Comet Goldfish 101: Care, Size, Lifespan and Tank Setup

A standard Comet Goldfish swimming next to some plants

Comet Goldfish are a staple freshwater species that have been in the aquarium scene for many years. Many people are captivated by their beauty and unique mannerisms!

But owning one is not as easy as it seems.

In fact, Comet Goldfish care requires a decent amount of knowledge and preparation. Owning these fish comes with a number of obstacles you’ll need to overcome.

And that’s why we wrote this guide.

It will teach you all about the Comet Goldfish and how to care for them. You’ll learn about their lifespan (and how to influence it), their size, tank requirements, diet, and more!

Quick Facts

Scientific Name: Carassius auratus
Other Name: Comet, Comet-Tailed Goldfish, Pond Comet
Lifespan: 10-20 years
Size: 12 inches
Care: Easy
Diet: High-quality dried food, bloodworms, small insects, larvae, plant-based foods like peas, lettuce, broccoli, and more
Water Conditions: 65°F-70°F, 6.0-8.0 pH, 5-19 dKH
Tank Size: 40 or 50 gallons
Behavior: Peaceful
Breeding Difficulty: High (need a large tank)

Species Summary

The Comet Goldfish is one of the most popular types of goldfish in the world. It’s not hard to see why. With their unique personalities and delicate looks, they’re a joy to care for.

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These fish have been around since the 1880s. They were selectively bred from the common Goldfish and quickly grew in popularity. Because they are so easy to breed, these species can be found for sale at local pet stores, as prized at carnivals, and even feeder bait at angler shops.

Comet Goldfish are not found in the wild, but their care requirements and preferences are very similar to that of their wild ancestors.

Comet Goldfish Lifespan

Contrary to popular belief, their lifespans actually make them a long-term commitment. On average, Comet Goldfish can live anywhere between 10 and 20 years!

Comet Goldfish can stretch their lifespans even longer than that is certain conditions. Optimal water conditions and a large environment will reduce the chances of disease and help these fish thrive for years to come.


While they look similar to standard Goldfish, you’ll notice several distinct physical traits upon closer inspection. The most notable is the tail.

Normal Goldfish have short and stiff tails. Meanwhile, Comet Goldfish have flowy forked tails. Their tailfins move gracefully in the water, even when they’re swimming at top speed. In fact, the appearance of the tailfin is what gave these fish their name!

Comet Goldfish are single-tail Goldfish. This means that they have a singular forked tail with two tips rather than a twin-tail with four tips like some other species.

Accompanying that flowing tailfin are a sizable dorsal fin, a thin anal fin, and two lengthy pectoral fins. All of the fins are semi-transparent and can take on the same coloration as the rest of the body.

Speaking of color, there’s a lot of variety with Comet Goldfish. The most common variants you’ll see are yellow, orange, white, and vibrant red. You might also see the occasional brown specimen as well.

Author Note: “Spotted” Comet Goldfish are available as well. They’re predominantly white and have large spots of bright red throughout their body. These fish are often referred to as Sarasa Comet Goldfish.

Comet Goldfish Size

The maximum Comet Goldfish size when fully grown is 12 inches long (assuming they have proper space to grow).

When you buy a Comet Goldfish, it’s usually a small juvenile that’s only a couple inches long. But that will change in a hurry!

As with any fish, their environment plays a big role in how big they can get. Poor water conditions can stunt their growth and shorten their lifespan. However, Comet Goldfish are a bit different.

It’s believed that the fish have a Growth Inhibiting Hormone that will affect their adult size. The hormone adjusts to the size of their environment. So, a larger habitat will result in bigger fish and vice versa.

Author Note: That said, don’t make the mistake of thinking that you can keep these fish in tiny bowls! They still need plenty of space to stay healthy. We’ll get into the specifics of that in a bit.


Comet Goldfish care is a bit misunderstood. It’s often assumed that these fish are actually quite easy to care for. After all, Goldfish are often the first species that aquarists own as kids.

But that’s not the case here.

While Comet Goldfish are relatively hardy and can adapt well to most tanks, they do require more work than most people think. These are unique fish that have vastly different needs than most of the tropical fish you see in the aquarium trade.

To ensure that your fish has everything they need to stay healthy, you must stick to the following care guidelines.

Tank Size

At the very least, the minimum tank size for Comet Goldfish should be 40 or 50 gallons. But if you can, go with something a bit larger.

We recommend aiming for a 75-gallon tank if possible. That’s for a single fish.

The biggest mistake that you can make as a Comet Goldfish owner is to stick them in a tiny bowl and call it a day. While it’s a huge point of contention among fish owners, the effects of the Growth Inhibiting Hormone have been documented. There are still reports of fish becoming ill due to inadequate tank sizes!

If you plan on keeping a group, you’ll need to add about 50 gallons of space for each additional fish.

As we mentioned earlier, Comet Goldfish can reach lengths of 12 inches. They need room to roam!

These fish are very active and will spend their days swimming around the habitat. If it’s not big enough for them to do this, you will encounter a bevy of problems.

Truth is, the best environment for a Comet Goldfish is probably a large pond. This species is a staple in outdoor ponds. They’re often kept in large groups with Koi and other species.

Ponds offer tons of room for the fish to stay active. They’ll be able to reach their full natural length without any issues.

Water Parameters

Another big problem that aquarists face is water quality. While Comet Goldfish are not found in the wild, they are descendants of Prussian Carps. Their needs are similar to wild carps, which are found in cool, slow-moving rivers throughout Asia.

Mimicking those environments is key. Your tank or pond will need to have relatively cool water that’s highly oxygenated. Here are some parameters you need to stay on top of to keep your fish in good shape.

  • Water temperature: 65°F to 70°F
  • pH levels: 6.0 to 8.0 (6.5 to 7.5 preferred)
  • Water hardness: 5 to 19 dKH

Author Note: Because these fish have rather specific water parameter needs, you should be performing water tests and checking the temperature quite regularly. Make it a habit!  

What To Include Inside Their Tank

The interesting thing about Comet Goldfish is that they are very receptive to a well-designed environment.

It’s said that these fish can remember their owners and quickly familiarize themselves with their surroundings. Many aquarists even like to rearrange the tank or pond every once in a while to keep their fish interested.

Either way, there are a lot of possibilities when it comes to decorating your tank. Comet Goldfish aren’t super picky, but they will need some of the basics.

Starting at the bottom of the tank, use a gravel substrate to create a nice foundation for the environment. You can then incorporate fake or natural hiding spots. Everything from large plastic decorations to carefully sculpted rock caves will do.

Plenty of live plants are a must. Live plants act as a source of food for the fish (they’ll often snack on leaves). Not only that, but the plants help to oxygenate the water.

Feel free to experiment with a mix of rooted and floating plants!

You can take other steps to ensure that oxygenation levels are good. Air bladders for tanks and fountains or waterfalls for ponds are all effective. Just make sure that the pumps you use aren’t creating a water flow that’s too powerful.

Good filtration is important as well. These fish produce a lot of waste, so you’re going to need to invest in a filter that’s powerful enough to keep ammonia levels low. For tanks, a suitable hang-on back or canister filter will do (we recommend the Fluval FX4).

For ponds, you’ll have to make sure that you have some heavy-duty equipment that complements the capacity of the habitat.

Potential For Disease

Comet Goldfish are not immune to health problems. Whether you keep them in a tank or a pond, these fish can succumb to a range of health problems (sometimes they will even turn white or black as a result)

Some of the most common are Protozoan diseases like Ich. These diseases are typically caused by poor water conditions or high stress levels. It’s your job to stay on top of tank maintenance to prevent this from happening.

A full size Comet Goldfish in an open tank

Fin rot is another disease that affects Comet Goldfish. It’s a bacterial infection that affects those delicate fins. The flesh will become frayed and discolored.

If it gets bad enough, you might even see bits and pieces falling off! Luckily, this is an easy disease to treat. You can use antibiotics on quarantined fish to get rid of the bacteria.

Swim Bladder Disease affects many different fish species. However, it’s fairly common in goldfish. It can be caused by many different things, including bacteria, constipation, and more.

You’ll know your fish has it if they start to exhibit strange swimming patterns. This can be a permanent issue, so you might want to consult with a veterinary professional to see what your treatment options are.

If your Comet Goldfish gets a disease, it’s important to separate them from the rest of your fish as quickly as possible. Diseases spread quickly in closed ecosystems like a tank or pond. Just monitor water conditions regularly and you should be able to avoid major problems.

Food & Diet

Comet Goldfish are omnivores that need a varied diet. High-quality dried food is your easiest option.

Most foods are packed with all the nutrients they need, which will help to keep them healthy and improve their coloration.

You can always supplement dried food with live or frozen alternatives. Comet Goldfish like bloodworms, small insects, and larvae. They also do well with plant-based foods like peas, lettuce, broccoli, and more.

We recommend feeding your Comet Goldfish 2 or 3 times a day. Only feed them as much food as they can eat within 2 minutes. Read our guide on how often to feed goldfish if you want to learn the nitty-gritty details.

Bloat is a very real issue, so you want to avoid over-feeding. This will also help keep water quality more consistent since there won’t be as much waste floating around causing ammonia levels to rise.

Behavior & Temperament

Comet Goldfish are a ton of fun to watch in your tank. They’re very peaceful but love to stay active.

You will often find them quickly darting across your tank, which is why you need plenty of space.

Fortunately, these Goldfish are very peaceful and shouldn’t show signs of aggression toward other fish. In fact, they get along with most creatures!

The only thing you should be wary of is their behavior around small fish. Generally, small tank mates should be avoided because they can easily be mistaken for food!

Tank Mates

It can be tough to find tank mates for Comet Goldfish. It’s not because of temperament issues, but rather environment issues. These fish require cooler temperatures that could be challenging for other species.

You may also encounter feeding problems. Comet Goldfish are voracious eaters and will grab as much food as possible, which could be problematic for shy fish!

Here are some good tank mates to consider:

Author Note: As always, pay close attention to whatever fish you keep together (especially for the first few days).


Comet Goldfish breeding requires a massive environment to be viable. They will not breed in a small tank no matter what.

However, you can see success in ponds with large groups of males and females.

These fish can lay up to 1,000 eggs at one time, which will quickly raise your fish population!

To trigger the breeding process, you have to replicate the warmth of spring. Start by keeping the water cool for about a month. Then, slowly raise the temperatures to about 70 degrees.

Once you’ve reached the target temperature, you’ll see fish pairing off and breeding. Males will chase females around the environment. It can be very chaotic in a large pond!

We recommend using artificial plants or breeding mops. You will need to remove the eggs to improve survival rates. Comet Goldfish don’t show any parental behaviors and will often eat any eggs they can.

In a separate tank, the eggs will hatch in about a week. The fry will survive on their egg sacs until they are free-swimming. At this point, you can provide foods like infusoria and baby brine shrimp.

Now You’re Ready

As you can see, Comet Goldfish care isn’t as easy as it seems. These are large fish that need very specific water conditions in order to thrive.

But if you’re up to the challenge, the reward is definitely worth it. These fish are a joy to own and are capable of building a very strong bond with their owners.

We hope you found this guide helpful, no matter what you decide to do. If you’re still on the fence about getting one of these fish for yourself, feel free to get in touch with us on Facebook or in our contact us page with any questions!

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