7
  • Diet: Omnivores
  • Length: Between 15 and 35 centimeters, maybe more


The Shubunkin is a variety of Carassius auratus , Goldfish, Redfish or Cometfish, as the common names accumulate, due to the great popularity of this fish.
Therefore, it is a fish of the Cyprinidae family , it is a cold-water fish, which would be perfect living in a large aquarium, and also in a pond outside.
Like the different varieties of Goldfish: Telescope Fish , Lion’s Head, etc., the Shubunkin is a variety of Carassius auratus obtained through the crossing and selection of specimens.
Sometimes the Shubunkin is confused with the Calico, because their coloration is similar.
The first specimens have their origin in Asia (1,900), where they began to breed and select. It seems that he later traveled to the United Kingdom, finally arriving in the United States.


There are various details of the Shubunkin’s morphology that make them so special and desired.
In the first place, their scales are very thin and transparent, giving the feeling of completely lacking them, although they do.
The other distinguishing feature that makes it such a special and desired fish is its coloring.
It is common to find specimens with a bluish base, dotted with black spots and red patches . Their coloring and spots are so chaotic that they seem to have been painted by a child … it is difficult for us to find two identical fish, even similar ones would be difficult.
It seems that in principle the base was red, dotted with other colors, with black being the main one. As I mentioned, with the multiple crosses that have occurred, the usual thing right now is to find Shubunkin with a bluish base, mixed with other colors.
They have an elongated, slender, hydrodynamic body, very similar to the common Goldfish. Fins short and rounded, somewhat flattened laterally: in all Shubunkin the tail fin divided into two lobes.

Sexual dimorphism

There are several ways to differentiate the male Shubunkin from the female:

  • Females have a slight outward bulge at their anal opening, while in males it is inward.
  • If the temperature of the aquarium or pond rises, we will be able to appreciate how in females the belly seems more bulky. In males, small white granites are seen on the gill covers and pectoral fins, called reproductive tubers.
  • We may not have been able to differentiate them before mating, from that moment on we will have it very easy.
    The males are the ones who chase the females, hitting them with their heads in the abdomen.

Shubunkin varieties

Although some varieties are difficult to find for sale, these are the most popular originating from the Shubunkin fish:

Shubunkin london

It is the most popular and easiest variety to find. It can reach 35 centimeters or more, and morphologically it is very similar to the common Carassius auratus.
The coloration is mottled, with the fins blackish, while the tail fins are striped.

Shubunkin Bristol

They are very similar to the previous ones, except that morphologically, their tail fin is longer, wider and their coloration is more striped.
The tail fin (divided into two lobes) in this variety is rounded and somewhat more upright. They are somewhat more stylized than most Shubunkin.

American Shubunkin

Very similar to the dorsal-fin kite, with long, pointed fins. As a curiosity, it only has a single anal fin.
Its coloration is mottled.

Shubunkin kite

Its body is slim, with highly developed fins. The fins are usually colored black or brown.

Distribution and habitat

The origin of the Shubunkin is that of the Carassius auratus: East Asia.
Where it gained the most popularity, without any doubt was China, from where they left for different countries in the world after starting their selection and crossing.
Its natural habitat is the rivers of cold water and slow course. They are the ideal fish to keep in an outdoor pond, as they are able to withstand the low temperatures outside.

Aquarium conditions

They need a good size aquarium, ideally 100 liters and up. As a rule it is said that they need about 40 liters of aquarium per specimen.
The water conditions must move within the following parameters:

  • Temperature between 16ºC and 20ºC
  • pH 7 to 7.5
  • gH between 10º and 15º

They are not too demanding fish, on the contrary, they are capable of resisting water qualities and temperatures very different from those that I have marked, although these are the most suitable for a perfect state of health.
Inside the aquarium it is recommended that the plants are resistant, with hard leaves: Anubias , Java Fern
It is recommended that the water be well aerated, so adding a bubble diffuser can be a great decision.
The bottom of the aquarium is preferably gravel without edges and not very thick. They perfectly allow us to add rounded stones and logs to decorate.

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They are omnivorous fish . We can use a diet with good quality dry food , supplemented with vegetables and live food, such as brine shrimp.
The smallest specimens can be fed with scales, while the largest ones will prefer food in granules or sticks.

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Behavior and compatibility

They are sociable fish. We will achieve the best results with a small school, which will depend on the size of our aquarium … 5 or 6 specimens would be fine.

Shubunkin Compatible Fish

They can live with other cold-water fish, provided they are not too small, nor should they be mixed with fingerlings, as they could become part of their diet.
Although in theory they can share space with other Goldfish , you have to think that some varieties are very slow in their movements and when it comes to eating, while the Shubunkin is a very fast Goldfish.


They reproduce easily. It is not uncommon for, if we have them in a pond, to realize that the number of fish has increased without having to do anything to achieve it.
The specimens are sexually mature with 8 to 10 months. Some specialized pages do not recommend that they begin to reproduce so small, that it is better that they reach a larger size … I do not know what the fish will think, but if they are free I imagine that they will reproduce when they have the opportunity …
The reproduction coincides with the summer season, when the water is between 18ºC and 22ºC.
These conditions can be reproduced using a mating aquarium, which must have at least 80 liters, in which the temperature has to be in the environment of 22ºC.
We will place a female and two or three males, to improve the reproduction options.
If all goes according to plan, the courtship will begin. The males will harass the female, giving her blows to the abdomen to expel the eggs.
Once expelled, the males will fertilize them with their sperm.
The eggs will stick to any nearby surface: plants, rocks … Once the laying is finished, it is better to remove the adults from the aquarium so that they do not eat the eggs. Farrowing pens can be used to keep the eggs safe from adults, filters, and other potential hazards.
The incubation period is about 72 hours. From that moment the fry will begin to swim freely. We’ll feed them brine shrimp nauplii.

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