Hepper is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Comet Goldfish: Size, Lifespan, Tank Size & Care (Ultimate Guide)

Lindsey Stanton Profile Picture

By Lindsey Stanton

a comet goldfish

It’s a bird… It’s a plane… It’s a… Comet goldfish?!

Okay, maybe it doesn’t fly through the sky, but the Comet is definitely a standout member of the goldfish family. And today you’re gonna get the low-down on the most popular variety of goldfish in the country.

Let’s dive right in!aquarium plant divider

Quick Facts about Comet Goldfish

Species Name: Carassius auratus auratus
Temperature: 40°–65° F
Temperament: Active, Community Fish
Lifespan: 10–20 years
Size: 12 inches on average, usually larger
Hardiness: Very Hardy
Tank Size: 40 gallons
Diet: Omnivore

The Little-Known Background of the Comet Goldfish

How did we get the Comet? The first Comet was actually first made by crossing a Veiltail with a Common goldfish! This gave them their longer tail but slim body. Fun fact—the Comet is patriotic! They’re the only goldfish breed the United States has contributed.

comet goldfishes
Image Credit: Hans, Pixabay

Comet Goldfish Overview

Comets fall into the “Slim-bodied” category of goldfish types. This means they have only a tail fin and one anal fin. They look a lot like the Common goldfish, but they have a longer tail with pointed tips (this is called a “ribbon tail”).


Metallic red or red and white (a.k.a. “Sarasa”) are the most commonly found. But they can also be chocolate, yellow or white! The brown ones typically change color with age. You may have heard about the newer Black Comets on the market.  These are actually a hybrid cross between a koi and a Comet, not a true goldfish. And get this: They can’t reproduce!

And if you look closely… they have tiny “barbels” or whiskers like a koi. This is interesting: If a Comet has nacreous color, it isn’t a Comet anymore – it’s a Shubunkin goldfish.

Image Credit: Kaori, Pixabay

The Sad Plight of the Average Comet

You’ve seen them packed into tanks almost as close as sardines in a tin. Usually, they’re mixed in with their Common goldfish brothers. But here’s the bad news:

Sadly, both of them are usually doomed to the life of a “feeder fish – mass-produced and sold for a dime as food for bigger creatures. (They breed like crazy!) The lucky ones are given away as prizes at a fair (which some want to make illegal).

Because they aren’t taken good care of most of their life and are kept in poor conditions, problems like disease and shortened lifespans often result. Assuming they survive, of course. This can spell t-r-o-u-b-l-e for the unsuspecting new fish keeper.

With all these odds stacked against them, do Comets actually make good pets? Depends. If you happen to get a “toughy,” you’d be surprised to learn how long they can live (which is 40+ years, in fact!) and how big they can grow – given the right care.


That 2-inch long young Comet goldfish you got at the pet store or the fair has the potential to reach over 12 inches in length as an adult. (Or even bigger in many cases.)

orange white comet
Image Credit: imsogabriel, Pixabay

aquarium plant divider

How to Take Care of Your Comet Properly

One nice thing about Comets… They’re really hardy fish. Like other slim-bodied fish, they are most similar to their sturdy carp ancestors.

Want to learn more about slim-bodied goldfish and how they differ from their fancy cousins? Check out our best-selling book on Amazon, The Truth About Goldfish, which covers in detail all varieties of goldfish, their history, and how to identify each one, with care guides and more!

When other more delicate breeds of goldfish wouldn’t survive the conditions new owners put their fish through, many times the Comet makes it out alive. Of course, they’re not bomb-proof. And they have a much greater chance of living if you take proper care of them. So, how do you do that?

Tank Size

Comet goldfish are VERY hardy goldfish. In fact… Some of the oldest goldfish in the world were comets! They have learned to adapt to a variety of conditions over thousands of years of being bred in captivity. They also have the ability to stay quite small. Read more about tank size requirements here.

Water Temperature

Unlike fancy goldfish, Comet goldfish are a bit hardier when it comes to how hot or cold their water is. They can endure freezing cold ponds all winter long! So if you don’t have a heater for them, no sweat.  But the optimal temperature is in the 65-70 degree range when they grow the most and have the best health.

You can also read more about water temperature here.

Image Credit: kaori, Pixabay

aquarium plant divider

Are Comet Goldfish Good Tank Mates?

As an athletic fish, you really shouldn’t be mixing them with fancier strains—for the sake of the fancies. Among the many reasons… Comets will hog all the food! This will leave your other fish hungry or bullied. Don’t think you can mix tropical fish in your tank, as hardy as the Comet may be.

They can still run into problems with them. The bottom line? Stick to this plan – keep Comets with other slim-bodied varieties like the Common, Wakin, Watonai, Shubunkin, and Jikin. You can thank me later

goldfishes in a pond
Image By: Monsterkoi, Pixabay

What to Feed Your Comet Goldfish

Comet goldfish eat both plant and animal material (for all you science geeks… they are omnivores). Having a good, nutritious diet is important to their growth and coloration. If you keep your fish in a pond, chances are they have access to most of the food they need already.  But if the pond is stocked full, you will probably need to add in other foods to avoid malnutrition.

For further information on feeding, check out this post.

Breeding Comets

When some goldfish owners couldn’t (or didn’t want to) care for their big Comets anymore, they did something really bad… They released their fish into a lake in Boulder, Colorado. BIG MISTAKE! Because goldfish proliferate like crazy. We’re talking up to 1,000 eggs at a time in just one spawn!  They ended up taking over everything and beating out the native species.

If you’re talking about trying to breed them at home,  that can be done indoors.  But because of how large the babies get, it’s really best accomplished in a pond. Your own pond. A period of cold temperatures followed by spring-like conditions can really help things along.

aquarium plant divider

Final Thoughts

Betcha learned something interesting you didn’t know before! Comets are really fascinating fish. Here’s the kicker: We’ve only scratched the surface on the care and keeping of this beautiful pet.

But good news—you have the opportunity to become an expert owner and watch your Comet blossom under your outstanding care.

It’s all in a new book, The Truth About Goldfish. Check it out!

Featured Image Credit: Hans, Pixabay

Related Articles

Further Reading

Vet Articles

Latest Vet Answers

The latest veterinarians' answers to questions from our database