Comet Goldfish
Carassius auratus
Cyprinidae
FishDifficulty: ●●●○○Data: well-established
About
The comet is the long-tailed single-tail goldfish sold cheaply as a first fish and, more often than not, condemned to a tank a fraction of the size it needs. It differs from the common goldfish only in its slimmer body and deeply forked tail, and it grows just as large: single-tail goldfish pass 30 cm and stay fast, powerful swimmers all their lives. In a pond a comet lives well beyond a decade and spawns every spring; in a 60 L tank it stunts, sickens on its own waste and dies young.
Care
Treat this as a pond fish. Indoors one comet needs 300 L over a 150 cm footprint, unheated at 16–21 °C, with heavy filtration and strong surface agitation. It will uproot soft plants and can swallow anything small enough to fit in its mouth.
Diet
Opportunistic omnivore grazing plants, algae, detritus and small invertebrates; feed sinking pellets or gel plus blanched vegetables, and keep portions small — overfeeding drives both the waste output and the swim bladder trouble.
Tankmate compatibility
Possible with care (38)
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Avoid (233)
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Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Telling males from females
What works for this species, most reliable first.
- Breeding tuberclesStrong · only in breeding condition — they vanish out of season
Goldfish and their cyprinid relatives grow small white bumps on the gill covers and leading pectoral rays when they come into breeding condition.
Frequently asked questions
- What tank size does a Comet Goldfish need?
- A Comet Goldfish needs an aquarium of at least 300 litres (79.3 US gallons) with a footprint at least 150 cm (59.1 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Comet Goldfish need?
- Comet Goldfish does best at 4–26 °C (39.2–78.8 °F), pH 6–8 and a general hardness of 6–25 °dGH.
- What group size does a Comet Goldfish need?
- Comet Goldfish is a social species — keep a group of at least 3 so natural behaviour emerges and stress stays low.
- Is the Comet Goldfish suitable for beginners?
- Comet Goldfish sits in the middle of the difficulty scale — manageable for a careful beginner who has done the reading, but it has specific needs worth researching first.
Sources
Water & tank
Temperature4–26°C
Optimal temp.16–21°C
pH6–8
Hardness (GH)6–25°d
Carbonate (KH)4–15°d
Adult size30 cm
Min. volume≥ 300 L
Min. tank length≥ 150 cm
Group size≥ 3
Swimming zoneAll levels
TemperamentPeaceful
Water typeFreshwater
FlowModerate
Lifespan~15 yrs
Try in the calculator