Comet Goldfish: Care, size, lifespan & more

The Comet goldfish is the most common goldfish variety. Unfortunately, Comets are also the most misunderstood and often poorly treated of all the goldfish types.

Read this article to learn all about Comet Goldfish and how to give them the care they need.

What is a Comet Goldfish?

Comet goldfish are also sometimes called Comet-tail goldfish or Pond Comets.

This variety of goldfish was developed in the 19th century in the United States and was the first type of single-tail goldfish.

Comets are closely related to Common goldfish and have an almost identical body shape. This can often cause people to get the two types confused.

However, the Comet has much longer finnage than the Common variety. Most noticeable is the deeply forked caudal (tail) fin, which is carried fully erect in both species. Comets are also typically smaller than Common goldfish.

The Sarasa Comet is a beautiful variant with long, flowing finnage. They often have the red-and-white “Kohaku” coloration that’s characteristic of Koi carp. You can also find Tancho Comets that are completely silver in color except for a bright scarlet cap.

Hardy and Entertaining

Comets are one of the hardiest goldfish types and are extremely easy to keep when compared with the more delicate breeds of Fancy goldfish. This makes them a great choice for beginners!

These fish will eat pretty much anything that’s on offer, and they’re entertaining, too, often taking food from your hand. Comets are powerful swimmers, leaping right out of the water sometimes, especially at feeding times. These are also sociable fish, thriving in a busy community of similar types.

Size Matters

Unfortunately, Comets are often purchased as pets for kids. These fish can grow to measure 14 inches in length, making them far too big for the average home aquarium.

All too often, that results in the unfortunate fish being kept in a small tank or bowl without enough space for swimming, poor oxygenation, and often in solitude. Not surprisingly, many Comets don’t survive for very long.

Outdoor Pool Preferred

Elongated goldfish, including Comets, are happiest when kept in a pond.

These hardy fish can tolerate surprisingly frigid water temperatures. Hiding out in the leaf litter, substrate, and plants at the bottom of the pond, they can continue to thrive even when the mercury plummets below zero. Just remember to keep a gap in the ice open so that the fish get the oxygen they need.

When kept in a large pond in a community with other single-tailed, speedy swimmers, Comets will thrive, readily spawning, too.

How long do Comet Goldfish live?

Comets typically live for around 14 years but the range we would expect is between 5 to 15 years, there are examples of pond-kept Comet Goldfish living for longer when kept in the right conditions.
Often, they are kept in outdoor ponds alongside Koi Carp.

Origins of Comet Goldfish

All goldfish that you see today can be genetically traced back through centuries to the Prussian Carp, Carassius gibelio. These fish were first described by Bloch way back in 1782. These days, Prussian carp still inhabit a wide range across Central Asia, living in ponds, ditches, lakes, rivers, and other slow-moving waters.

Many civilizations kept common carp, raising the fish for food. However, it was Chinese fish breeders that first began experimenting with cross-breeding their carp. The resulting specimens were brightly-colored, extravagantly finned creatures. They quickly caught on among the wealthy as decorative and highly valuable status symbols.

As early as the 1500s, Chinese fish breeders started trading ornamental fish with neighboring Japan. By the 1600s, goldfish, such as early Comets, were being exhibited in outdoor ponds in Europe, arriving in the U.S. by the 1800s.

Interestingly, Comet goldfish that are kept in groups and allowed to mix and spawn naturally often produce offspring that revert to the wild carp’s silvery-greenish color.

What do Comet Goldfish Look Like?

Comet goldfish have elongated, flat bodies that taper gradually from the fish’s back and belly to the base of the tail fin. The fish’s head is wide and short, and the tail fin is short, generally standing completely erect.

How Big Do Comet Goldfish Get?

The environment in which a Comet is kept has a huge influence on their adult size.

For example, in a 15-gallon aquarium, a Comet can reach around 4 inches long. In a larger tank that’s not overcrowded, Comets can grow to measure 7 or 8 inches. Compare that with a pond environment, where these fish can easily reach over 12 inches.

Generally, if you keep a goldfish in a small tank, the creature’s growth will be stunted. Physical deformities can result from this.

Comets are fast and agile swimmers that need plenty of space to be happy. For that reason, these fish are more likely to thrive when kept as pond fish rather than in an aquarium.

What Color Are Comet Goldfish?

Comets come in a range of vibrant colors, including:

  • Reddish-orange
  • Yellow
  • Orange
  • White
  • Red
  • Red/white bicolor

Comets usually have metallic scales, although you can sometimes find them with nacreous scales that give the fish a variegated, pearlescent appearance.

There is a variety of Comet called the Sarasa, which is characterized by its voluptuous fins and red-and-white coloration that resembles a Koi carp pattern or Kohaku. There’s also a completely silver Comet with a scarlet cap that’s called a Tancho.

Did you know that Comets regularly change color? It often happens as the fish age. This is thought to be influenced by the diet and amount of light the fish receives. Most often, the fish’s bright colors fade out to white.

Is the Comet Goldfish Suitable for a Beginner?

As long as they are kept in a large tank or pond, Comet goldfish make an excellent starter fish for a beginner.

That said, Comets, like all goldfish, produce a lot of waste, so you must carry out regular filter maintenance and tank cleaning duties so that the water stays healthy for your fish. Again, that’s much easier if you keep Comets in an outdoor pond rather than a tank.

Comet Goldfish Care Guide

Comets are rewarding, fun fish to own. Here’s our comprehensive guide to carefree Comet care!

Tank Size

The ideal habitat for a Comet goldfish is in a pond with other goldfish.

However, if you plan on keeping your Comet in a fish tank, a 15-gallon tank is the absolute bare minimum that you need to get started. Ideally, you should begin with a 20 to 30-gallon aquarium and be prepared to upsize as your pet grows. You need to allow a further 10 gallons for each additional fish.

How Many Fish Can I Keep?

When you buy your first Comet goldfish, they will be juveniles. Youngsters need one gallon of water per inch of fish. However, as the fish mature, they consume a lot more oxygen than juveniles, so you must allow more space.

What Shape Aquarium Should I Choose?

Comets are fast swimmers, so they need plenty of open water swimming space.

Goldfish need well-oxygenated water, so they need a tank that provides a large surface area for efficient gaseous exchange to take place.

For those reasons, a long tank is a better option than a tall, narrow one. Bowls are not suitable for any type of goldfish.

The tank should have a lid or cover slide to prevent dust and dirt from getting into the tank and reduce evaporation. Also, Comets are accomplished jumpers, so it’s best to have a lid on your tank to prevent accidents.

Does My Comet’s Aquarium Need a Filter?

Goldfish are opportunistic scavengers, grubbing about in the substrate and among plant roots on the hunt for scraps of food. They’ll even eat algae that they find growing on surfaces within the tank.

Unlike you, your Comet doesn’t have a stomach. The fish extracts the nutrients it needs from the food as it passes through the gut and out as waste. Consequently, goldfish are continually producing waste matter.

So, you definitely need a powerful filter unit in your tank.

The GPH (Gallons Per Hour) Rate

Filtration systems are generally rated in Gallons Per Hour (GPH). GPH refers to the rate at which the mechanical filter element of the system circulates the water around the tank.

The minimum GPH rate for a fish tank is four times the total volume of the aquarium. However, we recommend a filter with a higher GPH rate for goldfish because of the amount of waste they produce.

Although Comets are strong swimmers that won’t be bothered by a strong flow, they prefer a gentle current. We suggest using décor or plants to buffer the flow.

Water Parameters

Comets are coldwater fish that like a water temperature of 65o to 72o Fahrenheit. For that reason, you won’t need a heater in your fish tank.

Goldfish can suffer from temperature shock if the water becomes too warm.

If you live in a very hot climate, you may need to use an aquarium chiller to prevent the water from getting uncomfortably warm for your Comets.

The pH range should be in the range 6.0 to 8.0, with a water hardness of 5 to 19 dGH.

Tank Décor

Smooth, medium-gauge gravel makes the ideal substrate for a Comet tank, as the fish can forage through it easily and without sustaining an injury.

Include driftwood, smooth rocks, and other ornaments to suit the effect you want to create, but remember to leave plenty of swimming space for the fish.


Living plants are an excellent idea for any fish tank. Plants are aesthetically pleasing, they help to oxygenate the water, and they take up nitrates. This helps to keep the tank water safe and clean for the fish.

However, goldfish do tend to dig around the plant roots. Be sure to anchor your plants securely with plant weights or put them in clay pots. Goldfish are not averse to nibbling on tender leaves, too. We suggest choosing plant species that are tough and not appetizing to the fish.


A good quality LED lighting unit will show off your Comet’s beautiful colors. If you have living plants in your setup, you’ll need to provide lighting for eight to ten hours per day.  

Diet and Nutrition for Comet Goldfish

Goldfish are omnivores, eating a mixture of plant matter, algae, and meaty protein.

You can feed tank-kept Comets a daily staple diet of flake food and goldfish pellets. This diet can then be supplemented with frozen blood worms, daphnia, brine shrimp, and tubifex worms.

Pond fish do fine on pellet food alone, as they will supplement their diet from what’s available in their habitat.

Is it Safe to Feed My Comet Goldfish Live Food?

Goldfish do enjoy live food in their diet. If your Comets live in an outdoor pond, they will also eat worms, insect larvae, and water-bound insects.

However, if you buy live food for your tank-kept fish, always use a reputable supplier. Take the food out of the water it’s supplied in before feeding your fish. Live food can be a source of parasites and bacteria that could harm your fish.

Never take live food from nature!

If you have the time and space at home, you might want to consider running a small brine shrimp hatchery to provide live food for your tank-kept fish.

How Often Should I Feed My Comets?

Tank-kept Comets should be fed two or three times every day. Pond fish can be fed once per day with pellet food, ideally early in the mornings.

If you’re not around to feed your tank-kept fish during the daytime, you might like to buy a high-quality automatic fish feeder.

How Much Should I Feed My Comet Goldfish?

It’s important that you don’t overfeed your fish, as that can cause health problems.

Offer your Comets only what they will eat in two or three minutes.

Tank Mates for Comet Goldfish

All goldfish varieties are highly social animals that need to live in the company of their own kind or similar to thrive.

Comets typically do well with other varieties of elongated goldfish, such as Shubunkins and Common goldfish. They also get along fine with Koi.

Can I Breed Comet Goldfish?

Comets are relatively easy fish to breed.

In a pond, the fish will spawn during the spring when the water becomes warmer, and tank-kept Comets will do likewise if you replicate the conditions they prefer.

Sexual Differences

Like all goldfish, Comets are pretty difficult to sex. Telling the difference between male and female goldfish is not easy.

However, female fish are larger and plumper than males, especially when carrying eggs. When in breeding condition, male fish develop breeding tubercles on the gill covers that resemble small white prickles.

Spawning Tank

Set up a dedicated spawning tank of at least 20 gallons.

Fill the tank with spawning mats, lots of thick, bushy plants, and a few flat surfaces on which the eggs can be laid.

Encouraging Spawning

You can often encourage the fish to spawn by keeping the males and females apart for a few weeks prior to introducing them to the spawning tank.

Once your Comets are settled in the tank, reduce the temperature slowly to around 60o Fahrenheit. Over the following week or so, increase the temperature by 3o Fahrenheit daily until the fish begin spawning.

It’s essential that you keep the tank clean. Carry out 15% to 20% water changes each day, and use an aquarium vacuum to remove fish waste from the gravel.

When the Comets are ready to spawn, their colors become more vibrant. The male will chase the female around the tank, vibrating his body against hers until she releases her eggs. The male fish then fertilizes the eggs.

Caring for the Fry

Goldfish will eat their eggs and small fry, so you need to remove the adult fish from the spawning tank as soon as the eggs are laid and fertilized.

The eggs generally hatch within a week or so. The fry will feed on the yolk sac for the first few days and then become free-swimming.

Feed the fry on commercially produced fry food, moving onto baby brine shrimp or crushed goldfish flake when they are large enough.

Health and Diseases

Comets are generally very hardy fish, although they can be susceptible to a few common fish diseases.  

The best way to prevent disease is to keep your tank scrupulously clean and feed your Comets a high-quality diet.

You can treat all the following common conditions successfully with an over-the-counter medication that you’ll get from fish or pet stores.

Protozoan Parasites

Ich is the most common disease that affects all fish species. The disease is also called White Spot Disease. Ich appears as a sprinkling of white spots across the fish’s fins, gill covers, and body. Infected fish also flick and rub against objects within the tank.

Chilodonella and Costia are parasitic conditions that cause skin cloudiness.


Flukes are external parasites that enter the aquarium attached to fish, hidden among plants, or with contaminated live food.

You can usually spot flukes, fish lice (argulus), and worms with the naked eye attached to the fish’s body or gills.

Fungal Infections

Fungus appears as white, fluffy patches affecting the fish’s gills, mouth, and body.

Bacterial Infection

Bacteria of various species live in all fish tanks. However, fish are only attacked by bacteria if weakened by poor water quality, stress, or injury.

If you notice sores, reddened areas, or ulcers on your Comet’s body or fins, it probably has a bacterial infection.

A fish with frayed, ragged fins is most likely suffering from fin rot, another common condition that’s caused by bacteria.

Are Comet Goldfish Readily Available?

Comets are pretty much the most commonly available variety of goldfish. So, you can find them for sale in most pet and fish stores and online.

You should expect to pay a few dollars for a juvenile Comet.

In Summary

Comet goldfish are hardy, long-lived fish that can be kept in a large aquarium or pond. These fish are hugely popular as pets, being easy to care for and available in a wide range of beautiful colors.

Do you have Comet goldfish? Tell us about your pets in the comments box below, and don’t forget to share this article if you enjoyed it!

2 thoughts on “Comet Goldfish: Care, size, lifespan & more”

  1. At what age do comets start to breed? I just released 50 very small fish into my huge pond. It’s the size of a swimming pool with lots of lilies and hiding spots, plus continuous aeration. How long before they might start breeding?

  2. Where can i learn about specifics of fresh fruits and vegetables and other human foods to give to SPECIFICALLY-(COMET GOLDFISH ONLY). Right now i want to learn about grapefruit for them mostly


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