Comet goldfish care guide

Comet is one of artificially bred ornamental tank goldfish, which has a classical elongated body (not an oviform shaped like all other representatives of this kind have) and a long tail.

Habitat in the wild

Just like all representatives of this family, comet goldfish descended from a common carp and it can’t be encountered in the wild.

According to one sources, this breed is considered to be bred in the USA at the beginning of 1880 by Hugo Mulertt. However, in the book «Aquaria» published in 1898 it is said that comet is a Japanese fish and it got to America in 1872. Mulertt himself in his book published in 1883 also says that the fish originated from Japan.

As for Japanese, they make no pretense to the palm of victory at all as those who were the first to get this breed. It is quite possible that Mulertt bred American variety of the breed using the species that were obtained in Japan.

Nowadays it is unknown what comet goldfish was used to get the offspring in the USA. Fishes that have description similar to the one of goldfish are referred as those that were obtained in Macao in 1834.

Scientific NameCarassius auratus auratus
Common NamesComet goldfish; Comet fish
Range and habitatNo
Sizeup to 28 cm (11 in)
Lifespan15-20 years
Ease of keepingEasy
Minimum tank size44 gallons
Temperature20-23 °C (68-73 °F)
Water hardness5-20 dGH


This breed of goldfish unlike all its relatives has elongated body. Distinctive feature of this goldfish breed is its long tail, that has to be equal at least ¾ of the body length.

The comet goldfish tail isn’t claw-ended, it has two rays and forms kind of ‘tick mark’. Quite often such a long tail is accompanied with long pectoral and abdominal fins, that hang down like ribbons.

This species body has to be elongated. Length of the body is up to 28 cm (11 in), this is quite a large fish. Comet is a long-liver, provided with good tank conditions it can live from 12 to 20 years.

Difficulties in keeping

The comet goldfish is quite undemanding, but large, active and it prefers cool water. Due to this it is quite problematic to keep it in a tank, therefore it is preferable to keep it in ponds in the open air.

Care and keeping in a tank

Comet is a very enduring goldfish, it grows quickly and it is very energetic. They prefer bright natural lighting. As for the keeping in a tank peculiarities, we should mention that you have to secure the comet goldfish from damaging its long tail and especially its body.

Stones with sharp edges and snags with knots mustn’t be put into the tank.

Tank size

Large size of the comet goldfish makes it more suitable for keeping in ponds, than in tanks. Fish requires a large volume tank. However, still you can keep a couple of adult fishes in a tank of 200 liters (44 gallons).

You should give preference to long tanks, not high ones.

In average comet goldfish grows up to 28 cm (11 in) long, its size also depends on the size of the pond or tank where it lives. Another thing is – the more you feed fish, the larger it grows.

Water parameters

A tank with comets inside should be covered. Water hardness and pH are not important. However, preferable water hardness is 8 – 25°, acidity 6 – 8. Weekly water renew up to 30% of the total water amount is a must.

Recommended water temperature is 18 – 26 °C (64-79 °F), but it’s better be 20 – 23°C (68-73 °F). The comet goldfish can deal with temperature variations, but the main thing is that there shouldn’t be abrupt temperature changes.

In acid water of poor quality the comet goldfish may have torn fin edges with white discoloration – you should renew the water as often as possible. In an hour or two after the water renew these manifestations magically disappear (this doesn’t concern fungous and bacterial diseases).

It is desirable to get a compressor for additional water blowdown with air (comet is sensitive to lack of oxygen in the water) and a good filter is required for water filtration. It should have high capacity – not less than 3 volumes of the tank in an hour, especially if there is not one fish in the tank.

Tank decor

This comet goldfish likes digging tank bottom substrate looking for some additional food and thus makes the water muddy.

Soft leaved tank plants are quickly eaten by the fish or their leaves become soiled with floating rubbish. That’s why it is recommended to put into the tank coarse leaved plants with strong roots that don’t require water heating.

Put them into flower pots, not into the bottom substrate and protect their roots with large pebbles. Fish digs tank bottom all the time and it may pull out tank plants.

The bottom substrate pebbles should be smooth and without sharp edges. So, it’s better to use pebbles or sand as tank bottom substrate. It should be large, about 3-5 mm in diameter. It’ll be good to cover the tank bottom with pebbles and make the scape look better by putting large round shaped stones as well.


Comet is prone to obesity, so you shouldn’t overfeed the comet goldfish. The food portion should be enough for the fish to eat for a minute-two or for 5 minutes the longest.

The food leftovers have to be removed from the tank at once, since they get spoiled very fast and can poison the tank water even during a night.

It’s better to feed the comet goldfish with small portions of food several times a day, but the fish should eat up the food completely.

The amount of food the fish consumes everyday shouldn’t exceed 3% of its weigh. If the fish after feeding starts to swim belly up or behaves strangely, swims to the water surface or hangs upside down – these are the signs that the comet goldfish was overfed.

The adult fish is fed twice a day – early in the morning and in the evening. It requires less protein, but more carbonhydrates in its diet. That’s why it’s better to feed it with special food for goldfish. Except special nutrients with large amount of carbonhydrates this food contains natural supplements that improve yellow, orange and red colors of the comet goldfish body coloring.

This goldfish eagerly feeds on soft leaved plants. To avoid this the fish food should contain large amount of vegetable component and you can feed it with some vegetable food additionally.

It is important to keep in mind, that when feeding the comet goldfish with dry food of any type, you should give it in small portions several times a day, because when getting into the water it swells on wetting, gets larger and may cause digestive disorders and the fish death as a result.

You can put dry food into water for some time before giving it to the fish (10 seconds for flakes, 20-30 seconds for pellets) and only then feed fish.

Tank mates

The comet goldfish is a schooling one. It is very active, quite more active than most of the goldfish kinds. It’s not desirable to keep comet with large fishes, that tend to demonstrate aggressive behavior (oscar fish, green terror, flowerhorn).

As for small fishes and juveniles – you also can’t keep them together, since it will eat them. Therefore, it is better to keep the fish with other goldfish kinds (shubunkin) or with calm tempered fish species.

Gender differences: male vs female

It is quite difficult to tell between the comet goldfish male and female. Though, the male fish ready to spawn has some distinctive features: notched first ray of front pair of its pectoral fins and some small outgrowths (of semolina grain size) on its grill covers.

The female fish that is reproductive and ready to spawn has fat belly full of eggs.