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Comet Goldfish Care, Information, & Pictures (Breed Guide)

With the endless variety of Goldfish out there, it seems like the Comet Goldfish is the one few serious aquarists consider. But I personally feel that these are some of the most desirable Goldfish out there.

Comet Goldfish are significantly hardier than Orandas and other fancy breeds. They thrive in outdoor ponds, grow quite large, and will readily breed in either aquariums or ponds. Let’s get to know the Comet Goldfish!

What are Comet Goldfish?

With the intense metallic color of its flanks and long, deeply forked tail, it’s easy to see how the Comet Goldfish gets its name! But where do these Goldfish originate?

Most aquarists know that China is the original homeland of all Goldfish. These East Asian carp were bred in ponds for thousands of years to provide food for the cities and villages of the region.

However, a few gold-colored individuals were discovered one day lost to antiquity. These beautiful, seemingly lucky fish were carefully raised and bred, passing on their golden genes. From them come all of the Goldfish in today’s aquarium world.

Most Goldfish breeds are of Asian origin; the Chinese and Japanese are especially good at breeding local varieties like the Japanese Ryukin and Black Moor. However the Comet is actually quite recent as far as Goldfish lineages go!

They have their roots in the United States, of all places. Hugo Mulertt, a government worker, developed the breed in the 1880’s from the Common Goldfish line.

While not as different in form as Orandas or Moors from their wild roots, the Comet was and is still recognized as a distinct breed of Goldfish! So how do we care for these shapely, long-tailed Comets?

  • Common Name: Comet Goldfish
  • Scientific Name: Carassius auratus
  • Origin: United States
  • Length: 8-20 inches
  • Aquarium Size: 30 gallons
  • Temperament: Peaceful
  • Ease of Care: Very Easy

Caring for Comet Goldfish

This sections goes into detail on aquarium size requirements, water parameters, diet considerations, and much more.

Aquarium Size

Goldfish are pretty sizable fish and Comets are no exception. In fact, they are larger than the average fancy Goldfish, capable of growing as large as their wild ancestors (up to 20 inches).

Unfortunately, Comet Goldfish might be the breed most likely to end up in a bowl. They get mixed in with Common Goldfish as cheap feeder fish or end up at fairgrounds as carnival prizes. These Goldfish inevitably end up dying very young and far smaller than what’s possible for them.

Comet Goldfish will live for decades if well taken care of and will reach 6-8 inches by 2-3 years of age! Therefore, you should be thinking about a long-term tank. Given how large they can grow a 30 gallon aquarium is the absolute minimum for an adult Comet.

I recommend getting an even larger aquarium if they continue to grow. Or better yet, move them to an outdoor pond where they can swim free of walls and graze on the abundant algae and insects that thrive in ponds!

But as young fish they will do just fine in aquariums as small as 10 gallons. Just be ready to upgrade in a few months.

Water Quality

Goldfish are famously tolerant of a wide range of water conditions. This is because carp are accustomed to living in foul, still waters that other fish can’t tolerate. In this respect they are like aquatic pigs, which is why they are so popular to raise as food fish around the world.

That said, just because they can live in stagnant water doesn’t mean that you should give that to them. A filter for your Goldfish provides water flow, helps break down nitrogenous waste (ammonia, nitrite, nitrate) into harmless byproducts, and ensures oxygen and carbon dioxide exchange happens naturally.

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Comet Goldfish can tolerate slightly elevated ammonia levels but they may show black patches, red burns, and other signs of stress. Instead, we should strive to keep toxic chemical levels as close to 0ppm as possible.

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Comets are very versatile when it comes to water chemistry as well. They do just fine in slightly acidic to alkaline conditions (pH 6.0-7.5+) but are happiest in alkaline to neutral water (pH 7.0).

They are also tolerant of a wide range of water temperatures. Unlike fancy Goldfish, Comets don’t need a heater. In fact, temperatures above 75℉ tend to stress them out. Instead they should be kept at room temperature or cooler for best health.

Comet Goldfish are some of the best outdoor pond fish. They acclimate quickly to being kept outside in temperate climates. They will also overwinter in deep ponds. 

Even if the pond ices over, so long as a hole is kept open in the ice for gas exchange, your Comet Goldfish will hibernate until spring (and mating season) arrives.

Plants & Substrate

Comet Goldfish are easy to care for in most respects. But they can be a little rough on your plants and substrate. Goldfish simply love to dig and spend most of their time either begging for food or looking for it along the bottom.

As they dig they disturb plant roots constantly, which plants hate. And they dig little pits that mess up the look of your aquascaping. In short, they have rather poor manners so you’ll need to plan a bit for their bad habits.

If you really want to use live plants in your Goldfish aquarium try giving the plants a month to get solidly established. Or buy your Comet Goldfish while they are too small to do too much damage. That way, as the Goldfish mature the plants will have developed strong root systems that will withstand the occasional Goldfish storm.

Plants with thick root systems include Amazon Sword plants and Vallisneria. Be careful when buying soft leaved plants like Anacharis and Cabomba because Goldfish find them absolutely delicious! They will likely be uprooted and eaten.

Also take time to decide on whether you want to go with sand or gravel. Sand is beautiful but your Goldfish will sometimes leave deep pockets where they’ve decided to dig and found food. Gravel is harder for them to lift about and the holes self-fill much more often than sand.

Tank Mates for Comet Goldfish

As peaceful as all Goldfish are, Comets are fairly easy to match with other fish. The main issue to choosing good tank mates is temperature. Comets are cool to coldwater fish and won’t do well alongside Angelfish, Gouramis, Tetras, and other tropical community fish.

Instead, try Livebearers (Guppies, Mollies, Swordtails, etc), larger Barbs like Tinfoil and Eight Striped Barbs, Danios, and other cold-tolerant species. Dojo Loaches are popular to keep alongside Goldfish.

Koi might be some of the best pond mates for Comets. These larger cousins to Goldfish come in several varieties that are bred to be best appreciated from a top view. The graceful form and flowing tails of Comet Goldfish make them great additions to any Koi pond. While smaller, they are very closely related carp and have nearly identical care requirements.

The only fish you need to really watch out for are aggressive tank mates. Cichlids, large Catfish, and other territorial bottom dwellers can make things very difficult for Comets. Goldfish don’t really understand what a “territory” is and will be constantly nipped by these fish.

Good Tank Mates for Comet Goldfish

  • Barbs, Danios, Koi, and other Cyprinids
  • Livebearers (Guppies, Mollies, Platies, etc)
  • Dojo Loaches
  • Chinese High Fin Sharks
  • Other Goldfish

Poor Tank Mates for Comet Goldfish

  • Gouramis, Tetras, Angelfish, and other warm water tropical fish
  • Cichlids, large Catfish, and other territorial fish
  • Small invertebrates (shrimp, snails, etc)

Feeding Comet Goldfish

Comet Goldfish are very easy to feed because if it hits the water they are likely to try it! While you may know folks that offer their fish bread to eat, I strongly advise against feeding your fish human food.

That said, Goldfish are omnivores just like us! That means they need a healthy balance of plant and animal matter to thrive. Stick to a slightly vegetarian bend for your Comet Goldfish: boiled vegetables like spinach, squash, and peas are great treats for them. Prepared foods rich in vegetables like spirulina powder are also inexpensive and even more convenient.

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Comet Goldfish also need some animal protein, though. So be on the lookout for worms, insects, and small snails to toss in the aquarium.

If you have Ramshorn Snails the adults are often large enough not to be eaten while providing a regular source of tasty baby snails for your Goldfish to eat. Frozen or live brine shrimp, blood worms, earthworms, and tubifex are all favorite foods of theirs also!

Breeding Comet Goldfish

Goldfish breeding is quite easy to do so long as you have healthy, well-fed Comets. Pond breeding is much easier as Goldfish prefer spawning in tangled plant thickets.

Also, they respond to seasonal variations in temperature to know when to spawn. Goldfish spawn in the late spring to early summer once the ice has melted and they have had time to rebuild their fat reserves.

Indoor aquariums typically stay constant in temperature year-round, which can complicate matters. Still, you can simulate a change in seasons with a heater and some patience!

Sexing Goldfish isn’t easy either. But Comets and other breeds that are close to the wild variety are easier than fancy Goldfish in this respect. Once your Goldfish are sexually mature (5-6 inches), the females will plump up slightly. This is usually more obvious from above than side viewing.

Males also develop what are called breeding tubercles on their gill covers and heads. These bony lumps signal that he’s hormonally charged and ready to spawn!

Females may develop a few as well but never as many as an adult male. The male will also start chasing females he senses are close to being ready to spawn, helping you identify your females.

All Goldfish are egg scatterers. In nature, they spawn in thick tangles of weedy plants near the shore. Their eggs are sticky and adhere to whatever they touch. The adults then leave the eggs and fry to their own devices.

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Unless you’re keeping dense plants like Hornwort for them to spawn in, you’ll want to add a plastic spawning mop for your Goldfish. Otherwise they will eventually find and eat their own eggs and fry. You can then remove the plants the eggs were laid on to a fry rearing tank.

Once the eggs hatch, the young Comet Goldfish lie motionless for 3-7 days, absorbing nutrients from their yolk sacs. Once they start swimming freely, you know they are ready to begin feeding.

The best food by far for them is live brine shrimp nauplii but they may accept frozen nauplii, daphnia, or powdered fish flakes. From there, you simply need to keep the water clean and watch as they slowly mature into young adult Comet Goldfish!

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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