Black Comet Goldfish (Carassius auratus)

Choose a dark comet with a bronze glow

The Black Comet Goldfish is a dark form of the comet goldfish, Carassius auratus. It has the comet's slim body and long, deeply forked tail, with a deep brown-black back and head, warm bronze-gold tones along the lower flanks and belly, an amber eye and long, smoky fins. In a pond full of red and orange fish, a black comet adds depth and contrast, and in sunlight the bronze underside glows. It is hardy, quick and long-lived, and it stays outdoors all year in a well-kept pond.

Practical Fishkeeping defines a comet by its tail, not its colour: any goldfish with the comet tail is a comet, and a good one is forked and well spread, without drooping or overlapping lobes. Wikipedia's comet goldfish article, drawing on Johnson and Hess's Fancy Goldfish and Chris Andrews's guide, records that the comet was developed from the common goldfish in the United States in the 1880s and is slightly smaller and slimmer than its ancestor. The goldfish itself is native to East Asia, according to FishBase.

Do not confuse it with a black moor

Compare it with our Bronzed Comet Goldfish, browse the whole goldfish range, or read our comet goldfish guide for the differences between comets and fancy goldfish.

Understand that black colour can change

Black is the least predictable colour in goldfish. In a Practical Fishkeeping answer, Paul Green explains that black is not a dominant colour gene in goldfish and will often disappear over time, and that fish kept in warmer water tend to lose it faster. Wikipedia's telescope goldfish article describes the same thing in black telescopes, where young fish can lose black pigment as they grow. Some dark goldfish keep their colour for years; others turn bronze, gold or orange. We cannot promise that a Black Comet Goldfish will stay black, and a gradual change is a normal part of growing up, not a sign of illness.

Give the black its best chance

• Keep it cool: a pond, or an unheated aquarium for young fish, rather than warm water.
• Skip colour foods: Practical Fishkeeping advises avoiding colour-enhancing (red) foods if you want to keep black; feed a standard staple instead.
• Allow some sun: Practical Fishkeeping mentions direct sunlight as one method keepers use to hold black, and the OATA garden pond guide suggests about four to six hours of sun a day with some shade.
• Know stress black: goldfish can also gain temporary black after stress or treatment, which Practical Fishkeeping calls an outward sign of healing that lasts days or weeks.

Know what arrives: one 2–3 in comet

Each purchase supplies one live Black Comet Goldfish at 2–3 in, about 5–8 cm. It is a young fish with most of its growth ahead of it. Sex is not chosen or guaranteed. The depth of black and the amount of bronze vary from fish to fish, so the photographs show the colour form rather than the individual you will receive. The Maidenhead Aquatics fish database recommends keeping goldfish in groups, with mixed varieties if you like, so plan several fish rather than one.

Plan for a fish that is hard to spot

A dark fish in a dark pond is easy to lose sight of. Feed in the same place each day so the fish learn to come up, count them at feeding time, and mix in lighter fish such as bronze comets so the group is easy to follow. Keep a net handy for health checks, because problems are harder to see on a dark body. Read our delivery information before ordering.

Plan the space: pond first, tank as a stage

Comets grow large. OATA gives up to 30 cm as the most common maximum body length of pond goldfish, Practical Fishkeeping says comets reach 35 cm and regularly 30 cm, and FishBase records 48 cm total length for the species. OATA reports goldfish living up to 20 years in a healthy pond, and FishBase records a reported age of 41 years.

Choose the right route

To size a pond, the Maidenhead Aquatics pond guide suggests 25 cm of fish per 455 litres, counted at adult size. Three adult comets at 30 cm come to 90 cm of fish, which needs about 1,640 litres. Work out your volume with our tank volume calculator and check the whole stock with our stocking calculator.

Shape the pond with depth, shade and plants

Depth gives stable temperatures: OATA describes a cool zone at the bottom in warm spells and a warmer area in freezing winters, which matters for a fish whose black may fade faster in warm water. The OATA garden pond guide asks for at least 60 cm in some parts, a level site with four to six hours of sun, and some shade. Add shallow ledges for marginal plants and a mix of submerged and floating plants, which add oxygen, take up pollutants and give shelter. The Maidenhead Aquatics pond guide aims for about 33–50% of the surface covered. Keep the pond away from overhanging trees, or fit an autumn net.

Divide the pond by function

Set the water targets

Comets tolerate a wide range, but sources draw it differently: OATA gives pond fish 4–24°C, pH 6.5–8.5 and 8–18 dGH; Practical Fishkeeping says comets are happiest at 10–20°C in slightly hard, alkaline water of pH 7.5–8.5; and the Maidenhead Aquatics database gives pH 7.0–8.0 and up to 25 dH. The targets below satisfy all three.

Treat every top-up from the tap

OATA advises treating all new tap water with a conditioner to remove chlorine or chloramine. Check your water company's report for hardness and pH, compare the numbers in our water matcher, and read the water chemistry guide for what each test means. Test kits and conditioners are in our water care and treatment range.

Filter well and keep a routine

OATA says any pond holding fish needs a filter to stop toxic ammonia and nitrite building up, and that adding fish too fast causes new pond syndrome, when the filter bacteria cannot keep up with the waste. Run a new pond with conditioned water and working equipment for at least 24 hours before fish go in; a full fishless cycle takes several weeks, according to the OATA garden pond guide. Our nitrogen cycle guide explains the process.

Follow a weekly and seasonal checklist

1. Test ammonia, nitrite, nitrate, pH and hardness each week and note the results.
2. Clean filter media only in pond water when the flow from the outlet drops, as the Maidenhead Aquatics pond guide suggests.
3. In autumn, remove dead leaves and trim marginal plants before they rot.
4. In winter, keep part of the surface open with a pond heater or float, as OATA advises.
5. In spring, restart feeding slowly and watch closely for disease as the water warms.
6. Replace any UV bulb about once a year.

Feed small, plain meals by season

Goldfish are omnivores: FishBase records wild fish eating plankton, bottom-living invertebrates, plants and detritus, and Practical Fishkeeping says comets take a wide range of dried and frozen foods. For a dark comet, the main difference is to leave out colour-enhancing foods, which Practical Fishkeeping advises against if you want to keep black.

Build one measured meal

• Young fish: Tropical Super Goldfish Mini Sticks, small enough for a 2–3 in comet; OATA notes that pellet sizes should suit the size of fish.
• Adults in summer: a plain floating staple such as Tropical Pond Sticks Mixed.
• Cooling water: Tropical Koi & Goldfish Wheat Germ & Garlic, the lower-protein type OATA recommends.
• Portion: once a day, only what is eaten within a few minutes.
• Cold water: OATA says it may be better not to feed below 8°C; the Maidenhead Aquatics pond guide feeds wheatgerm only at around 10°C and normal food once the water stays above 10–15°C.

Other foods are in our fish food range.

Introduce it in the right season

The OATA garden pond guide advises against adding fish to a pond in winter, when their immune system is inactive. From spring to early autumn, follow OATA's floating-bag method: keep the bag out of bright light, float it for 10 minutes, add small amounts of pond water, then release the fish with as little bag water as possible. Our guide on how to acclimatise new fish covers each step. If the fish arrives in the cold months, grow it on in a mature, filtered aquarium of 100 litres or more: the Maidenhead Aquatics database suggests starting small comets indoors and moving them to a pond as they grow, and OATA says non-fancy goldfish can be moved to an outdoor pond.

Use a first-week checkpoint plan

Pick companions that match a fast single-tail

OATA advises against keeping comets with fancy goldfish, because comets swim faster and often outcompete them for food, and some boisterous fish nip the fins of fancies; Practical Fishkeeping gives the same warning about twin-tailed goldfish. Wikipedia notes that comets are often kept with koi, and OATA says most pond fish are compatible, though needs differ.

Screen each companion

Check a mix in our tank mates tool, browse goldfish and coldwater fish and our koi and carp, or read the cold water fish buying guide.

Check a dark fish closely for health signs

OATA lists the signs of a healthy fish as clear, bright eyes, undamaged fins, intact scales with no ulcers or bumps, normal swimming and steady breathing. Its watch-list includes hanging at the surface, sitting on the bottom, turning darker or paler than normal, faster or slower breathing, white spots or fluffy growths, lost scales or fins and loss of appetite. White spots stand out on a black body, but reddening is harder to see, so look at the fins in good light. Practical Fishkeeping advises against buying comets with visible blood in the fins.

Pair each sign with an action

Breed responsibly and keep it out of the wild

OATA says goldfish are the pond fish most likely to spawn, especially when males outnumber females and the temperature is right, and suggests a shallow, heavily planted area because adults eat eggs and fry. The Maidenhead Aquatics database gives 15°C and above for spawning chases and 48–72 hours for the eggs to hatch, and notes that young goldfish start out brown. Practical Fishkeeping describes white breeding tubercles on the gill covers of males and plump, lopsided females, and notes that comets cross freely with common goldfish and shubunkins.

No licence is needed to keep goldfish in England and Wales, according to government guidance. OATA states that releasing fish into the wild is illegal, and FishBase lists the goldfish as a potential pest where it has been introduced. Rehome surplus fish through another pond keeper or a local aquatic shop.

Answer Black Comet Goldfish buying questions

What is a Black Comet Goldfish?

It is a dark colour form of the comet goldfish, Carassius auratus: a slim, single-tailed goldfish with a long, deeply forked tail. Ours shows a deep brown-black body with bronze-gold tones on the lower flanks. It is a hardy pond fish.

Will my Black Comet stay black?

Not necessarily. Practical Fishkeeping explains that black is not a dominant colour in goldfish and often disappears over time, faster in warmer water. Many dark goldfish keep some black, others turn bronze or orange; we cannot guarantee the colour will last.

Is a Black Comet the same as a black moor?

No. A black moor is a twin-tailed fancy goldfish with telescope eyes, kept in aquariums. A black comet has a single forked tail, normal eyes and a slim body, and lives in ponds.

How big does a Black Comet Goldfish grow?

Usually to about 30 cm. OATA gives up to 30 cm as the most common maximum for pond goldfish, Practical Fishkeeping says comets grow to 35 cm, and FishBase records 48 cm for the species.

Can it live outside all year?

Yes, in a filtered pond at least 45–60 cm deep. Keep part of the surface free of ice in winter, and reduce or stop feeding as the water falls towards 8–10°C.

Can I keep a Black Comet in an aquarium?

Only while young, or in a very large tank. OATA asks for at least 100 litres for one adult goldfish plus 50 litres for each extra adult, and Practical Fishkeeping recommends a tank of at least 120 cm, ideally 150–180 cm.

Can it live with fancy goldfish?

It is better not to. OATA and Practical Fishkeeping both advise keeping comets apart from twin-tailed fancy goldfish, which are slower and lose out at feeding time.

How many fish come with one purchase?

One live Black Comet Goldfish at 2–3 in (about 5–8 cm). Sex is not chosen or guaranteed.

Consult the care references

• Practical Fishkeeping: Will my red, black and white goldfish lose the black colour with age? — why black colour in goldfish often fades over time, faster in warmer water, and how temporary stress black appears.
• Practical Fishkeeping: Comet goldfish — what makes a comet, sarasa colouring, adult size, pond and aquarium space, water, diet, companions and sexing.
• OATA: How to look after pond fish — UK guidance on pond fish water values, sizes, group sizes, pond volume and depth, seasonal feeding, winter care, health signs and breeding.
• OATA: How to set up and look after your garden pond — UK guidance on siting, building, maturing and stocking a garden pond, adding fish and keeping herons and otters out.
• OATA: How to look after goldfish in an aquarium — UK guidance on goldfish in aquariums: volume per fish, water values, weekly maintenance and keeping comets apart from fancy goldfish.
• Maidenhead Aquatics fish database (fishkeeper.co.uk): Sarasa Comet — sarasa comet size, temperature, pH, pond depth, companions, colour development, spawning and lifespan.
• Maidenhead Aquatics: Taking care of goldfish in a pond — pond stocking rule, filter cleaning, seasonal feeding temperatures, oxygen and plant cover for goldfish ponds.
• FishBase: Carassius auratus — native range, maximum length and age, water values, wild diet and the pest risk when goldfish are released.
• Wikipedia: Comet (goldfish) — history of the comet goldfish, its body and tail, colour forms including the sarasa, and lifespan (citing Johnson & Hess and Andrews).
• Wikipedia: Telescope (goldfish) — the black moor, a twin-tailed telescope-eyed goldfish, for comparison with a black comet.
• GOV.UK: Introduce or keep non-native fish — England and Wales guidance listing goldfish and ide or orfe among the non-native fish you can keep without a licence.
• Tropical Fish Co delivery policy — current dispatch days and Live Arrival Guarantee terms.