The Comet Goldfish Breed Facts & Tips

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!

I want to learn about…

The Little-Known Background of the Comet Goldfish

How did we get the Comet?

It all started in 1880…

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.

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Breed Description Overview

Comets fall into the “Slim-bodied” category of goldfish types.

This means they have only 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”).


As far as color goes…

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.


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 stunting, 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?


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.


This is crazy:

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.)

Quick Facts

  • Temperature: 65-40 degrees F
  • Species name: Carassius auratus auratus
  • Hardiness: Very hardy
  • Lifespan: 10-20 years on average
  • Size: 12 inches on average, usually larger
  • Tank Size: 40 gallons
  • Temperament: Active, Community Fish
  • Diet: Omnivore

Breeding Comets

When some goldfish owners couldn’t (or didn’t want to) care for their big Comets anymore, they did something reeeeeally bad…

They released their fish into a lake in Boulder, Colorado.


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.

How to Take Care of a Comet

One nice thing about Comets…

They’re really hardy fish.

Like other slim-bodied fish, they are most similar to their sturdy carp ancestors.


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?

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Tank Size

Let’s get something straight here:

If you have your Comet goldfish in a bowl for its home, you need to get it out RIGHT NOW.


No goldfish – not even this kind – has much of a chance to live in there for long.  That kind of environment is a death trap with not nearly enough oxygen and full of toxins.

And I could give you a dozen reasons more, but that’s for another post. 🙂

Oh, remember how big they get?

A fish over a foot long needs space to live comfortably.

This may shock you:

But we’re talking a lot more space than you probably thought when you got yours.

40 gallons a piece is the minimum for one fish!

comet-goldfish-tank copy

Each additional fish will need at least 20 gallons after that.

You may say:

“My fish is so small now.  There’s no way it needs that huge of a tank.”

Just wait – they grow SO fast!

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 read more about temperature here.



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.

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 😉

Wrapping it All Up

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 my new book, The Truth About Goldfish.

You can check it out below:

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  1. Jasemine January 5, 2018 at 12:47 am - Reply

    Don’t you just love it when you buy two comets and then read this and realize the breeder completely lied to you?

    Currently I have two comets who live in a 10 gallon tank. One is an inch long, and the other is about 2 centimeters (I have no clue why it is so small). How old are they when they start to grow to the point were a, I will go for a 100 gallon, tank is needed? For short, how long can they live in the tank they are currently in? I am not finically ready to buy such a large tank yet, but I do not wish to put them down and I have no one to rehome them to. They currently have a filter, heater, thermometer, plenty of plants, shells, and rocks, and I do a water change every 3 months, cleaning the tank every month. so, if possible, please tell me exactly how long I have to build up the money for a larger tank? Also, thank you comet goldfish claiming to be an expert telling me every 3 gallons can hold a comet goldfish.

    Rating: 4.5
    • Pure Goldfish
      Pure Goldfish January 6, 2018 at 4:23 pm - Reply

      In a 10 gallon with two comets, do water changes every other day. This can prolong things, but I would get the new tank asap. It will be hard to maintain ammonia levels in that tank size.

  2. Marty June 16, 2018 at 10:57 am - Reply

    It is all about the biological surface are available in the water. One Colony of bacteria converts the Ammonia to Nitrite. Then another colony of bacteria sets up shop and converts the Nitrite to Nitrate. Set the tank up so that the air bubbles pull water through the gravel and keep it oxygenated for the good bacteria to form. Keep the PH around. 7.5 to 8 to maximize the efficiency/and activity of the bacteria. Set it up right and your fishes immune system will get much stronger as well.

    When your Nitrates start to get above say 20ppm (Nitrates are plant available) you can slowly step the PH down in the tank to around 6.5 to 7.0 and put in lots and lots of aquatic vegetation. Plants will best take up nutrients at that range. The plants will clean the water and add oxygen. The fish will feed them. Get tough plants or… they will also feed the goldfish.

    Just get some rocks and some of the starter solution from the store to kick things off faster.

    Keep an eye on the water. Keep the feeding to an absolute minimum for the first few weeks and then start stepping it up. Fish can easily go weeks without eating.

    Feed rate should be around 13grams per day for every square meter of plants (minimal in aquaponics gravel systems)

    Rating: 5
    • Pure Goldfish
      Pure Goldfish June 18, 2018 at 5:29 pm - Reply

      Great tips, Marty! Thanks for sharing.

  3. Cody September 13, 2018 at 9:54 pm - Reply

    Thanks for the excellent info. I had read on some sites that Comets wouldn’t survive the winter. After growing attached to my little pond buddies all summer, I was prepared to attempt to bring them inside but if they do stand a fighting chance, I probably shouldn’t put them through the stress of the move, right? I live in Missouri. Temps usually hang between 20’s – 40’s with a couple spells of very cold temps (below 0 at night). My pond is approximately 300 gallons but I plan on expanding it to closer to 600-800 gallons this fall. I have 6 Comets (Ghost, Bertha, Spot, Patches, Lt. Dan, and Sid Fishious) all between 2-3 inches. The pond also has 6 trapdoor snails and several minnows. Any recommendations would be greatly appreciated. Thanks.

    Rating: 5
    • Pure Goldfish
      Pure Goldfish September 17, 2018 at 3:33 pm - Reply

      Yep, they can survive the cold as they are tough. Just be sure it doesn’t freeze completely and there is a little hole in the ice.

  4. Brandon October 28, 2018 at 5:33 am - Reply

    Hey there, I recently bought your book – haven’t read through it all yet, but I did look through the illnesses/signs of disease bits to try and diagnose what’s been going on with my goldfish.

    I’m ashamed to say that I not only did not cycle my tank (despite knowing beforehand), but purchased several comets already. At first, I got two, which measured around 1-1.5 inches in size. One of those had a beautiful mix of orange and white – this was what caused the impulse buy. I had to get him a friend, so that made 2 total. There were very small feeders. I placed them in a 10 gallon tank, brand new, layered with pool filter sand and filtered with a HOB filter by Aqueon and a small sponge filter. I figured together, they’d circulate the water enough, provide a good place for biological bacteria to build, and help capture a little of the debris.

    I knew the 10 gallon I had wasn’t big enough, but figured regular maintenance (daily water changes) would keep ammonia levels down. In between water changes, I’d go in with a turkey baster (new, dedicated to fish tank cleaning) and pick up any large pieces of waste and leftover food to keep it all clean. In fact, this all went according to plan, as ammonia never got higher than 0.25ppm, though at the same time, nitrites and nitrates never developed either, which meant my biological filter wasn’t establishing. I had a separate plastic container where I was running a fishless cycle so that I’d have water and media ready for when I would move them to a 40-gallon I planned on purchasing (not big enough, I know, but better than a 10).

    Then, a couple days later, one of the little feeders died. The smallest one. It was very sudden. I found him still breathing, but stuck on the side of my HOB filter. Normally he’d be fine swimming by it, but now he was so weak he couldn’t get away from it. I popped him off, he swam around for a bit, and later, he died. I figured I may have given him swim bladder, as I made the mistake of feeding these first two fish flakes. Or maybe he was just young and being in the store tank took its toll on him.

    About a week later, a purchased two more feeder comets – this time a bit larger. I decided to place them in my cycling container – ensuring ammonia hadn’t built up too much (it was zero at the time) and left them there for a week. I did the same maintenance on them, albeit fewer water changes, and moved them into the tank with the little pretty feeder comet. I knew I was supposed to quarantine them longer, but I decided to put them in anyway to give the small comet (who seemed to be “depressed” – moving around less, and not as energetic as when his buddy was still there) some company.

    Admittedly there were days that got busy, where I couldn’t do water changes – but this is where I used AmGuard to “delay” the damage until I could do so. All was well for a week or two. There was a small stretch where all the fish seemed a bit lethargic, and had loss of appetite. I bought Melafix and used it, seeing the benefits it offered, and to my surprise, they seemed better than they’d been just a few hours later. But a few days later, I saw white spots, primarily on their fins.

    Ick – that’s what I got for not quarantining long enough. Surprisingly, though, by maintaining my cleaning schedule, I not only kept the ammonia levels down, I also got rid of the ick by adding ick treatment. It completely disappeared within a week and a half. I continued medicating for a week after as well, to be safe.

    However, during this transition, one of my later fish (the biggest one) started hanging out more at the bottom of the tank and not eating. After a few days of this, and trying both aquarium salt and cut peas, I decided to move him out and into another container (shoebox sized). This had an airstone and air pump running on it. He seemed to be recovering, though still not eating. A couple days later, I was doing a water change and decided to add some aquarium salt. I used warm water and salt to get it to dissolve quickly, then carelessly added it to his container without cooling it like I’d planned. He died within probably minutes due to the sudden temperature change, but I didn’t notice since I was changing out the water of the main tank.

    So at this point, two fish had died on me. One, I suspect could’ve been my fault due to the diet I provided (or just poor health), and the other was definitely my fault. However, I am uncertain as to why either of them got sick in the first place. At this point I had two fish left – the original, pretty comet that I adored, and the other larger comet I’d gotten with the big one that passed.

    Well, yesterday, the little one seemed to have gotten sick. At this point, I’ve had him for at least a month He wasn’t eating and wasn’t interested in eating. I didn’t know why. I tried the usual pellets, new seaweed pellets that were smaller in size, and the clamped spinach leaves I’d been feeding them. Tonight I decided to move him in his own container, as the other fish was doing well. The little one’s condition had deteriorated – he was moving much, much less and his breathing was very slow. He hardly reacted to stimulus at all. I filled the container with fresh, dechlorinated water, added a touch of Melafix, and added some dissolved aquarium salt (cooled). He was perky for a short time, then died a few minutes later. This time, I don’t know what did him in.

    What frustrates me is that I feel I’ve been taking almost all the necessary precautions in caring for my fish. Ammonia levels NEVER got above 0.25ppm and never stayed that way for long because I performed daily water changes. I never got the biological filter going so I had no nitrites and, of course, no nitrates. I have a variety of medications and I think I used them as intended, since I had one instance where 3 fish recovered from previously poor conditions, and another where all 3 were able to rid themselves of ick.

    This was all very long and if you’ve read all this, I thank you. I’m sorry for writing so much. I’m just angry at myself and my situation, frustrated that my unpreparedness has caused the deaths of all my fish. My question at this point is, what do you suspect could have been wrong with my fish, or how I handled them? Out of 4 fish, I’ve now had 3 die on me. Everyone tells me, “they’re just fish,” but as far as I’m concerned, they’re pets like any other, and it’s ultimately my fault that they all died. Just as you say on one of your articles, it’s beyond frustrating and saddening to have this happen. For me, what’s worse is not knowing why. Aside from maybe the first fish (and this was assumed on my part), none exhibited swim bladder. None exhibited any signs of any of the common parasites. None even got ammonia damage (split fins, fin rot, bloody veins, etc.). And like I said, my filter never established so it had nothing to do with nitrites. I’m at an utter loss as to what had weakened my fish and ultimately killed them. In every single instance, other fish in the tank exhibited no signs of malaise. I just don’t know what to do. I hope I can care for the remaining fish going forward, but I just don’t know. I know that after 2 near-deaths that I couldn’t prevent, even when I caught them in time, I probably don’t have much hope if something develops with the last one.

    Rating: 4.5
    • Pure Goldfish
      Pure Goldfish October 29, 2018 at 5:13 pm - Reply

      Please check your inbox 🙂

  5. Maggie December 3, 2018 at 6:33 pm - Reply

    So my girlfriend won a common goldfish at a fair and we now have two comet goldfish living with it. We’d love to get them properly situated in a tank of the proper size but we are living in a dorm and they won’t allow us to have a bigger tank. We’re only allowed to have the 1/2-1 gallon tank/bowls. Any suggestions on how to keep our babies alive until we are able to finish school and get a bigger home for them? These are basically our children right now and it would kill us both to find any of them sick or dead.

    Rating: 5
    • Pure Goldfish
      Pure Goldfish December 5, 2018 at 4:27 pm - Reply

      If it was me I’d put each fish in its own 1 gallon bowl (if that’s the biggest you can get), get everybody their own filter then do daily 100% water changes until they’re cycled. Feed very very sparingly.

      • Maggie December 7, 2018 at 1:13 pm - Reply

        The school just approved us for a 10 gallon tank. It will still take time to get it and switch them over but it will get done. How long should we let the filter in the new tank run before putting our fish in the tank? And one more thing that we are just noticing, one of our comets is white and red but within the past couple of days we’ve noticed that it has been getting a black spot on its tail. The same thing is happening to our common goldfish’s fins. It doesn’t seem like fin rot but what could it be?

        Rating: 5
        • Pure Goldfish
          Pure Goldfish December 7, 2018 at 5:40 pm - Reply

          Black is almost always from ammonia burning. Running the filter without a source of ammonia serves no purpose to cycle it, so you may as well add the fish with the filter then do daily 50% water changes and feed sparingly.

          • Maggie December 7, 2018 at 6:38 pm - Reply

            Thank you so much for the help. Is there a way to reverse ammonia burning or are the black spots permanent?

            Rating: 5
            • Pure Goldfish
              Pure Goldfish December 7, 2018 at 7:44 pm - Reply

              You need to get the ammonia down and keep it down.

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