Comet

Identification

A comet is a common goldfish drawn out at both ends. The body is slimmer, the pectoral and pelvic fins are long and pointed, and the tail is the giveaway: a single, deeply forked fin with tapering lobes that, on a good fish, comes close to the body in length. At rest it trails like the comet’s tail the breed is named for; under acceleration it snaps flat and the fish becomes a spear.

Against the common goldfish, judge by tail length and fork depth, since the colours overlap completely. Against the shubunkin, judge by the scales: a shubunkin is calico on a semi-transparent ground, while a comet has metallic scales in one or two colours. All three want the same things, and all three are pond fish. Orange and red are the norm, yellow and white common, and the red-and-white sarasa the most sought-after pattern; young comets are often bronze and take most of a year to colour up.

Common, comet or shubunkin?

• 

  Common Goldfish

  A short tail

• 

  Comet

  A long, deeply forked tail

• 

  Shubunkin

  Calico, on see-through scales

Three single-tailed goldfish side by side: a common goldfish with its short tail ringed, a comet with its long, deeply forked tail ringed, and a shubunkin with its calico body ringed.

1. Common Goldfish. A short tail and a metallic shine.
2. Comet. Slimmer, with a long, deeply forked tail.
3. Shubunkin. The same outline, wearing a calico pattern on semi-transparent scales.

Photographs: Common Goldfish, ぱたごん, CC BY-SA 3.0; Comet, Yatokin, CC BY-SA 4.0; Shubunkin, Michelle Jo, CC BY-SA 3.0. Rings added.

The varieties

Few named forms, because the comet was bred for a shape rather than for ornament.

• Orange and red. The default, and what most ponds hold.
• Sarasa. Clean white with deep red patches, named from a Japanese word for patterned cloth. The most sought-after form and the one whose pattern is least settled in a young fish.
• Yellow and white. Less common, and a white comet shows every mark, which is worth knowing before buying one.
• Bronze. Not a variety. Young comets are wild-type olive-brown and colour up later; a bronze fish is simply one that has not yet, or one of the few that never will.

How it develops

Comets grow quickly, which is the source of much of the trouble they cause their owners. Most goldfish hatch bronze and lose the dark pigment during the first year; growth depends on food, space and water.

Growth is the thing that catches people. A five-centimetre comet bought in spring can need adult housing within a year, and how big do goldfish get covers what the finished fish looks like. Buying the final tank first is cheaper than buying two, and the tank size guide sets the figures.

Colour is the part nobody warns about. A tank of drab brown juveniles is the normal midpoint of a successful spawn, not a failure, and breeding goldfish covers why breeders cannot judge on colour for most of a year.

Choosing one

Comets are cheap, widely sold, and frequently sold from tanks you would not choose to buy from. Both facts matter.

1. Watch it move. A comet should be cruising, not hanging. Fins carried open, body straight, no listing.
2. Look at the tail. Even lobes, no permanent kink or fold, no ragged edges. A torn tail heals; a bent caudal peduncle does not.
3. Check for flicking against decor, which points at parasites — flashing and rubbing covers what that behaviour means.
4. Look at the whole system, not the fish. Feeder tanks and crowded display tanks share filtration, so one sick fish means the water carries it — choosing and bringing home a goldfish covers reading a shop.
5. Then quarantine, for at least four weeks, without exception. This is a breed where it matters, because comets are often held badly before sale. Quarantining a new goldfish covers doing it.

On feeder fish specifically: the fish is ordinary and the conditions are not. What you are buying is a normal comet with an above-average chance of arriving with ich or flukes, and a full quarantine turns that from a problem into a formality.

Where you will find one. Any general pet shop, and frequently in the same feeder tanks as commons, with the same warning attached. What varies is fin length and the evenness of the colour, and neither is visible at the 3 cm size comets are usually sold at — they show at 8 to 10 cm. If the finnage is what you are buying the fish for, buy a larger one and pay for it. Sarasa comets, the red-and-white ones, are the single variant where quality genuinely varies enough to be worth shopping around for.

Personality and behaviour

The comet is a fast, streamlined goldfish and behaves like it. It cruises constantly, darts the length of the tank for no obvious reason and usually reaches food before the slower fish have noticed. That energy is good company for commons and shubunkins and bad news for orandas, ranchus and other slow fancies, which go hungry in a comet’s tank; the compatibility checker flags the combinations that fail.

Comets are sociable and do best in a small group. In spring, males chase females relentlessly, which can leave the long tail frayed for a few weeks — is my goldfish breeding? covers why that looks so much worse than it is. They are also strong jumpers, particularly when new or startled at night, so a lid matters, and first aid for an injured goldfish covers what to do if one gets out.

Aquarium requirements

Think in length. A working range for adults is 150 to 200 litres (40 to 53 US gallons) for the first comet and 75 to 100 litres for each additional one, but a comet in a tall, short tank is worse off than one in a lower tank of the same volume. Many keepers of adults settle on 280 litres (75 US gallons) or more, or a tank at least 120 cm (4 feet) long, and beyond that a pond serves the fish better than any indoor setup. The tank size guide explains the reasoning and the pond guide covers the move outdoors.

Keepers commonly aim for filtration that turns the volume over five to ten times an hour; comets enjoy some current and will play in an outflow that would exhaust a fancy. Keep the water between 10 and 24 °C (50 and 75 °F) with gradual changes, change 25 to 50 percent weekly according to nitrate, and choose sand, a bare bottom or large smooth stones — substrate for goldfish covers grain size. Plants are eaten or uprooted unless tough, and plants for goldfish tanks covers the few that survive.

Feeding

Comets eat anything and beg for more. Base the diet on a quality pellet, floating or sinking, and add blanched vegetables, duckweed, gel food and frozen foods across the week. Feed small amounts one to three times a day, finished within a minute or two, and skip a day now and then; overfeeding a comet harms the water more than the fish. The feeding frequency guide gives a routine that scales with tank size.

In a pond, ease off as the water cools, move to a wheat-germ-based food below about 15 °C, and stop feeding when the fish stop taking food, usually around 8 to 10 °C — feeding through the seasons has the bands and a pond through the year the rest of the calendar.

Common health considerations

Comets are hardy, and most of their problems are mechanical or water-related. The long tail is easily torn on sharp decor, in spawning chases or by a jump into the lid; torn fins heal cleanly in good water but invite fin rot if the damage is repeated or the water is poor. Ammonia and nitrite in an undersized or uncycled tank show as gasping, red streaks and clamped fins, and are corrected with water changes rather than medication.

Ich, the white-spot parasite, is common in newly bought comets that have passed through crowded dealer tanks; quarantine new fish for at least four weeks, watch for salt-grain spots and flashing, and treat early. Pond comets can also pick up anchor worm, fish lice and flukes from new stock.

What goes wrong, in order

A hardy fish, so its problems are mostly housing and mechanics rather than disease.

What you see	Usually	Where to look
A frayed or split tail	Sharp decor, a jump, or the spring chase	Torn fins
Salt-grain spots after a purchase	Ich, from a crowded dealer tank	White spots
Gasping, red streaks, clamped fins	Ammonia or nitrite in an undersized tank	Red streaks
Found on the floor	It jumped, and there was a reason	First aid
Flicking against decor	Parasites, usually newly arrived	Flashing and rubbing
Worn snout, dull colour, glass-surfing	The tank is too short	Goldfish tank size

The last row is the one that is hardest to see, because nothing looks acutely wrong. A comet in a tank it has outgrown does not get ill; it gets diminished, and the signs read as personality rather than as a problem.

Is a comet right for you?

It suits you if you have a pond, or a tank at least 120 cm long, or intend to get one. It is hardy, forgiving of beginners’ mistakes, tolerant of a seasonal temperature swing, long-lived, and among the most rewarding goldfish to watch because it actually uses the space it is given.

It does not suit you if the tank is small, if it would share water with fancies, or if you want a fish that stays the size you bought it. A comet is a pond fish that tolerates aquariums, not the other way round, and goldfish ponds is the page that makes that argument properly.

And it is a decade-or-more commitment, which is the thing least often said about the cheapest fish in the shop. What keeping goldfish costs puts the rest of it in proportion.

History and origin

The comet was developed in the United States; the veiltail, fixed in Philadelphia in the 1890s, is the other well-known American breed. It appeared in the early 1880s, and the Cincinnati aquarist and author Hugo Mulertt is generally credited with developing and promoting it; some accounts also place early comets in government fish ponds in Washington, D.C., in the same decade. Whatever its exact beginnings, the fish was fast, tough and easy to breed in outdoor ponds, and within a few decades it was widely produced.

The red-and-white sarasa, named with a Japanese word for patterned cloth, is a prized form, and comets remain a staple of the pond trade in North America and Europe. Comets have a show standard in Britain and were once widely exhibited, though few are shown today; the appeal now is movement, hardiness and a tail that looks best in open water.