Comet Goldfish: Species Profile, Diet, Tank Setup and More

Featured Image - Comet Goldfish
Featured Image – Comet Goldfish
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: April 12, 2024
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If you started with a traditional goldfish as your first pet and are now seeking a bit of diversity in your fish tank, consider introducing a comet goldfish. They are perfect for both indoor and outdoor settings, and are easy to care for while being excellent aquarium mates. Learn more about the upkeep, habitat specifications, and common health concerns of this cherished species in our comprehensive guide.

Article Summary

  • Comet goldfish, which are mass-bred as pets and feeder fish, are thought to be descendants of ryukin or fantail goldfish, and are easier to breed than some other goldfish varieties, but all goldfish ultimately come from the wild prussian carp.
  • A minimum of 50-gallon tank for one comet goldfish, with more gallons needed for additional fish.
  • Comet Goldfish are omnivores and should be fed a varied diet of commercially available food, live/frozen food, and some veggies.

Species Overview

Common namesComet goldfish, common goldfish, sarasa comet
Scientific nameCarassius auratus
Size12 to 14 inches
Lifespan15 to 20 years
DistributionCaptive worldwide
ColorOrange, yellow, red
Minimum tank size59 gallons
Place in the tankTop
Care levelBeginner

History and Background

Despite being one of the most well known species there is more to goldfish’s history than you know. Read on to find out about the origins of this popular fish.


All goldfish come from the same ancestor: the wild prussian carp. Originally a pond fish species kept in outdoor ponds as a food source and Asia, fish keepers started to notice that some fish were more brightly colored than others. These fish were pulled aside and kept as favorites and bred into the many goldfish varieties we have in the aquarium hobby today.

It is thought that comet goldfish are descendants of the popular ryukin or fantail goldfish.

Why are comet goldfish so cheap?

They are well known for being very cheap when purchased at pet stores. This is because they are mass bred as pets and feeder fish. These hardy little fish are well known for their reproductive abilities in the aquarium trade, and are easier to breed than other varieties of goldfish.

Are comet goldfish good pets?

Comet fish are excellent companions and will provide years of entertainment. These vibrantly colored fish are perfect additions to a goldfish tank or kept by themselves.

Are comet goldfish easy to take care of?

No! Despite being a common household pet goldfish produce some of the most fish waste out of all freshwater fish. This means lots of tank maintenance which can be challenging for beginner aquarists.

Can comet goldfish live in tap water?

No fish should be placed in tap water unless it has been properly tested for water parameters and other trace chemicals that can be harmful to fish such as lead, chlorine, and high amounts of copper. If your water source has any traces of these elements, or high nitrates then it’s best to treat it with a water conditioner or purchase spring water.


Comet Goldfish In An Aquarium
Comet Goldfish In An Aquarium

Comet goldfish are a popular alternative to the common goldfish due to their tail shape, but that’s not the only thing that makes this species special. Read on to find out about more special features of comets.

What do comet goldfish look like

Comet goldfish follow the traditional appearance with bright orange coloring, a rounded body, and a single anal fin and tail fin. Despite being a single tail goldfish the comet has a deeply forked tail which earns it it’s name as it looks like the tail of a comet streaking behind the fish.

Despite looking similar, the comet and common goldfish are two different varieties. Differences include the common goldfish being larger, having less of a forked tail, and not as many color varieties.

Another goldfish species that is often mistaken for the comet goldfish is the Sarasa comet. While similar looking, the sarasa have elongated fins and look like koi.

How to tell the gender of a comet goldfish

Females tend to be rounder and larger than the males. Males have small bumps or papules on their operculum and pectoral fin. These are often mistaken for tumors.


The operculum is a support structure made out of bones that covers fish’s gills. It both protects the gills, and allows water access to the gills by opening and closing. If a fish is on land it will close its operculum to try to preserve moisture within the gills.

Sexual differences in comet fish will be more obvious in pond comets as the differences usually appear in preparation for the breeding season. Other comet goldfish that are kept in a tank should have a replicated light cycle and water temperature of the natural environment.


Comet tail goldfish are known to come in a wide variety of colors and markings including white, orange, brown, gold, and tan. Colors may be solid or your fish may have patches of different colors.

As your fish ages you might notice their colorings or markings begin to change. This is completely normal. Changes in water quality and diet can also affect coloring, like goldfish turning white.

How big do comet goldfish get?

The maximum comet goldfish size can reach around 12-14 inches, making it necessary to have a properly sized goldfish tank.

How fast do comet goldfish grow 

In excellent conditions freshly hatched fry can grow by 50% body length every week for the first few weeks of their life. It takes these fish roughly 3 to 4 years to reach their adult size and most aquarists agree that you should expect them to grow roughly one inch per year until fully mature.

Growth rate and total comet goldfish size is dependent on conditions, space, and diet, and the higher quality the larger they will get.

Temperament and Tankmates

Two Goldfish Side by Side inside Fish Tank
Two Goldfish Side by Side inside Fish Tank

Be aware of an individual’s temperament, comet tailed goldfish have different personalities and while this list is based on experience not every fish may work with your comet. Be willing to experiment to find suitable tank companions for you and your goldfish.

What fish can live with comet goldfish 

As they are fairly peaceful, you’ll notice that they get along with almost everyone. To find suitable comet goldfish tank mates take these points into consideration

Comet goldfish are fast swimmers and enjoy chasing other fish in the tank. However, they are large and and may have a hard time hiding from attackers or fish that are larger than them.

Comet goldfish are cold water fish and prefer temperatures between 60 and 70 degrees. Tropical fish will not make good tank mates.

Goldfish will eat plants, small insects, algae and anything else they can get their mouth on, so small fish, especially ones with spikes or spines will not make good tank mates for comet goldfish.

Top 5 tank mates for comet goldfish

1. Common Carp

Distantly related to comet goldfish, common carp require similar conditions and are excellent if you are keeping fish in a pond 

2. Shubunkin Goldfish

A similar variety of goldfish, shubunkins have long flowy fins and a slender body. They are of similar speed to comet’s and won’t outcompete them.

3. White Cloud Mountain Minnows

A peaceful species that you should ensure is grown to their full size prior to adding them to your tank. They are fast and you will likely see your goldfish chase them around the tank playing. If your comet does accidentally swallow one it’s okay as they don’t have any spikes or spines.

4. Adult Mystery Snails

Snails can be excellent companions for goldfish as they will help clean up the mess left behind. However, small snails will be eaten, so be sure to only keep mature ones.

5. Koi

Another distant relation of the comet goldfish, suitable for outdoor pond fish.

When searching for other fish to keep as companions for your comet goldfish you should avoid slow moving fish such as the fancy oranda, ryukin, bubble-eye, or any fancy goldfish. While the two won’t fight your comet will outswim your fancy goldfish and thus outcompete it for food. Other goldfish that would do well with a comet include common goldfish, pearlscale, and fantail.

How many fish you can keep in your tank really depends on how large of an aquarium you are willing to keep and maintain.

Tank Requirements

Fish Tank Being Filled with Water
Fish Tank Being Filled with Water

Many first time fish owners miss the mark when it comes to tank requirements for comet goldfish. Don’t let pet stores fool you into putting your goldfish into a small bowl or tank, these fish need lots of room and require pristine conditions.

What size tank do comet goldfish need?

For one comet goldfish you need a minimum of a 50 gallon tank. Multiple comet goldfish require an extra 15 gallons per fish. The goldfish tank requirement discourages many people, but these fish are better kept in a large pond.

Remember any additional fish will need a larger gallon tank to happily coexist. Also, larger habitats will result in bigger fish since there will be less competition for food.


If you have a small tank for your comet goldfish you will have to perform more frequent water changes in order to maintain proper water parameters.

How many comet goldfish per gallon

You can keep 1 comet goldfish in 50 gallons, with a larger tank needed for other fish.

Water Parameters

Tank Size>50 gallons
Water typeFreshwater
Water Temperature60-70
Water pH7.0-8.4
Water Hardness100-300 ppm 

Tank setup:


While your comet likely doesn’t have a preference on what kind of substrate you use, you should choose one that is easy to clean and won’t cause any issues if accidentally ingested (goldfish are prone to eating everything!). Sand, or large gravel (at least triple the size of your fish’s mouth) are good choices when it comes to substrate.


Comet goldfish are well known for being extremely messy which means you absolutely must have a filtration system. Because of this, we recommend a canister filter over a power filter. Not only will it provide more filtration power, but a canister filter will also reduce evaporation in your tank, and allow you to add a lid to prevent any fish from escaping.


Because of the aforementioned messiness of goldfish we recommend having a pump or air stone to assist in the circulation of the water which will prevent any ammonia pockets from forming.


If you notice that your goldfish body turning black, immediately use an ammonia test kit and check for ammonia buildup. Ammonia burn is the most common reason goldfish turn black in tanks. Even a minor concentration of ammonia buildup can harm your fish and cause death, especially for small fish.

Water heater

As comet goldfish are cold water fish you SHOULD NOT have a water heater in your aquarium. Instead you should add an aquarium chiller to help maintain proper temperatures.


Comet goldfish are active fish and are not picky when it comes to lighting, which is especially nice if you have other fish that require specific lighting to show off their coloration. Regardless of what lighting effects you choose, lights should only be on for 8 to 12 hours of the day to help maintain your goldfish’s circadian rhythm and give them time to rest or sleep.


Many goldfish owners complain about algae in their aquariums due to the messiness of their fish. One way to reduce algal growth is to limit light in your goldfish tank build.


Having plants in your setup is an excellent idea as they can provide your fish with a place to rest or hide. But comet’s are well known to eat any live plants that are in their tank as omnivores. We recommend including fake plants instead to ensure that no fish take a nibble out of them!

Diet and Health

Fish flake food
Fish flake food

Comet’s will eat almost anything you give them, as omnivores they’re not picky. A high quality and varied diet will help them achieve good health and prevent diseases.

What do comet goldfish eat

Like other goldfish, comets will eat all the food you will give them, but that doesn’t necessarily mean that all the food is good for them. As omnivores, goldfish should be fed a varied diet of meat and veggies.

What to feed comet goldfish?

Majority of comet goldfish diet (70-80%) should be made up of commercially available food such as Omega One Goldfish pellets. The rest of their diet should be a variety of live and frozen food as well as some veggies. Brine shrimp, blood worms, and greens such as lettuce, or spinach provides an adequate amount of protein, vitamins and minerals.

In a large pond it might be beneficial to add live plants to supplement goldfish and other species diets.

When to feed comet goldfish?

As goldfish are prone to overeating you should only feed them twice a day for 2 to three minutes.

How much to feed comet goldfish?

These freshwater fish should be fed according to the 3 minute rule. Begin by dropping 3 or 4 goldfish pellets in your tank, and set a timer for 3 minutes. After your fish has eaten all of them you may drop 3 to 4 more until the timer is up. Avoid giving them too much food as it can cause constipation in goldfish.

Be sure to remove any excess food from your aquarium or else it may foul your tank water. While comet goldfish are very hardy fish, part of comet goldfish care is maintaining excellent tank parameters to keep them in good health. 

Common fish diseases of comet goldfish

Goldfish Floating On Top of Fish Bowl
Sarasa Goldfish Floating On Top of Fish Bowl

Goldfish are one of the most likely fishes to get disease either from poor tank maintenance, inconsistent feeding schedule, over feeding, and improper comet goldfish care. If you notice signs on your goldfish such as not moving too much, swimming to the surface, or not eating. It might be a disease causing it. We’ve listed the top three diseases for these fish below.

  • Ich

The dreaded white spot disease, ich is caused by a parasite and can affect many fish species. Symptoms include white spots on the fish’s fins and body, and itching or rubbing against objects in their tank. You can treat goldfish ich with a salt bath, water changes, and anti-parasitic medicine such as formalin or malachite green.

  • Tail fin rot

If your fish’s fins or tail look tattered or like they have a bite taken out of them they likely have fin rot, in severe cases this can even cause the fish’s fin to fall off. Caused by poor tank conditions this disease can only be treated using a broad-spectrum antibiotic such as Tetracycline.


Fish often develop a secondary fungal infection when they have fin rot due to their immune system already being down. Methylene blue is an excellent treatment option when it comes to fungal infections.
  • Flukes

If you observe a small creature on your fish’s gills or body, it likely has a parasite in the form of a fluke. Flukes enter the aquarium due to improper quarantining methods or contaminated live food. Treatment includes formalin, salt, or praziquantel which can be bought over the counter.

How long do comet goldfish live?

Keeping comet goldfish is a 15 to 20 year commitment. Many fish owners do not realize this when they purchase them from fish stores and dump them in water ways once they are tired of keeping the fish. This is how invasive species are spread which will cause problems for the natural environment and other species.


Breeding comets is possible, and is easy as long as you have enough room. They can lay up to 1,000 eggs at once, which will significantly increase your fish population.

Can you breed a comet goldfish?

While breeding comet goldfish is possible it is more difficult in the home aquarium and usually requires an outdoor pond which will replicate natural spawning conditions when the temperature begins to rise during the spring.

How to breed comet goldfish?

To begin to breed these fish you must first ensure that you have a male and female pairing. During spawning season male fish will develop small white bumps on their gill covers, female fish are generally rounder than males.

To encourage breeding, place your pair in a separate tank and reduce the temperature to 60 degrees, slowly increase the temperature by 3 degrees daily until spawning begins. You’ll notice their colors becoming more vibrant as well as the male chasing the female fish in a mating dance.


You might want to place a spawning mop in your breeding tank. This will help protect the fertilized eggs from being eaten immediately after spawning and increase their survival rate.

Once the female fish lays all the eggs and the male fertilizes them, remove the parents from the tank immediately. The eggs will hatch within a week and the fry will become free swimming 3 to 4 days afterwards. Free-swimming comet goldfish care includes feeding baby brine shrimp, infusoria, or crushed fish flakes and maintaining excellent water parameters.

If you need more info and tips on breeding goldfish, watch this video below.

How to Breed Goldfish 

Is the comet goldfish for you?

The comet goldfish is an excellent companion for fish keepers looking for a vibrantly colored peaceful fish with an excellent personality. While their maintenance is often more than what beginner aquarists realize, we think they’re definitely worth it.


In conclusion, the comet goldfish is an excellent companion, whether you decide to keep it alone or with many fish. We feel confident that you’ll fall in love with comets just as much as we have.

Feel free to share this comet goldfish care guide with your friends or fellow aquarists and good luck on your fishkeeping venture.

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