The Complete Guide to Comet Goldfish Care: From Setup to Maintenance

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. Comet goldfish are a specific variety within the goldfish species, characterized by their elongated body shape and long, flowing tails. They are often referred to as “comets” due to their swift and agile swimming abilities. Comet goldfish are highly popular among fish enthusiasts for their striking colors and graceful appearance.

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. Comet goldfish (Carassius auratus) belong to the Cyprinidae family, commonly known as the carp family. The Cyprinidae family is one of the largest fish families, consisting of numerous species of freshwater fish found worldwide. Some other popular members of the Cyprinidae family include koi, common goldfish, rosy barbs, danios, and minnows.

Within the Cyprinidae family, goldfish and their various varieties have been selectively bred over centuries to exhibit different characteristics, including body shape, coloration, and finnage. Each goldfish variety, including the comet goldfish, is a result of specific breeding efforts to create desired traits.

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.



This breed of goldfish unlike all its relatives has elongated streamlined body shape. Their body is elongated, slender, and slightly flattened laterally. The body tapers towards the tail, giving them a torpedo-like form. Their body is covered in small, overlapping scales that offer protection and contribute to their shimmering appearance.


One of the distinctive features of comet goldfish is their long and flowing tail fin, that has to be equal at least ¾ of the body length. The tail is deeply forked and resembles a comet, hence the name “comet goldfish.” The tail can extend to impressive lengths and adds to their graceful appearance. In addition to the tail fin, comet goldfish have dorsal fins, pectoral fins, pelvic fins, and anal fins. Quite often such a long tail is accompanied with long pectoral and abdominal fins, that hang down like ribbons. These fins are generally proportional to their body size and help with stability, maneuvering, and propulsion.


The most common coloration of comet goldfish is a bright orange or red hue. However, they can also exhibit variations, including paler shades, yellow, and white. The coloration is often vibrant and can intensify with proper care and diet.

Comet goldfish have protruding, round eyes. Their eyes are located on the sides of their head, allowing for a wide field of vision. The eyes can be black or metallic in color, complementing their overall appearance.


How big do comet goldfish get?

Comet goldfish can grow relatively large compared to other goldfish varieties. In ideal conditions, comet goldfish can reach lengths of 12 to 14 inches (30 to 35 cm) or even larger. However, their growth potential largely depends on several factors, including genetics, diet, water quality, and the size of their environment.


How long do comet goldfish live?

Comet goldfish (Carassius auratus) have the potential to live for a relatively long time when provided with proper care and a suitable environment. On average, comet goldfish can live for 10 to 15 years, but with optimal conditions, they can live even longer.

Factors such as genetics, water quality, diet, and overall care play significant roles in determining the lifespan of comet goldfish. Providing them with a well-maintained aquarium or pond, regular water quality monitoring and maintenance, a nutritious diet, and a stress-free environment can contribute to their longevity.

It’s important to note that individual comet goldfish may vary in lifespan, and some can live beyond 15 years with excellent care. Additionally, certain environmental factors or health issues can affect the lifespan of goldfish. Keeping an eye on their overall health, addressing any potential health concerns promptly, and providing consistent care can help maximize their lifespan and ensure they live a healthy and fulfilling life.

Common NameComet Goldfish, meteor goldfish
Scientific NameCarassius auratus
Body ShapeStreamlined with an elongated body and a forked tail
SizeCan grow up to 12-14 inches (30-35 cm)
Lifespan10-15 years or longer with proper care
ColorationTypically orange or red, but various color variations exist
TemperamentGenerally peaceful and sociable
Tank/pond sizeMinimum 30 gallons for a single fish; larger for multiples
Water ParameterspH: 7.0-8.4, Temperature: 65-75°F (18-24°C)
DietOmnivorous, feeds on pellets/flakes, vegetables, and treats
CompatibilityCompatible with other goldfish varieties and larger fish
HabitatKept in aquariums or outdoor ponds
Water QualityRequires good filtration and regular water changes
EnrichmentBenefits from hiding places, plants, and decor in the tank
Special ConsiderationsCan grow large, produce significant waste, need space to swim

Comet vs common goldfish

Comet goldfish and common goldfish are both popular varieties within the goldfish species. While they share some similarities, there are notable differences between comet and common goldfish:

  1. Body Shape: One of the key differences between the two varieties is their body shape. Comet goldfish have a more streamlined and elongated body, resembling a torpedo. In contrast, common goldfish have a more rounded and egg-shaped body.
  2. Tail Shape: The tail shape is another distinguishing feature. Comet goldfish have a deeply forked tail, resembling a comet or a double crescent shape. Common goldfish, on the other hand, have a more rounded tail without the distinct fork.
  3. Size: In terms of size, comet goldfish tend to be smaller compared to common goldfish. Comets typically grow to lengths of 12 to 14 inches (30 to 35 cm), while common goldfish can grow larger, reaching lengths of 10 to 18 inches (25 to 45 cm) or even more.
  4. Coloration: Both comet and common goldfish exhibit a wide range of color variations. However, comet goldfish are more commonly found in shades of red or orange, while common goldfish can have a broader range of colors, including orange, red, white, black, and calico patterns.
  5. Habitat: Both comet and common goldfish can be kept in similar habitats, including aquariums and outdoor ponds. However, due to their smaller size, comet goldfish may be more suitable for smaller aquariums or ponds, while common goldfish may require larger spaces due to their potential size.
CharacteristicComet GoldfishCommon Goldfish
Body ShapeStreamlined and elongatedRounded and egg-shaped
Tail ShapeDeeply forked, resembling a cometRounded, without a distinct fork
Size12-14 inches (30-35 cm)10-18 inches (25-45 cm) or more
ColorationTypically red or orangeWide range, including orange, red, white, and more
PopularitySomewhat less commonWidely recognized and popular
HabitatSuitable for smaller aquariums or pondsMay require larger spaces due to potential size
Lifespan10-15 years or longer with proper care10-20 years or longer with proper care
CompatibilityCompatible with other goldfish varietiesCompatible with other goldfish varieties
AvailabilityRelatively available in the marketWidely available in the market

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 single comet goldfish, a minimum tank size of 30 gallons is recommended. This provides enough space for the fish to swim and grow comfortably. If you plan to keep multiple comet goldfish, it’s important to provide ample space. For each additional fish, it’s generally recommended to add an additional 10-20 gallons of tank capacity. This ensures that each fish has enough room to thrive without overcrowding.

You should give preference to long tanks, not high ones. For a single comet goldfish, a minimum tank length of 30 inches (76 cm) is recommended.

Water parameters

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.


Comet goldfish likes digging tank bottom substrate looking for some additional food and thus makes the water muddy. Ultimately, the choice of substrate for your comet goldfish tank depends on your personal preference, tank setup, and the specific needs of your fish. Some goldfish keepers prefer to have a bare bottom tank for their comet goldfish. This makes it easier to clean and maintain the tank as debris and waste can be easily siphoned out. Additionally, a bare bottom tank prevents the accumulation of uneaten food and reduces the risk of any substrate ingestion.

The bottom substrate 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.

Regardless of the substrate you choose, it’s essential to ensure it is regularly cleaned and maintained. Goldfish produce a significant amount of waste, and uneaten food or debris can accumulate in the substrate, leading to water quality issues. Regular vacuuming or siphoning of the substrate during water changes will help keep the tank clean and maintain good water quality for your comet goldfish.

Tank decor

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.


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 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.

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.

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 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, comet goldfish can be kept with other goldfish varieties such as common goldfish, pearlscale goldfish, or shubunkin goldfish.

Are goldfish schooling fish?

Comet goldfish are not typically considered schooling fish. In the wild, goldfish do not naturally form large schools or exhibit the same schooling behavior as certain species of fish, such as tetras or sardines. They are more inclined towards social behavior rather than strict schooling behavior.

However, goldfish are social creatures and can coexist peacefully in groups. They often interact with each other, engage in various behaviors like swimming together, foraging, and exploring their environment. Keeping multiple goldfish together can provide them with companionship and enrichment.

Gender differences: male vs female

It is quite difficult to tell between the comet goldfish male and female, especially when they are young or not in breeding condition.

However, there are a few physical and behavioral indicators that can help distinguish between male and female comet goldfish:

  1. Body Shape: Male comet goldfish tend to have a slimmer and more streamlined body shape compared to females, especially during the breeding season. Females, on the other hand, may have a rounder and fuller body, particularly when carrying eggs.
  2. Fins: During the breeding season, male comet goldfish may develop small white tubercles (small bumps) called breeding tubercles on their gill covers, pectoral fins, and sometimes the head. These tubercles are absent or less prominent in females. Additionally, males may have longer and more pointed pectoral fins compared to females. The female fish that is reproductive and ready to spawn has fat belly full of eggs.
  3. Vent Shape: The vent, located near the anal opening, can also provide some clues. In mature males, the vent may appear more pronounced and protrude slightly outward, while in females, it tends to be more rounded and less protruding.
  4. Behavior: During breeding season, males may exhibit more chasing and courting behavior, while females may show a greater interest in finding suitable spawning sites.

It’s important to note that these characteristics may not be reliable indicators until the fish reach sexual maturity, which can take several months or even years. If you are specifically interested in breeding comet goldfish, it is best to consult with experienced breeders or a knowledgeable fish expert who can provide guidance on sexing techniques.