Comet Goldfish All You Need To Know: Size, Varieties and More…

The Comet Goldfish is a very common species of goldfish that is kept by millions of people across the world.

They are well loved for their charming personality and stunning color.

This fish comes in a variety of colors ranging from a vibrant orange to patterns of red and white. If you are looking to add a splash of color to your aquarium then the Comet Goldfish is ideal.

However, deciding to keep one of these Goldfish is a big decision because they do require a higher level of care. They are an active freshwater species that requires very precise water temperatures.

If you are up for this challenge then keep reading to learn everything you need to know about this fish, including care, diet, tank mates and much more…

Comet Goldfish

Comet Goldfish 101

Red Comet

The Comet Goldfish (Carassius auratus) is one of the most commonly kept Goldfish in aquariums and ponds. They are best known for their long tails which resemble comets from space!

You can find them in a variety of colors ranging from orange to red to bright yellow or even a patterned red and white.

Comets are a staple of freshwater aquariums and have a relatively long lifespan; they can live anywhere from 10 to 20 years.

This unique and tranquil fish is actually a descendant of the Prussian Carp and because of this they thrive in cold waters. They require a lot of space so you should only get one if you think you can provide them with the space they need. These fish can grow so large that sometimes they need a pond!

Expect to pay less than a dollar for each Comet you buy. They normally retail for $0.50 each.

Key Facts:

  • Experience Required: Beginner.
  • Nicknames: Comet, Comet-Tailed Goldfish, Pond Comet.
  • Color Forms: Bright Orange, Yellow, Red and White.
  • Size: 12 inches.
  • Tank Size: Minimum 50 gallon.
  • Tank Temperature: 50°F to 75°F.

  • Peaceful and active
  • Available in a variety of colors
  • Long lifespan
  • Known to interact with humans

  • Cannot be kept with tropical freshwater fish
  • Difficult to breed
  • Require a large tank
  • Eat a lot of food

Comet Goldfish Size and Appearance

Comet Goldfish Close Up

Comet Goldfish can grow up to 12 inches long.

You may be wondering how the Comet Goldfish got its name.

The answer is all in the tail!

They have a long forked golden tail that resembles a comet in space. Usually, their tail is around the same length as their body.

Just like a comet this type of Goldfish is known to be fast, darting in all directions.

These graceful movements can be attributed to the slimmer and more slender body of this fish. This differs greatly from the common Goldfish. Comet Goldfish also only have one tail and one anal fin which are more flexible than the stiff fins seen in most Goldfish.

In addition they have one wedge-shaped dorsal fin and two lengthy pectoral fins.

Their vibrant colors are also accompanied by shiny scales.

To tell the difference between males and females you should look at their fins and their body.

Males tend to have thicker pectoral fin rays. They are also slightly slimmer and smaller than females. During the breeding season males will also get spiky bumps (breeding tubercles) on the front of their pectoral fins and gill covers.

The females will be wider if you look at their body from above. This is more prominent during the breeding season when they begin to swell up as their eggs develop.

These majestic Goldfish come in a variety of colors ranging from the brightest yellow to patterns of red and white.

Original Comets tend to be either orange or red, but Sarasa Comets have patches of red and white. There are other forms too including full brown or white and even black. These fish are known as Koi or Comet Hybrids.

You can also find a Comet Goldfish with a nacreous pattern but these are known as Shubunkin goldfish.

Comets can fade in color as they get older or if they have been fed a poor diet.

Comet Goldfish Care Guide

Carassius Auratus

Comet Goldfish have slightly lower immunity compared to other fish so you have to care more for Goldfish.

For example they are more susceptible to common fish diseases such as Ich. This is caused by a parasitic protozoan which results in white spots appearing on their body and fins. It is caused by poor water conditions and stressful environments.

Swim bladder disease is another common illness. It may not always be caused by poor environmental conditions and can be the result of other issues such as constipation. Bacteria may also cause this disease. The main symptom is strange swimming behaviors.

Fin rot is another example of a bacterial disease that Comets are prone to. It results in the destruction of the beautiful fins that comets are known for.

Thankfully all of these diseases can be treated medically but for more serious diseases such as Swim bladder disease you should consult a veterinarian.

Regular water changes are needed to avoid any accumulation of toxic bacteria and prevent your Comets from catching nasty diseases.


Comet Goldfish are omnivores so they will eat both plants and animals.

Dried foods are the easiest option but sometimes they will enjoy fresh foods too (whether this is meat or vegetables). This creates a healthy and balanced diet for your comet and a varied diet is key for their coloration.

Live feeds have been proven to impact the growth rate and survival of Comet Goldfish larvae. This is because live feeds contain higher amounts of carbs, lipids, and proteins.

What Food Can They Eat?

  • Dried and Dehydrated: Flakes and pellets are the easiest option and are packed with all the essential nutrients that your Comet Goldfish needs.
  • Plants and Vegetables: A few options to consider are cucumbers, broccoli, lettuce, carrots, zucchini, blueberries, strawberries, and peas.
  • Meat: bloodworms, small insects, larvae, earthworms, snails, and crustaceans.

Comets are big fish so they need to be fed three times a day. However, to prevent overfeeding, make sure to only give them an amount that they can eat within a two minute period. This is also very important in order to avoid bloating.

Overfeeding can lead to a range of health problems such as excessive weight and fatty liver, as well as fin rot.

Their feeding cycle should also be very regular. This will help their digestion system and reduce the likelihood of falling sick. Remember that they do not have stomachs and use their intestines for digestion so they should not be overwhelmed with food.

Another thing to look out for is food dominance. This is a natural phenomenon that occurs when bigger fish in a tank outcompete the smaller fish for food and eat more. This usually happens in tanks where there are shy or small fish but can also happen in tanks with other goldfish too.

Make sure to observe your tank during feeding times so that all your fish are getting appropriate amounts of food.


Silver Comet Goldfish

Graceful and elegant are the two best words to describe a Comet Goldfish.

Their peaceful temperament and friendliness make them very compatible tank mates.

They tend to occupy all levels of the tank. They may be higher near the surface during feeding or may be lower down in the tank when playing with other species or exploring their space. They like to hide for fun and also swim around all over the place.

Their slim and slender bodies allow them to swim at fast speeds which is why you may see them darting around the tank.

Goldfish have the ability to recognize faces and are one of the few species that will interact with you. To stimulate their curiosity you can rearrange their tank every now and then by placing objects in different places. Comets enjoy exploring new surroundings and are incredibly adventurous.

Comet Goldfish Tank Set Up

Comet Goldfish Tank

Comet Goldfish are only bred in captivity.

However we can look to their wild cousin, the Prussian Carp, as their natural environment will be very similar to their ancestors’.

The Prussian Carp was once native to the colder, slower-flowing bodies of water found in Asia. This includes rivers and naturally occurring lakes and ditches. Although they are a freshwater species there has been some evidence that Comets have the ability to tolerate and adapt to slightly brackish waters too.

So what does this mean for your aquarium?

Comets thrive in planted colder water temperatures.

The idea water parameters are:

  • Temperature: 50-75°F
  • pH: 6.0-8.0
  • Water Hardness: 12 dGH

Temperature is a very important factor and if it is too high it can result in nerve damage. The water temperature should be checked and monitored routinely to avoid any complicated issues and additional stress.

Colder waters will naturally be less acidic as they are more oxygenated than warmer waters.

Speaking of oxygen, it is essential that you provide an efficient filter such as a canister filter to keep water levels oxygenated.

Because the lighting varies among habitats in the wild there is no set level of lighting for a Comet Goldfish. The main thing is to replicate the natural day/night cycles in the tank. This means providing light during the day for 12 hours and then following this with a period of darkness.

A great advantage about this fish is that it prefers a variety of substrate, so you can use fine soft sand or slightly larger gravel.

There is also a range of plants that you can choose from including floating plants. Some good options include Java Moss, Anubias and Java Fern.

Plants also help to refresh the system by adding more oxygen to the water and providing a food source.

Tank Parameter Requirement
Minimum Tank Size 50 Gallons
Tank Type Freshwater planted
Temperature 50-75°F
pH 6.0-8.0
Hardness 12 dGH
Flow Light
Substrate Gravel or sand

What Size Aquarium Do They Need?

Comet Goldfish can grow up to 12 inches long so they need lots of space.

You will need at least a 50 gallon aquarium, but a 75 gallon tank is better. There also needs to be an extra 10 gallons for each additional Comet added.

If you want more than 4 together then a tank is out of the question and you will need a pond.

Tank Mates

Full Grown Comet Goldfish

The Comet Goldfish has a peaceful temperament and gets along with a variety of other species.

Having tank mates helps prevent boredom and loneliness.

Comets need colder water temperatures so cannot be kept in the same aquarium as tropical freshwater species that require higher temperatures.

In addition to this Comets also tend to consume a lot of food. They can be quite greedy and will snatch any food that they can find. This can lead to the malnourishment of other fish in the tank.

Good tank mates include:

There are far too many examples of fish that should not be kept with Comets.

Tropical freshwater fish are off limits as well as smaller fish as they can easily be mistaken for a snack.

Keeping Comet Goldfish Together

Goldfish are actually one of the best tank mates for fellow Comets.

They are not known for being aggressive towards each other so you won’t have to deal with any behavioral issues.

Your Comets will thrive in groups of 4-6.

Breeding Comet Goldfish

Comet Goldfish Swimming

Breeding Comet Goldfish in home aquariums is fairly difficult.

They require lots of space to breed and this is why most breeding occurs in a large outdoor area such as a pond.

Female Comets can lay up to a thousand eggs so make sure you have done your research and planned thoroughly if you are thinking of raising these fry.

To trigger spawning the temperature of the water will need to be initially decreased to around 58°F and then slowly increased towards 70°F over a few weeks. This helps to replicate the changes in season (spring) in the wild which trigger breeding.

The amount of light may also need to be shortened to around 8 hours to begin with but should then be lengthened back to a full day (12 hours).

A diet rich in protein is also needed to help trigger spawning. Make sure to include both plant and meat-based foods which will provide them with enough energy to breed.

Once you have established a breeding pair the male will actively pursue the female. He will chase her around in order to mate with her. He will then fertilize the eggs that the females lay and they will hatch around 24-48 hours after spawning.

You can tell if a female is pregnant as she will have a swollen belly and will look rounder than normal.

Eggs should be separated from the parents once they are fertilized.

Once the eggs hatch the fry will eat from their egg sac and then become free-swimming around a day or two after hatching. At this stage they can be fed baby brine shrimp, liquid fry food and infusoria.

History and First Sighting

The history of the Comet Goldfish is certainly an interesting one.

Comets were first bred in the 1800s by Hugo Mulertt, an American breeder. He selectively bred these Goldfish from the wild Prussian carp and introduced them into US government ponds. Mulertt also wrote many books about Goldfish.

They are also thought to have originated in China, closer to where their ancestors are found in Asia.

Their reliance on colder temperatures in order to survive is attributed to their ancestors, the Prussian Carp. These fish are thought to have originated from Siberia but are commonly found in ponds and rivers in Europe as well as Asia. They do not really resemble the Comet Goldfish in terms of color (they exhibit a silver tone) and are considered to be an invasive species in North America.

Ever since the 1800s Comets have taken the aquarium hobby by storm.

Their fascinating appearance and vibrant colors are without a doubt the reason why these fish are so desired around the globe. Even to this day they are one of the most popular ornamental goldfish species kept in ponds and tanks.

Should You Keep The Comet Goldfish? (Summary)

Comet Goldfish
Other Common Names: Comet, Comet-Tailed Goldfish, Pond Comet
Scientific Name: Carassius auratus
Family Name: Cyprinidae
Distribution: Captivity only
Size: 12 inches
Color: Orange, red, yellow, patches of red and white
Care Level: Easy to intermediate
Temperament: Peaceful
Lifespan: 10-20 years
Minimum Tank Size: 50 gallons
Tank Mate Compatibility: Most cold water species including other goldfish and axolotls.

Caring for a Comet Goldfish is not as easy as it may seem.

They require big and stimulating environments and careful planning when it comes to feeding, breeding and finding suitable tank mates. They also need slightly colder temperatures so won’t work well with warmer tropical freshwater species.

If you can manage this then they will be very graceful and elegant as they glide through the water with their flowing fins.

Comets are sure to brighten up your tank and establish a sense of serenity in your home. They have hearts (and skins) of gold.

Do you keep Comet Goldfish? Let us know in the comments section below…