Comet Goldfish Fish Species Profile

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A 15 year old comet goldfish in a 100 gallon tank

The most popular aquarium fish worldwide is the Comet goldfish. These fish are best for beginners since they are hardy enough to tolerate many newbie mistakes. These long-body fish can vary in color from white to bright orange to dark brown. Properly kept, they can grow up to 12 inches or longer, so a large tank is required.

Species Overview

Common Name(s): Comet goldfish, Common goldfish, Sarasa comet

Scientific Name: Carassius auratus

Adult Size: 12 to 14 inches

Life Expectancy: 15 to 20 years

Characteristics Family Cyprinidae Origin  Asia  Social  Peaceful Tank Level  Top, mid-dweller  Minimum Tank Size  50 gallons Diet  Omnivore Breeding  Egg layer Care  Beginner pH  6.5 to 8.5 Hardness  5-12 dgH  Temperature  33 to 80 F (1 to 27 C)

Origins and Distribution

Comet goldfish originated from the Crucian carp many centuries ago. Similar to the history of the koi fish (Cyprinus carpio), comet goldfish were originally kept as a food source. Over many generations, people started to notice different mutations in color and would keep those fish separate. Countless generations later, we have the comet goldfish we know today. Further cross-breeding has resulted in many varieties of fancy goldfish, such as the oranda and ranchu, with distinctive structural features.

Goldfish have become an invasive species in areas where unwanted pets are "set free." Never release your pet fish into the wild. They may suffer a horrible fate or overwhelm the native populations. The goldfish ancestor, the Crucian carp, is native throughout Europe and Asia.

Colors and Markings

The "traditional" comet goldfish color is bright orange, where its ancestor is mainly brown with a lighter tan or gold belly. With mass spawning of any color goldfish, you are likely to see a wide variety of color variations passed onto the offspring.

Typical colors of goldfish vary from white, tan, gold, orange, and brown. The body may be one solid color, or your fish may have patches of various colors. Comet goldfish colors can vary widely and may change as the fish ages, and with varying water quality or diet.

Sarasa comets tend to have slightly elongated fins and more saturated colors. They look very similar to koi, often with deep red colors on a white body.


Since goldfish are peaceful community fish, the biggest differential for potential tankmates is fish size and temperature tolerances. Goldfish are freshwater fish, and can tolerate tropical temperatures, but it makes them very hungry and they will make a mess of your tank.

It is best to choose tankmates that can tolerate slightly less than tropical temperatures, around ambient room temperature, and are large enough to not be accidentally eaten during feeding time.

Good tankmates for goldfish include other goldfish, a school of zebrafish, ornamental minnows or snails.

Due to their wide temperature tolerances, goldfish are also suited to outdoor pond living. Since they do not grow as large as koi, they make a sensible addition to smaller ponds. They can be kept with koi in larger ponds if you choose.

Comet Goldfish Habitat and Care

Comet goldfish make excellent beginner pets because they can tolerate less than ideal water quality. However, this isn’t an excuse to skip your usual maintenance!

The biggest consideration with keeping comet goldfish is to provide them with enough room to grow and thrive. A small 10 or 20-gallon tank may be okay for the first few months, but starting with a 50-gallon tank or larger will ensure a successful future. A fishbowl is not an appropriate home for any fish.

Comet goldfish like to forage around in the substrate, so gravel or sand is a good substrate to use. You may see them pick up a pebble and carry it around for a bit, but it shouldn't get stuck. In the very unlikely event that something does get stuck, do not panic. Your fish can still breathe around the obstruction while you call for assistance.

This foraging behavior also means that comet goldfish are frequent tank redecorators and will often uproot plants and decorative items. They are also known for eating live plants, and not because they are hungry.

Comet Goldfish Diet and Feeding

Comet goldfish do best when fed a goldfish-appropriate pelleted diet. You should look for a protein around 30 to 32% and pellets will retain their nutrition better than flakes and not make a mess of your tank. There are many goldfish pellets available in pet stores.

Depending on their tank temperature, you may feed your comet goldfish once or twice a day. If your tank is less than 70F (21C), you may feed once a day, but 70F or above, feed twice a day. Your goldfish will always act hungry, so you can supplement their diet with low calorie, low protein treats such as shelled green peas.

Gender Differences

Comet goldfish being kept in a suitable, roomy environment with good water quality and good nutrition can develop external sex characteristics.

Sex differentiation is more common in comet goldfish kept outside and exposed to normal seasonal changes.

Male comet goldfish will develop small papules on their operculum and the leading edge of their pectoral fins. Owners often mistake these for tumors, which is not the case. They may be more or less pronounced depending on the season.

Like many other fish species, females tend to be rounded and larger than the males, regardless of any other external differences.

Male comet goldfish with breeding tubercles on pectoral fin

Male comet goldfish with breeding tubercles on pectoral fin

Jessie Sanders

Breeding the Comet Goldfish

Comet goldfish are very messy spawners, broadcasting eggs and sperm throughout their tank or pond. Breeding usually occurs in the spring for outdoor systems. If your fish are kept inside, you will need to match the changes in day and night light cycles and slowly increase the water temperature.

It is very common for comet goldfish to eat the spawned eggs, so if you want to keep their progeny, move the fertilized eggs to a separate system as soon as possible.

More Pet Fish Species

If you like the Comet goldfish, here are some other species you may find interesting:

  • Zebra danio (Zebrafish)
  • Betta fish
  • Mollie fish

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