Comet Goldfish Stats InfographicComet Goldfish, scientifically known as Carassius auratus, is a single-tailed goldfish breed in the United States. These fish are super fun to raise, although slightly difficult as well.

But don’t worry, we’ve got you covered. In this article, you will find detailed information about care, tank, breeding, balanced diet, potential diseases, and all such important topics for a comet goldfish.

Comet Goldfish History

Hugo Mulertt, a government worker, is the one who has been credited with the selective breeding of this fish, which he did from the wild Prussian Carps. This fish was first seen in the ponds of the US Government Fish Commission in Washington, DC. Mulertt then not only became a propagator of goldfish but also wrote many books on them.

That was at the end of the 18th century. But even now, the comet goldfish is one of the most widely popular choices for fish hobbyists all over the world. The reason behind their popularity is because of their active nature as well as their beautiful, vibrant colors. They also appear in diverse colors, unlike the common goldfish, which makes them a more popular choice than the latter.

Comet Goldfish Stats

Care level Medium
Maximum size Upto 12″
Minimum tank size 75 gallons
Average lifespan 14 years
Diet Omnivore
Breeding type Spawning
pH 6.5 to 7.5
Hardness 5 to 19dKH
Temperature 60F to 75F
Temperament Peaceful
Order Cypriniformes
Family Cyprinidae
Genus Carassius
Species Carassius auratus auratus

Appearance: Comet Goldfish Body

Comet goldfish dietWhen it comes to appearance, comet goldfish are pretty similar to that of a common goldfish, except they are slightly smaller and slimmer. The main feature that distinguishes them is their long, heavily forked tail. Their slim body only has a tail fin and a single anal fin. In contrast to the common goldfish having stiff fins, the comets have these long, flowing ones. Because of this kind of tail, they have been named comet-tail goldfish.

Comet Goldfish Coloration

Like the traditional colors you see in typical goldfish, they also mostly come in yellow and orange or orange and red. However, selective breeding makes it possible to find comet goldfish in a bunch of different colors like red and white, which is more popularly known as the Sarasa Comet. There are also full white comet goldfish and yellow comet goldfish, and ones that are brown and even black. The black ones are technically Koi hybrids.

Another unique coloration of comet goldfish you might find is the nacreous kind, which is a cloud-like color; it’s basically like a uniquely foggy fish coloration. They also have nacreous patterning on their bodies. They are sometimes referred to as Shubunkin goldfish and are comparatively more expensive since they are rare.

All colors are pretty in their own way, and choosing different colored comet goldfish for a tank is the best choice if you want your tank to hold more diversity.

Comet Goldfish Care

Most people will tell you that goldfish are the easiest to take care of. This is exactly why most aquarists choose goldfish as the first fish pet when starting off. While there is nothing wrong with that notion, the same thing is not applicable for all kinds of goldfish. In fact, unlike other goldfish, comet goldfish are comparatively difficult to take care of.

Are They Easy to Raise?

It’s true that comet goldfish are quite hardy, and they have great adaptability to different types of environments, but there is still a lot of work to do if you want to raise one. They have vastly different kinds of needs from other fish because of their unique nature. You will have to expend quite a bit of time and energy on raising them.

Comet Goldfish Diet

Like most goldfish, comet goldfish are omnivores, so you have to give them a wide range of food. Dried foods are best for them as these have all the nutrients comets need. But you can also choose live foods like bloodworms, larvae, small insects, and frozen foods as alternatives. For the plant-based part of their diet, you can give them peas, lettuce, broccoli, and such.

When and How Much Should You Feed Them?

Adult comet goldfishMake sure the food is high quality instead of old and rotten if you want them to grow healthy as well as have better coloration. Feed them about two to three times a day in the right amount. The right amount here is the amount you think they will gobble up within two minutes. Make sure never to overfeed them as it can cause them to bloat, which is a very serious issue.

Moreover, giving too much food, food that they won’t be able to finish quickly or at once will also hamper the water quality. The more they eat, the more waste they will produce, and the more waste they produce, the more the ammonia level within the water will rise. And your job is to keep the water parameters as consistent as possible, so be very calculative of this.

Comet Goldfish Health And Diseases

Many kinds of health problems may befall your comet goldfish, so you have to be very watchful of them if you want them to live long and healthy. It doesn’t matter whether you keep them in a tank or a pond; they can still become victims of a wide range of health problems. Compared to other fish, they have lower immunity and resistance to diseases, so you will have to face some trouble with that.

Common Diseases They Can Get: Ich

Common diseases suffered by comet goldfish are the Protozoan diseases like Ich. Because of poor water conditions or increased stress levels (either due to inadequate food, incompatible tank mates, or a small tank), Ich is a disease faced by many fish. Ensure the best tank maintenance to prevent this from happening. Keeping the water parameters consistent is very important.

Common Diseases They Can Get: Rotting Fin

Another health problem is a rotting fin, which can be caused by bacterial infection. Since comet goldfish have delicate fins, they are very much prone to this. You will notice that their flesh is becoming frayed and even discolored. If it gets too bad, you will see bits and pieces falling off and floating in the water. As you can guess, this can be quite fatal. Luckily it isn’t difficult to treat this disease. Quarantine the affected fish and use antibiotics to get rid of the bacteria, and they’ll heal within a while.

Common Diseases They Can Get: Swim Bladder Disease

Another common goldfish disease that you should watch out for is the Swim Bladder Disease, which can be caused by bacteria, constipation, or other causes. As this can be a permanent issue, you will have to consult a veterinarian and see your treatment options. It’s not something you can manage yourself.

Comet Goldfish Lifespan

The natural comet goldfish lifespan is around five to fourteen years. As you can see, it is quite a wide range, which means the lifespan can vary largely from fish to fish. Sometimes they can live even longer than 14 years. If you give them adequate space, a healthy diet, and treat their diseases timely, then they might reach over 10 years of age.

Otherwise, they may die within only a couple of years.

Comet Goldfish Size

The maximum comet goldfish size can reach around 12 inches. But that is assuming they have enough space to grow, so they usually reach that size in a large pond. In aquariums, they might be unable to reach their full size. But if the aquarium is big enough, then they will definitely reach quite close to this length. When you buy it from a shop, it will usually be a juvenile small comet goldfish only a couple of inches long.

Comet Goldfish Tank Size

As mentioned before, comet goldfish are popular among fish keepers because of their hardy nature. Compared to most other goldfish breeds, they are very active. So you will often see them dashing back and forth in its tank at all times without staying still at a place for too long. Consequently, they also need a wider space to have fun.

Tank Size: More Comet Goldfish, Outdoor Pond?

That’s why it’s best to keep comet goldfish in outdoor ponds and pools. They are often kept with koi fish.  Generally, if you are getting more than four comet goldfish at once, it is best to keep them at a pond to give them adequate space. Though they are small, a large number of them together being all active will not work out in a small space.

Tank Size: One Comet Goldfish, 75-Gallon Tank

However, if you do not have any ponds or pools, then an aquarium will also work. For a single goldfish, a 40 to 50 gallons tank should suffice, but it’s recommended that you settle for 75 gallons instead. Remember, you cannot put them in a tiny fish bowl like other goldfish! A small tank will hamper their growth, which can cause them to suffer from severe illness late on.

Tank Size: How Many Gallons for Each New Comet Goldfish

Now, if you want to buy more than one comet goldfish, you have to add at least 50 gallons for each fish. So if the tank size for one fish is 75 gallons, the tank size for two will be 125 gallons, and so on. As you can guess, it gets quite difficult to keep more than two in a tank as you would need quite a large one, which will be expensive and hard to manage. That is exactly why it’s best to keep a group of them in a pond instead of a tank.

Water Conditions Of Tank

Since these fish are descendants of wild carp known as the Prussian Carp, you have to create the kind of water condition that also matches the wild habitat of Prussian Carps. To give you some insight, they are native to Asia and mostly reside in slow-moving water bodies like rivers. But you will also find them in lakes, ditches, and large ponds.

Water Oxygenation and Hiding Places

So when it comes to your aquarium, first of all, you want the water to be properly oxygenated and also for there to be hiding places for the goldfish to feel safe. That’s why you should decorate the tank with plants like Anacharis, Java Fern, and Hornwort, which can also act as food. Finally, make the substrate with gravel. The water parameters are very specific for these fish, so make sure to monitor them on a regular basis.

Water Temperature

Goldfish require cold water, so keep the tank in a cold room with no heat source nearby. The water temperature should be somewhere between 50F to 75F. If it is any more than that, you will be putting them at risk of incurring lifelong damage to their nerves. If you are in the US, the normal room temperature is within that range in most places, so you won’t have to worry about adjusting it all the time.


Next comes filtration. Comet goldfish, more like goldfish in general, produce a huge amount of biowastes. If the filtration is not done properly, this can obviously impact the condition of the water in the tank. So you can use a hang-on-back filter for the goldfish tank for better convenience. But if you have the necessary budget, a canister filter would be the best choice for a filtration system.

Comet Goldfish Tank Mates

Comet goldfish breedingAn aggressive temperament characterizes most active fish, but comet goldfish are definitely not like that! Though they always love to play around, they are quite peaceful and friendly and will rarely ever mess around with each other or fish of other species. They mind their own business and just have fun in their own way. It is always a delight to watch them being all happy and energetic.

What Fish to Avoid and Why

Though they get along well with everyone, you still shouldn’t choose any type of small fish as their tank mates. The reason is quite simple — they might be mistaken for food by the comets. But that aside, it is still a little difficult to find appropriate tank mates for a comet goldfish. It isn’t that the temperament will not be compatible with others. Rather, it is the water parameters.

Water Parameters, Fish Activity, and Tank Mates

Most species of fish prefer either normal water temperature or a warmer one, but comet goldfish need cool water. Another reason is feeding. They are active in nature, so they are also quite quick to grab food. They will always take as much as possible even if their hunger is met. So for fish who are slow and shy, they might miss their chance.

Comet Goldfish Breeding

When it comes to comet goldfish, you will have a hard time getting them into breeding. It is completely impossible for them to breed in a small tank, and they won’t do it no matter what you do. If you want them to breed, you will have to arrange a massive space for that with the right, natural environment. This means the best place for them to breed is in ponds.

Breeding in a Pond: What To Do

You will definitely see success in a goldfish pond with a large number of male and female goldfish. If you want to trigger the breeding process, you have to replicate the environment of their natural setting. Try to imitate the warmth of spring, which is usually their breeding season. Keep the water cool for about a month, then start slowly raising the temperature to about 70 degrees.

Once you have reached that temperature, you will start to see that the fish are pairing up and getting ready to breed. The males will chase around females throughout the pond, which can get quite chaotic. But it will be exciting to watch nonetheless. Use artificial plants or breeding mops for best results.

Comet Goldfish Eggs

They can lay up to 1,000 eggs at once, which can be quite explosive for your fish population. Since there will be a lot of eggs, you will have to remove some of them if you want to improve the survival rates. The comet goldfish will never display any kind of parental behaviors and won’t show any signs of protecting the eggs, so you can remove them easily. Not to mention how they often eat their own eggs, which isn’t exactly healthy for them.

When Will the Eggs Hatch?

The eggs will hatch in about a week. The fry will stay inside their egg sacs until the next few weeks, by which time they will be old enough to start free swimming around the place; when you start seeing that, you can start giving them food. The foods can include Infusoria and baby brine shrimp. These proteins will help them grow fast and healthy!


And that was all you needed to know about a comet goldfish if you are planning to get one for yourself. Let’s take a look at all the important points once again:

  • Comet goldfish careComet goldfish come in a wide range of colors due to their selective breeding.
  • They perform the best in a large pond alongside other goldfish and koi fish.
  • Since they are very active in nature, they need a large tank to swim around in, so you can’t put them in a small fishbowl.
  • They produce a large amount of waste, so water filtration has to be powerful.
  • Their lifespan depends largely on how well they are taken care of.
  • Comet goldfish do not breed in a small space and without the natural environment.
  • Since they lay a lot of eggs at once, you have to remove some of them to improve the survival rate.

Comet goldfish are a delight to raise, though you will have to do quite a bit of work to raise them. However, it’s all worth it in the end when you see them playfully racing around the pond!

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