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
Water Parameters
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
Goldfish (Comet / Common) Care 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. To replicate their natural habitat, the tank should include sand (sifters) and smooth gravel (sensitive barbels).
Goldfish (Comet / Common) can be kept singly or in a group, making them flexible additions to most setups. Keepers should be aware that this species may uproot or eat live plants. 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.
Similar Species
Guppy
Poecilia reticulata
One of the most iconic and widely kept aquarium fish. Renowned for their incredible colors, hardiness, and prolific breeding. As livebearers, they give birth to fully formed, free-swimming fry. Males constantly pursue females for mating; therefore, a ratio of at least 2 females per male is strongly recommended to disperse stress.
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.
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.
Sparkling Gourami
Trichopsis pumila
A stunning nano species known for its iridescent blue/green eyes, body spots, and ability to make audible 'croaking' sounds. Unlike many anabantoids, they are social and best kept in groups. However, they are efficient micropredators that will hunt shrimp fry and pests like hydra. Requires stable water parameters and dense planting.
Bronze Corydoras
Corydoras aeneus
A highly popular, peaceful schooling catfish known for its armor-like scales (scutes) and active bottom-feeding behavior. They are essential clean-up crew members but require a dedicated sinking diet (not just leftovers). Sand substrate is strictly required to prevent erosion and infection of their sensitive barbels. They are 'gut breathers' and will occasionally dart to the surface to gulp atmospheric air.
Freshwater Angelfish
Pterophyllum scalare
The most iconic South American Cichlid, known for its distinct arrowhead shape and majestic fins. While domestic strains are hardy, they remain cichlids: they are semi-aggressive predators that will eat any fish small enough to fit in their mouths (like Neon Tetras). They form loose shoals as juveniles but pair off and become territorial as they mature. Height is more important than length for this species.