Comet goldfish
Carassius auratus
intermediate careOverview
The comet goldfish (Carassius auratus) is the classic long-tailed single-tail — a slimmer, faster, flashier version of the common goldfish, usually seen in bright orange or orange-and-white. It is a cold-water fish that grows to 25–30 cm+ and lives 15–20+ years. Comets are superb, athletic swimmers, which is exactly why they need so much room: this is a pond fish first and a tank fish only in very large aquariums.
Tank & water
A single comet needs 150 litres (40 gallons) minimum, and honestly belongs in a pond. Priorities:
- No heater: comets are cold-water fish — keep a stable 18–22 °C and let them cope with cooler outdoor temperatures.
- Serious filtration: as heavy-waste fish, they need over-sized filtration; a strong external filter is ideal.
- Length to swim: comets are speed merchants, so a long large aquarium or pond beats a tall, short one.
Feeding
Comets are omnivores. Offer a good sinking goldfish food, vegetables such as blanched peas and greens, and occasional live or frozen treats. Feed modest amounts once or twice daily and clear leftovers — these active fish will always look hungry, but overfeeding pollutes the water quickly. Regular maintenance and water testing keep them healthy.
Tankmates
House comets with other fast single-tailed goldfish — common goldfish and shubunkins are ideal companions. Their speed and boisterous feeding mean they will out-compete and stress slow fancy goldfish, so never mix the two groups. They are unsuited to tropical community fish, and being strong-swimming and long-lived they are a genuine multi-decade commitment rather than a casual first pet. A shoal of single-tails in a pond is the setup they were made for — size the group with how many fish in an aquarium.
Comets are also accomplished jumpers, especially when startled or when water quality dips, so an outdoor pond should have enough freeboard and an indoor tank a secure lid. Given room, cool clean water and company, a comet is one of the hardiest and most rewarding fish you can keep.
Comet goldfish — frequently asked questions
How big do comet goldfish get?
Comets reach 25–30 cm or more including their long, flowing single tail, and they are strong, fast swimmers. They need a great deal of space — see how big do goldfish get — which is why a pond suits them far better than any tank.
Do comet goldfish need a heater?
No. Like all goldfish, comets are cold-water fish that do best at 18–22 °C and happily overwinter in ponds. A heater is unnecessary; steady cool water and strong filtration matter far more.
Can comet goldfish live in a tank?
Only a very large one. A single comet needs at least 150 litres, and their speed and eventual size mean most tanks feel cramped. They truly shine in a pond where they can swim at full pace.
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