Best Way To Care For A Telescope Goldfish

Alison Page

Alison Page


Best Way To Care For A Telescope Goldfish

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If you enjoy the spectacular finnage and wide range of colors that are offered by fantail goldfish, you might want to consider adding a telescope goldfish to your collection.

In this guide, we give you all the information you’ll need to successfully keep and breed these beautiful freshwater fish in a home aquarium setup. But first, let’s find out more about the origins of this unusual and attractive coldwater species.

Telescope Goldfish

Telescope goldfish origins

Recent research suggests that modern goldfish are descended from wild carp, originating in parts of Asia and Siberia. These wild fish inhabit stagnant and slow-moving waters, especially ponds, ditches, and lakes, and small rivers, where they feed on vegetable matter, insects, small crustaceans, and detritus.

In the 1500s, goldfish were traded by China to Japan, appearing in Europe in the 1600s and in America by the 1800s. Most of the wonderfully diverse and colorful fancy varieties of goldfish that are enjoyed by hobbyists today were developed by Asian Breeders, specifically in China.

The telescope goldfish is one of over 125 captive-bred varieties of the fantail.

What is a telescope goldfish?

Telescope goldfish, scientific name Carassius auratus, is thought to originate from China, where they were first developed in the early 1700s. This unusual variety of fantail was once called the Dragon Eye goldfish or Dragonfish. However, in later years, the Japanese christened the fish Demekins, and that’s what telescope fish are still called today.

The telescope goldfish is a variety of fancy goldfish, having a rounded or egg-shaped body. The fish’s body is short with a wide head and split tail (caudal) fin of moderate length or, in some cases, long and flowing as in the veil tail, butterfly tail, and broadtail.

The telescope goldfish is known for its large, protruding eyes that are set on the end of long cone-like stalks, which are mounted on the sides of the fish’s head. In some cases, the stalks can extend to 3/4 of an inch. In juvenile fish under six months of age, the eyes appear normal in size, and the telescope effect does not begin to fully emerge until the fish matures.


One reason that the telescope goldfish is so popular is that it comes in many beautiful colors, including:

  • red
  • blue
  • chocolate
  • white
  • tri-color
  • bi-color
  • calico
  • red and white
  • black and white (known as the panda telescope goldfish)

There is also a rare and much sought-after coloration of chocolate with orange pom-poms.

These stunning fish can be found in both metallic and nacreous scale types, although they are rarely seen in a matte scale type.

Black moors

The black moor is also known as a black demekin in Japan and is sometimes called the black telescope goldfish.

The black moor is similar in looks to the telescope goldfish, but their eyes are not as prominent, and their scales are mostly matte black. Moors are considered to be easier to keep than telescope goldfish, as they are hardier, less prone to eye problems, and can live at lower temperatures.

Best Way To Care For A Telescope Goldfish

Care of the telescope goldfish

Big-eyed goldfish do not live in a wild environment, being exclusively captive-bred and usually kept in aquariums. So, you can create any kind of environment that you find aesthetically pleasing, as long as the water conditions are suitable.

Water conditions

Goldfish are notoriously dirty fish, and you will need an efficient filtration system to cope with the amount of waste they produce. Also, you must carry out a 30% water change every week to keep the water fresh and clean. Fancy goldfish of all varieties prefer a still water habitat. If the current is too strong, the fish will find swimming difficult and may become stressed.

Goldfish are coldwater fish, so you won’t need to install a heater in your tank. If you are keeping goldfish in an outdoor pond, don’t worry about them in the winter when the temperature drops. Goldfish are pretty hardy and will simply hide in the depths of the pond among plant roots and debris, surviving even when there’s ice on the pond’s surface.

The ideal water temperature for aquarium-kept goldfish is between 650 and 720 Fahrenheit. pH levels should be in the range of 6.0 to 8.0, and water hardness range 5 to 19 dGH. Although they are usually found in freshwater, goldfish can also tolerate a slightly brackish environment, provided that salinity is kept below 10%.

Tank size

Telescope eye goldfish typically grow up to five inches long in size, although they can get much larger than that. If conditions are ideal, a telescope goldfish can reach an impressive size of eight inches. Fancy goldfish grow steadily for the first few years of their life, so it’s wise to start off with a large tank, rather than using a small tank that the fish quickly outgrow.

A 10-gallon aquarium is the absolute minimum size that you should use for keeping fantail goldfish. Ideally, you want to start with a 20 to 30-gallon aquarium, increasing the volume by ten gallons per additional fish. However, you must make sure that you upgrade the tank in line with the fish’s growth.

When it comes to tank size and shape, a long tank is the best choice. All varieties of fantail goldfish are not terribly agile swimmers, and very deep, tall aquariums mean that the fish may struggle to get to the surface to feed. Also, a large water surface area makes it less likely that the fish will suffer from oxygen deprivation. Long tanks have more surface area than tall tanks or bowls that are narrower toward the top.

How many goldfish?

All variations of fancy goldfish, including telescope eye goldfish, fantails, and black moor goldfish, all need plenty of space.

The fish that you buy from your local fish store are juveniles. You should allow one inch of fish per gallon of water in the aquarium for these young specimens. However, as the goldfish grow and mature, they use more oxygen, and a lack of space will cause stunted growth and a failure to thrive. The stress that causes could predispose the fish to disease, even causing death in some cases.

So, providing as much swimming space as possible should ensure that your fish grow well and remain healthy.

Aquarium decoration and planting

You can include lots of plants in your aquarium. Not only do live plants look great, but they are also known to oxygenate the water and extract harmful nitrates. However, in a goldfish aquarium, it’s best to avoid using plants that float on the surface of the water, as that will prevent the fish from feeding.

Telescopes and other types of fantail and fancy goldfish need plenty of clear swimming space in the aquarium. These fish are poor swimmers who will struggle to cope with too much obstruction and dense planting. Plants should be positioned toward the rear of the aquarium, and any overgrowth must be pruned back to prevent the fish from becoming trapped among the leaves.

Carassius auratus are serial diggers, so, you’ll need to use plant weights to anchor any live plants that you include in your aquascape. If you prefer to use artificial plants, choose silk rather than plastic. Plastic plants can be sharp, potentially injuring your fish.

When choosing aquarium decoration, avoid including anything that has sharp edges or rough surfaces that could inflict injury on your fish’s protruding eyes or trailing finnage.

Gravel substrate creates a natural-looking environment for your display tank, and the fish will enjoy rummaging through the gravel in search of scraps of food. However, as these are very dirty fish, you should keep the gravel relatively shallow, and be sure to clean it thoroughly with an aquarium vacuum cleaner to remove excess fish waste.

Although you don’t need to illuminate your aquarium, lighting helps to bring out the colors of your collection, making calico, orange, and panda variations really pop.

Feeding and diet

Telescope eye goldfish, like all goldfish varieties, are omnivorous. That means that they eat a mixture of plant matter and meaty foods too. If you have algae in your tank, you may find that the goldfish graze on some species. Certain plants are also palatable and will be nibbled on by the fish.

You can achieve a good balance of foods by feeding your fish high-quality goldfish flake foods or pellets, as well as a serving of frozen or fresh food per day. When choosing dry foods, make sure that the food is formulated specifically for fancy goldfish. Round-bodied varieties of fancy goldfish are prone to swim bladder problems that are caused by constipation, which is often caused by feeding unsuitable dried foods. However, including fresh or frozen food in the diet helps to keep the goldfish’s digestive system moving, counterbalancing the effect of the dried food.

Freeze-dried foods are also good to feed to fancy goldfish. However, you should always soak the food in a little tank water to rehydrate the food before feeding.

Meaty foods to offer your fancy goldfish include:

  • bloodworms
  • brine shrimp
  • daphnia
  • tubifex worms

Although telescope eye goldfish do enjoy live food, be very careful to source your supply from a reputable store. Sometimes, live food can come with parasites or bacteria that could harm your fish, and on balance, it’s better to use frozen or freeze-dried products.

You can feed your goldfish twice or even three times per day. Be sure to allow your fish at least five minutes to eat the food. Their protruding eyes mean that telescope eye goldfish have poor vision and don’t always see the food straight away, so they take longer to feed than faster fish with better eyesight


All goldfish species are peaceful and gregarious, preferring to live in a community of their own kind.

The species’ poor vision can mean that big eyes goldfish sometimes can’t compete for food with their speedier tankmates, failing to thrive as a result. Also, telescope eye goldfish will struggle to compete for food with faster, more agile tankmates. For that reason, Carassius auratus is best kept with similar types, such as the black moor, lionhead goldfish, celestial goldfish, and bubble eye goldfish.

Fantails are notoriously slow and clumsy swimmers, largely thanks to their flowing fins. For that reason, it’s best to house them with other fantails or peaceful species that won’t chase or harass the big eye goldfish. Species that are confirmed fin nippers should also be avoided.

If you plan on using shrimp to control algae in your tank, be sure to buy large species of invertebrates that won’t end up as lunch for the goldfish. Snails make good tankmates, although they may eat some species of living plants.

Diseases and lifespan

Telescope eye goldfish can live for an average of ten to 15 years. However, in well-maintained home tanks and garden ponds, a lifespan of 20 years or more is not uncommon.

Although goldfish with big eyes are generally hardy, their eyes can cause them problems, such as poor vision and vulnerability to infection and injury. However, the most common cause of illness in fancy goldfish is bacterial infections that are predisposed by poor water conditions.

If only one fish is affected, it’s best to remove it to a quarantine aquarium for treatment, returning the invalid to the main tank once the fish has been disease-free for at least five days. As a side-note, always take great care when netting telescope eye goldfish, as it’s very easy to cause injury to the fish’s protruding eyes if they become snagged on the net. To avoid that problem, choose a net with a very fine gauge mesh.

The common bacterial goldfish diseases and parasites listed below that may affect telescope eye goldfish are usually easily treated with a proprietary antibacterial product that you’ll find in online .com shops and in most fish stores.

Bacterial diseases


Dropsy is a bacterial infection that attacks the fish’s kidneys. As a result, fluid accumulates within the fish’s body, causing the fish to become bloated and its scales to stick out, giving the appearance of a pinecone. Dropsy is usually fatal if not treated promptly.

Fin rot

Poor water conditions and physical damage caused by fin nippers in the community tank are the most common causes of fin rot. The condition presents as it sounds, with the affected fish’s tail and fins appearing ragged and torn.


Fish fungus looks like fluffy white growths on the fish’s skin and often accompanies other goldfish diseases.


Parasites can be introduced to aquariums via plants, live food, and new fish.

Anchor worm

Anchor worms appear as threads coming out of the fish’s skin. The worms burrow into the fish’s skin, lay eggs, and then die, leaving a hole that can become infected.

Ich (white spot disease)

Ich is a very common fish disease that is usually caused by poor water conditions and/or stress. The fish is covered with tiny white spots, affecting the body, fins, tail, and gills. The goldfish flicks its body against the substrate and tank decorations in an effort to get rid of the parasites.

Ich is treatable by using proprietary medication that you add to the tank water.

Fish lice (Argulus)

Fish lice are tiny, flat crustaceans that attach themselves to the fish’s body. Again, treating the whole tank with an over-the-counter product available in your local fish store will kill the lice.

Skin flukes

Skin flukes are tiny flatworms that attach themselves to the gills or body of the goldfish by means of hooks around their mouth. If your fish has skin flukes, you’ll notice red or black nodules beneath the skin. Flukes can be fatal if not treated quickly.

Other goldfish diseases

Cloudy eye

Cloudy eye commonly affects telescope eye goldfish and is usually caused by poor water quality, inadequate nutrition, or rough handling.


Constipation is a common condition in all variations of round-bodied goldfish and comes from poor feeding. Constipated fish show swelling of the body and poor appetite. Usually, starving the fish for 24 hours, and then offering live or frozen food cures the problem.

Swim bladder disease

Swim bladder problems are another common health condition that affects telescope eye goldfish. Affected goldfish show abnormal swimming patterns, sometimes floating to the surface, becoming trapped on the substrate, or swimming on one side.

The causes of swim bladder disease include constipation, poor diet, parasitic infection, or physical deformity. The condition can be treated with a specific medication that you’ll find at .com stores or in your local aquarium supplies store.


Ulcers on the fish’s skin are caused by wounds that develop fungal or bacterial infections. Once the root cause of the ulcer has been treated, the skin will heal.

Breeding Carassius auratus

Blackmoor and telescope eye goldfish spawn readily in a tank or pond setting, provided that the water conditions are right.

Gender differentiation

Sexing goldfish is virtually impossible when they are juveniles, although the male is generally slimmer and smaller than the female. However, the differentiation between the sexes of mature fish is easier during the breeding season.

The male develops white prickle-like structures on the head and gill covers, and when seen from above, the female goldfish appears fatter if she is full of eggs.

Breeding conditions

Telescope eye goldfish are egg layers. In the wild environment, goldfish spawn when the water warms up. So, to encourage spawning in the aquarium, you will need to replicate their natural conditions.

The tank must be at least 20 gallons, and the fish should be healthy, thriving, and free from disease. Many breeders separate the male and female fish a week or two to help increase their interest in spawning. The spawning tank should be heavily planted and must have solid surfaces too that the eggs can be laid on. If you prefer, you can use artificial, silk plants or fibrous spawning mops.

Spawning can be induced by gradually reducing the tank temperature to around 600 Fahrenheit, and then slowly warming it at a rate of 30 per day until the fish begin mating, usually when the temperature reaches 680 to 740 Fahrenheit. Carry out partial water changes of around 20% per day.

Also, feed the fish a variety of quality, protein-rich food, including worms and brine shrimp at this time to encourage spawning.

Spawning process

Telescope eye goldfish can continue spawning for several days, during which time the male fish chases the female around the tank, pushing her against plants and gyrating from side to side. Eventually, the female lays her eggs, which are then fertilized by the male. The eggs stick to smooth surfaces or plant leaves. The spawning process can last for several hours, during which time the female may lay up to 10,000 eggs.

Unfortunately, goldfish tend to eat their eggs. So, it’s best to remove the parent fish following spawning. The fertilized eggs typically hatch after four to seven days, depending on the water temperature. The fry will be swimming free immediately after hatching and should be fed specialty fry foods until they grow big enough to cope with flakes or brine shrimp. Alternatively, offer the fry the same diet as the adults but crush the food so that it is small enough for the youngsters to eat.

Juvenile telescope goldfish are generally black or dark brown in color so that they are camouflaged. However, after a few months, the fish will develop the adult coloration of orange, white, red, etc. Once the fry has grown to about one inch in length, they can join the adult tank.

Black moor


Telescope eye goldfish are readily available in most aquarium stores. However, you may need to shop around to find the more unusual colors and forms, such as butterfly, examples of these popular pet fish.

An online search of .com suppliers will probably bring up breeders in China who produce show-quality examples of telescope eye goldfish, including panda telescope, butterfly calico, solid orange, red, and just about every other color between. To place an order, you’ll need to email the breeder’s website to check what color and form of telescope eye goldfish they have available.

If you don’t want to wait for the fish to grow, you can order large examples, although they will be more expensive.


In this part of our guide to telescope eye goldfish, we answer some of your most frequently asked questions.

Q: How long do telescope goldfish live?

A: Telescope eye goldfish can live for between 10 15 years, although many can even live to reach 20 years old if kept in suitable tank conditions and given the correct diet.

Q: Can telescope goldfish live in a bowl?

A: Goldfish need good water quality, well-oxygenated water if they are to thrive. The main issue with goldfish bowls is that they have a very small water surface area. That means that oxygenation is typically poor, which can cause health problems for the fish.

Also, round-bodied goldfish fare better in a rectangular tank that provides a more open swimming environment that has plenty of open water space available.

Q: What is the big-eyed goldfish called?

A: The scientific name for a big-eyed goldfish is Carassius auratus. However, you’ll also see the fish advertized as telescope eye goldfish. The black moor is often referred to as a telescope but is actually a different variety of goldfish.

Q: Why do black moor goldfish have big eyes?

A: Black moor goldfish are not born with their distinctive huge eyes. That unique feature develops as the fish matures. Did you know that telescope goldfish’s eyes can only move sideways, not upward?

In summary

Telescope eye goldfish are a variety of fancy goldfish that are distinguished by their eyes, which protrude from the sides of the fish’s head. Telescopes have poor eyesight, and their conformation leaves them vulnerable to sustaining eye injuries. For that reason, these popular fishy friends do not make the ideal pet for a beginner hobbyist.

These omnivorous, coldwater fish are best kept in species-specific large aquariums with plenty of open water swimming space and highly efficient filtration to keep the water clean.

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