One of the most commonly kept and misunderstood fish in the hobby. Single-tailed goldfish (Comets, Commons, Shubunkins) are fast-growing, highly active coldwater fish that produce enormous amounts of waste. They are best suited for ponds or massive aquariums. They will uproot plants, sift substrate constantly, and eat anything that fits in their mouths.
At a Glance
Tank Requirements
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Water Parameters
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Temperament & Compatibility
Available Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard (Single-Tail Adult)
The adult form of the standard single-tailed goldfish. Extremely active, robust, and best suited for outdoor ponds or very large indoor tanks (4 feet minimum).
Differs in 1 trait from base species
Also known as: Comet, Common, Shubunkin, Pond Goldfish
Juvenile (Grow-out)
Small juveniles commonly sold in pet stores. While they can temporarily be housed in smaller aquariums, they grow extremely fast and will quickly require their adult tank size or a pond.
Differs in 4 traits from base species
Also known as: Feeder Fish, Baby Goldfish, Small Comet
Fancy Goldfish (Adult)
Radical morphs with compressed, shortened spines and double-tails. Because of their modified anatomy, they are slow, clumsy swimmers prone to swim bladder issues. They require strictly low flow and slightly warmer water than single-tails.
Differs in 7 traits from base species
Also known as: Oranda, Ranchu, Ryukin, Fantail, Black Moor, Pearlscale
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🟢Ideal Tank MatesGoldfish (Comet / Common) Care Guide Summary
The Goldfish (Comet / Common), scientifically known as Carassius auratus, belongs to the Goldfish & Koi family group. Adults reach a maximum size of approximately 30 cm and have a fusiform body shape with a fast growth rate. Classified as peaceful, this species primarily occupies the surface, mid-level, and bottom zones of the aquarium and produces a extreme level of biological waste.
To thrive, the Goldfish (Comet / Common) requires a freshwater only aquarium with a minimum volume of 200 litres and a tank length of at least 120 cm. Water temperature should be maintained between 10°C and 24°C, with a pH range of 6.5–8 and a general hardness of 5–20 dGH. A moderate water flow is preferred. An aquarium test kit can help you monitor these values.
The Goldfish (Comet / Common) is a rewarding species to keep, provided its core environmental needs are met. This species is available in 3 varieties: Standard (Single-Tail Adult), Juvenile (Grow-out), and Fancy Goldfish (Adult). Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Goldfish (Comet / Common) Habitat Setup
When setting up an aquarium for the Goldfish (Comet / Common), a moderate water flow best suits their natural preferences. Because this species occupies the surface, mid-level, and bottom zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline, open swimming space in the centre of the tank for free movement, and sufficient floor space with hiding spots among rocks, wood, or dense planting. Useful additions include a sand substrate to accommodate their sifting behaviour and smooth gravel or rounded substrate to protect their sensitive barbels. Keepers should note that expect substrate disturbance, so lightweight décor should be secured and live planted layouts may be difficult to maintain, as this species tends to uproot or consume vegetation. Browse aquarium sand substrate options to find the best fit.
Goldfish (Comet / Common) Compatibility Notes
Classified as peaceful, the Goldfish (Comet / Common) is adaptable and can be kept singly or in a small group, offering flexibility when planning a community tank. When choosing tankmates, shy or slow-feeding tankmates may be outcompeted at feeding time and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the surface, mid-level, and bottom zones can help reduce competition and territorial overlap.
Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Goldfish (Comet / Common).
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
Frequently Asked Questions About Goldfish (Comet / Common)
How big does Goldfish (Comet / Common) get?
Goldfish (Comet / Common) (Carassius auratus) typically reaches a maximum adult size of approximately 30 cm. They have a fusiform body shape and a fast growth rate.
What tank size does Goldfish (Comet / Common) need?
A minimum aquarium volume of 200 litres and a tank length of at least 120 cm are recommended for Goldfish (Comet / Common). This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Goldfish (Comet / Common) need?
Goldfish (Comet / Common) thrives in freshwater only conditions with a temperature range of 10–24°C, a pH between 6.5 and 8, and a general hardness of 5–20 dGH. A moderate water flow is preferred.
Is Goldfish (Comet / Common) peaceful or aggressive?
Goldfish (Comet / Common) is classified as peaceful with an aggression score of 1 out of 10. They are generally well-suited to peaceful community tanks.
Can Goldfish (Comet / Common) live alone?
Yes, Goldfish (Comet / Common) can be kept singly or in a group. They are flexible and adapt well to both setups.
Does Goldfish (Comet / Common) have any special tank requirements?
Yes. Goldfish (Comet / Common) benefits from sand (sifters) and smooth gravel (sensitive barbels) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Similar Species
Guppy
Poecilia reticulata
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Gold Barb
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A highly active, peaceful schooling fish. The common 'Gold' variant is a captive-bred color morph (Schuberti) of the wild Green Barb. They are remarkably hardy and prefer slightly cooler sub-tropical water, making them excellent candidates for unheated indoor aquariums.
Paradise Fish
Macropodus opercularis
One of the first ornamental fish in the hobby (pre-dating the Goldfish in Europe). Paradise Fish are stunning, hardy, subtropical Anabantoids. However, they are notoriously aggressive, often exceeding the aggression of Bettas. They are cold-tolerant and thrive in unheated indoor aquariums, but they will readily attack smaller tank mates, eat fry, and fight conspecifics to the death.
Rainbow Shark
Epalzeorhynchos frenatum
A popular, active freshwater 'shark' (actually a cyprinid) known for its striking red fins contrasting with a dark or albino body. They are highly territorial bottom-dwellers. Only keep one per tank, as they are notoriously aggressive toward their own kind, other 'sharks' (like the Red Tail Shark), and similar-looking bottom feeders.
Cherry Shrimp
Neocaridina davidi
One of the most popular and hardy freshwater invertebrates in the hobby. They come in a rainbow of selectively bred colors. They are excellent scavengers and algae eaters, perfect for nano planted tanks. They are completely peaceful and have a negligible bioload, though they are highly vulnerable to predation by almost any fish with a mouth large enough to eat them.
Common Pleco
Hypostomus plecostomus
A heavily armored, nocturnal catfish famous for eating algae. However, they grow incredibly large, produce massive amounts of waste, and frequently outgrow standard aquariums. They require driftwood in their diet for digestion. As they age, they may become territorial or develop a taste for the slime coat of slow-moving, flat-bodied tank mates.