Comet Goldfish Care, Feeding,  Diseases, Breeding and more...

Introduction

Last Updated: 01-07-2025 by Grant Lord.

Comet Goldfish General Care Guidelines

Comets require no special care.  They are hardy, active fish.

• Give them enough room to grow; allow about 140 liters (30 gallons UK, 36 gallons US) with a filter installed for an adult fish.
• Make frequent large water changes, ensuring no large differences in water temperature or pH, and chlorine or chloramine has been removed from the water.
• Feed them a variety of fresh plant and animal-based foods.
• Comets are suitable for ponds.  
• These Goldfish rarely suffer from digestive problems caused by poor food, which can lead to balance problems in the more developed varieties with short, round bodies.

Comet History and Origin

All Goldfish varieties can be traced back to the Prussian or Gibel carp.  Through selective breeding of fish that developed odd genetic characteristics such as gold coloration and twin tails, all 100 plus different varieties have been created.

All Goldfish varieties have the same scientific name of Carassius auratus auratus var., not Carassius gibelio, which is interesting because no variety of Goldfish lives in the wild (unless introduced intentionally), not even the Common Goldfish.

The Comet goldfish is believed to have been a mutation of Ryukins or red Fantails.  It would have taken some serious selective breeding to achieve the slim body shape and crimson coloring from such a mutation.

It is thought to have originated about 1880 in US Government ponds on the Mall in Washington D.C.

A pioneer American breeder, Hugo Mulertt, may have produced them at about the same time.  It was he who gave the Comet its name.

Physical Characteristics

What Should a Comet Goldfish Look Like?

The body shape is similar to the Common Goldfish or Prussian carp but should be even slimmer.  The fins should all be longer than the Common Goldfish, and the caudal (tail) fin should be the same length as the body or longer.

The color change from drab, wild coloration to gold starts quite quickly at about a month old. 

Another variety often mentioned is the Sarasa Comet.  Sarasa is the Japanese word for calico.  This variety isn't colored the usual solid orange/red like most Comets but has a mix of red and white patches over the body and fins.

This color variation can occur in any metallic-scaled Goldfish, but breeders have managed to scatter the two colors more evenly across the body.

Scale Types of Comet Goldfish

The scale group is always shiny metallic.  Any fish with nacreous scales will be a crossbred specimen or is a Bristol Shubunkin if it has rounded caudal fin lobes, or an American/Japanese Shubunkin if it has pointed lobes.

Feeding and Diet

Tank Setup and Maintenance

Suitable Tank Size for Comets

Comets are active fish. 

Allow about 140 liters (30 gallons UK, 36 gallons US) with a filter installed for one adult fish.

140 liters is a good compromise between how big the fish will grow, how big the tank is to handle, water temperature swings, and the frequency of water changes needed to keep nitrates below 30 ppm.

For each additional Goldfish, another 45 liters (10 gallons UK, 12 gallons US) are required.

If your tank is for display purposes only, get a tank slightly taller than it is wide, as taller plants such as Vallisneria can be grown, and a taller tank has a larger viewing area.

Do not place your tank where it will receive direct sunlight or strong indirect sunlight.  Even strong artificial light can be a problem.  Tanks produce ideal algae growing conditions with their high nitrate levels; sufficient light is all that is necessary to produce an algal bloom.

If you have no option but to place your tank near a strong light source, you can always install a UV clarifier.

Maintaining Water Quality

Like all Goldfish varieties, the Comet requires good water quality to thrive.  The difficulty with this is that Goldfish can become large given the right conditions; when young, they need a lot of food to grow quickly, which produces large amounts of waste.

The ideal water parameters for Comets are:

• PH between 6.5-7.4
• Nitrates below 30 ppm (parts per million).  Very young fish (fry) require nitrates to be below 5 ppm.
• Ammonia needs to be at zero
• Nitrites need to be at zero
• Water temperature between 16-24^oC (60-75^oF)
• GH (general hardness) of 200 ppm or above (dGH 11)
• KH (carbonate hardness) of 143 ppm or above (dKH 8)

Most city water supplies fall into these parameters.  If your water source is from a bore, it will pay to check the water parameters, as nitrates and hardness readings can often be very high.

Some water supplies can be extremely soft, with KH 0-1 and GH 2-3.  If you want your fish to grow, the GH must be raised.

You will need a water test kit to check your water parameters regularly and determine when to make water changes.  Get a test kit that has test tubes and solutions.  Don't use test strips, as they are notoriously inaccurate.

Making partial water changes without checking whether they are sufficient or often enough is just guessing.

Filtration and Heating

A filter, although not essential, does reduce the maintenance workload.  Water changes must be made much more frequently to keep ammonia at a safe level if a filter is not installed.

Once it is cycled, a filter removes dangerous ammonia and nitrites, creating less harmful nitrates.  A water change becomes necessary once the nitrate level goes above 30 ppm, which is why you need a water test kit.

Comets are strong swimmers, a filter should turn the aquarium water volume over four times an hour but not create a current the fish have to swim against.

Comets are warm water fish, not cold water, not tropical, and prefer seasonal temperature changes.

Goldfish can take very low temperatures but only briefly, such as in Winter when they enter a dormant or low activity state.  Low water temperatures like these are best tolerated by less developed varieties such as the Comet. 

A heater is not required if kept indoors, where water temperatures will be well above freezing. If Comets are kept outside in a pond, and water temperatures are expected to fall below 0^oC (32^oF) for extended periods over Winter, bringing them inside for Winter would be wiser.

Plants and Substrate

Vallisneria is a suitable plant for a Comet aquarium or pond.

Goldfish are omnivorous, meaning plant material forms part of their diet.

If you choose the wrong plants, your Comets will strip them to stalks within hours.

Suitable plants are;

• Vallisneria - used as a background plant because of the height it grows to
• Blue Hygrophila – used as a foreground plant.  There is a dwarf variety available.
• Hygrophila Difformis – used as a foreground plant.  Its fast growth helps control algae.
• Red Bacopa – the leaves get a red tinge on the underside
• Ludwigia Arcuata – this plant requires a relatively large amount of light before forming a red stem and leaves.

Adding substrate or having a bare bottom tank is a personal choice, but there are some considerations before purchasing substrate;

• White substrate will cause your fish to lose color intensity
• Sand is not a good choice if you want to install an under-substrate filter.  The grains need to be between 3 and 6mm in size.
• Goldfish will choke on small pieces of smooth gravel.  I have lost two Black Moors from this.
• Are you planning on growing live plants?  Plants can be grown in containers if you don't want to have substrate.

Aquarium Decorations

Aquarium decorations aren't as problematic for Comets as it is for other shortsighted varieties, such as Moors, who tend to blunder around an aquarium.

Comets are quite active fish, so they appreciate more open water in the aquarium so they can move around freely.

Decorations with holes or confined spaces should also be avoided, as if it's possible to get stuck, Goldfish invariably will.

Suitable Tank Mates for Comets

The most common mistake novice Goldfish keepers make is to mix fancy varieties with single-tailed varieties.  They don't realize that slow-swimming varieties such as Oranda and fantails can't compete successfully with fast-swimming varieties like Comets for food.

What happens over time is as the single-tailed fish get the majority of the food, they get bigger and bigger, and the others don't thrive.

Comets can be kept with other Goldfish varieties, but a close watch needs to be kept on them to ensure they aren't getting more than their share of the food.

Plecos and Bristle Nose catfish used for removing algae can become a problem when they get larger if they start eating the slime off the sides of your Comet as a protein supplement to their diet.

Any other small fish or aquatic life in the aquarium will be eaten if it can fit into your Comet's mouth.

Health and Diseases

Parasites

Several types of parasites attack Goldfish;

• Flukes if the body length of the fish is under 52mm (2 inches)
• Intestinal worms
• Protozoan parasites such as Costia and Ich (white spot)
• Free swimming aquatic parasitical crustaceans such as anchor worm and lice.

Bacterial Diseases

Bacterial infections can show as;

• Fin rot
• Bacterial gill disease
• Mouth rot
• Pop eye
• Raised scales
• Body sores (ulcers)
• Red patches on the body and fins

Fungal Infections

Fungal infections are quite common in Goldfish.  They are usually seen as large or small tuffs of white cotton wool-like matter on the skin or fins.
A much more serious fungal infection is Branchiomyces, an aggressive fungus that kills fish by destroying gill tissue.

Viral Pathogens

The two most common viruses are:

• Lymhocystis virus, which appears as a white crusty growth on the skin and
• Papillomatous lesions caused by the cyprinid herpes or carp pox virus.

Both look very similar, but the treatment is different.  Both are weakly transmissible, but neither is fatal.

More about Goldfish diseases here...

Quarantining New Fish

Quarantining new fish does not mean keeping them separate from your existing fish population for a few weeks and observing if they develop a disease.

It is unlikely fish being kept in pristine quarantine conditions and being fed high-quality food will succumb to any disease.

But what if the new fish are carrying a few parasites, such as flukes within the gills, and do not exhibit any symptoms?

And what if your fish have low immunity to flukes as they have never been exposed to them before?

It should be assumed your new Comets have parasites and should be treated for them. 

A mild salt bath will take care of any bacterial or fungal infections that aren't obvious at the time of quarantining.

An additional benefit of salt is that it boosts Goldfish's immune system.

Breeding Comet Goldfish

Comets are one of the more straightforward varieties to breed because they lack features that hinder breeding in the more exotic varieties, such as telescopic eyes.  They are quite active fish, so a large aquarium or small pond is required.

Male/female differences are more obvious in the breeding season because of their slim body shape.  The female becomes much more rounded as the eggs ripen prior to spawning.

The white tubercles that appear on the male's operculum (gill plates) in the breeding season are usually easily seen, as are the tubercles on the leading edges of the pectoral fins, indicating the male is in breeding condition.

When Comets are bred, all fry will have metallic scales.  Any fish that hasn’t changed color by six months old shouldn’t be used as breeding stock.

Feeding large amounts of tubifex worms and bloodworms is also recommended, but finding enough supplies for these types of food can be problematic.

More about Goldfish breeding here...

Summary and Key Facts

Country of Origin: USA

Maximum size (body length): 200mm (8 inches)

Caudal Fin: Single, as long as the body, deeply forked with pointed ends

Dorsal Fin: Present

Anal Fin: Single

Scale Group: Metallic, intense red coloration is preferred.  Many have red and white coloration, but a single red/gold/orange color is desired for the specimens to be shown.

Eyes: Normal

Distinguishing traits: Extended fin length, with the caudal fin the length of the body.

Breeding:  One of the easier varieties to breed because they lack features that hinder breeding in the more exotic varieties such, as telescopic eyes or extended double caudal fins.  They are quite active fish, so a large aquarium or small pond is required.

Male/female differences are more obvious in the breeding season because of the slim body shape.  The female becomes much more rounded as the eggs ripen prior to spawning.

Special requirements: Nil

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