Telescope eye Goldfish: Complete Guide to Care, Types, and Diseases

If you are an aquarium enthusiast looking for a fish with an extravagant and unique appearance, the Telescope Eye Goldfish (Carassius auratus), also known as Telescope Goldfish or Demekin Goldfish, is undoubtedly a fascinating option. Famous for its characteristic protruding eyes that give it its name, this pop-eyed fish requires specific care due to its particular anatomy and limited vision.

In this complete guide, we provide updated information on the different types of telescope eye goldfish, including the popular Black Telescope Goldfish (or Black Moor) and the Calico Telescope Goldfish, their proper feeding, how to prepare their aquarium, reproduction, essential care, and the most common diseases, paying special attention to the eye problems of the telescope goldfish.

Characteristics of the Telescope eye Goldfish

Taxonomy of Telescope Goldfish

Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Genus: Carassius

Scientific name: Carassius auratus auratus

Common Spanish names: pez telescopio, pez ojo de telescopio, goldfish telescopio, pez dorado de ojos telescópicos

Common English names: Telescope Eye Fish, Telescope Eye goldfish, Demekin goldfish, Dragon Eyes, Moor goldfish.

Origin of the Telescope Goldfish

Various scientific publications indicate that this variety of goldfish was developed in the 1700s in China, where it is known as “Dragon Eyes” or “Dragonfish”. It was later brought to Japan, where it is known by the name “Demekin”.

Komiyama et al. (2009) report that Japanese goldfish originated from one of the two groups of Chinese crucian carp “Gibelino” (Carassius auratus gibelio), and that the development of the Celestial Eye and Telescope Eye goldfish were independent events, indicating that these fish underwent strong artificial selection.

Currently, telescope goldfish are distributed worldwide through the aquarium trade.

Characteristics of Telescope eye Goldfish

With the exception of their prominent eyes, the body of the telescope goldfish is similar to that of the Fantail or Ryukin goldfish: short, rounded, or egg-shaped (ovoid), with a high back (dorsal contour) and fins that can be long and flowing (veil type) or shorter. The most distinctive feature is their eyes, which protrude noticeably from the head (up to 20 mm in some cases) and can be conical or rounded in shape.

It is important to note that the fry (juveniles) are born with normal eyes, and these begin to protrude at approximately one month of age, potentially taking three months or more to fully develop. The adult size of telescope goldfish usually ranges from 15-20 cm (6-8 inches) in body length, not including the caudal fin (tail fin), although this largely depends on the quality of care and available space. They are relatively slow and somewhat clumsy swimmers due to their body shape and limited vision.

Telescope goldfish are distinguished by:

• The fish’s large eyes, which look like two telescopes attached to its head.
• They have a long tail that fans out and flows in the water.
• Currently, there is a wide variety of these fish sold in aquarium stores.
• These fish can live for an average of 10 to 15 years.
• In terms of color, telescope eye goldfish display a wide range of colors including orange, yellow, white, red, black, or a combination of colors, resulting from selective breeding.

If you are interested in learning about the genetic basis of morphological diversity in domesticated goldfish, you can review the study by Kon et al. (2020), the link to which can be found in the references section.

How can you differentiate male from female telescope goldfish?

Telescope goldfish do not exhibit visible morphological characteristics that allow for easy differentiation between males and females; however, in Table 1, we present the main characteristics to differentiate them during the reproductive stage.

Table 01. Representative characteristics during the breeding season of goldfish.

Source: Thomas Book (2003), cited by Mondal et al. (2018).

Varieties of Telescope eye Goldfish

Black Moor Telescope Goldfish (Black Moor)

The Black Moor is a classic telescope variety that is popular among fish enthusiasts. With its distinctive black color and protruding eyes, it adds a unique touch to any aquarium.

The Black Moor telescope goldfish, or black telescope goldfish, has an elongated body with globe-shaped protruding eyes that extend telescopically from the head. This telescope goldfish variety can reach a size of up to 15 cm in length.

It is important to note that the Black Moor telescope goldfish may not maintain its color pattern throughout its entire life, as sometimes the color of its belly changes to a rust color with orange patches.

Panda Telescope Goldfish

The Panda Telescope Goldfish has a black and white color pattern and protruding eyes.

These fish can lose their panda coloration with age, changing to orange or white shades, or any combination of both.

White Telescope Goldfish

The White Telescope Goldfish resembles a golden goldfish. It can reach a length of 15 cm.

These fish can withstand higher temperatures and can coexist with other varieties of telescope goldfish.

Celestial Eye Telescope Goldfish

The Celestial Eye Telescope Goldfish, also called Chotengan, is a beautiful and unique telescope variety that is sure to catch the eye of any aquarium enthusiast. With its large, protruding eyes oriented upwards, with the pupils looking towards the sky (Komiyama et al., 2009), this fish is a stunning addition to any tank.

However, it is important to note that these fish require a bit more care than other varieties. They are sensitive to water quality and require a well-maintained tank to thrive. But with proper care, the Celestial Eye fish can be a beautiful and rewarding addition to your aquarium.

Bubble Eye Telescope Goldfish

The Bubble Eye Telescope Goldfish is a fascinating telescope variety known for its unique appearance. This fish has large, fluid-filled sacs under its eyes that give it a distinctive look.

However, these sacs can also be a disadvantage, as they are delicate and can be easily punctured. As a result, Bubble Eye fish require a gentle touch and careful handling. But for those willing to put in the effort, these fish can be a captivating addition to any aquarium.

How to Feed Telescope Goldfish?

A proper diet prevents digestive problems and promotes health.

• Type of Food: The base of their diet should be a high-quality commercial food formulated for goldfish, preferably sinking pellets. Floating foods can cause them to ingest air, contributing to swim bladder problems.
• Live Food: You can feed them live foods such as: Artemia (brine shrimp), insect larvae, water fleas (Daphnia), tubifex worms.
• Vegetable Component: It is crucial to include vegetables in their diet. You can offer them cooked, skinned, and chopped peas, blanched spinach, zucchini, etc., several times a week. This aids digestion. In this regard, Ahlam et al. (2019) reported that supplementing artificial feed with 7.5% pumpkin meal and 2.5% carrot meal improved the color intensity of telescope goldfish.
• Proteins: Supplement occasionally (1-2 times per week) with protein-rich foods such as brine shrimp, daphnia, mosquito larvae, or grindal worms (live, frozen, or freeze-dried from reliable sources).
• Frequency and Quantity: Feed small amounts that they can consume in 1-2 minutes, 2 or 3 times a day. They have small stomachs and a tendency towards overfeeding, which is harmful. Remove any uneaten food.

How Do Telescope Goldfish Reproduce?

Spawning Induction

Telescope eye goldfish reach sexual maturity in one to two years. The most common technique to breed telescope eye goldfish is to unexpectedly reduce the temperature to 11°C (52°F), and then gradually raise it at a rate of 2°C per day until spawning. Spawning generally begins when the temperature is between 20 – 23°C (68 – 73°F).

Another alternative is the use of synthetic hormones to induce reproduction in these fish. Mahadevi et al. (2018) recommend using the synthetic hormone WOVA-FH at doses of 0.7 ml/kg of body weight for males and 1.4 ml/kg of body weight for females to induce spawning of C. auratus auratus in captivity.

Meanwhile, Mondal et al. (2018) induced spawning in telescope eye goldfish breeders using Ovatide®, employing a dose of 0.5 ml/kg of body weight for females and 0.2 ml/kg of body weight for males, achieving high reproduction rates of around 93%.

Malik et al. (2024) found that Ovaprim™ at a dose of 0.7 ml/kg body weight for males and 1.4 ml/kg body weight for females was effective in stimulating reproduction in goldfish (Carassius auratus auratus) kept in captivity.

Courtship and Spawning

During courtship, the male telescope eye goldfish chases the female, continuously nudging her against the aquarium plants, which causes her to release her eggs. The spawning process can last several hours, during which the female can lay up to 10,000 eggs.

Once the female lays the eggs, you must remove the parents from the aquarium to prevent them from eating the eggs. The eggs attach to plants such as Cabomba or Elodea. The larvae hatch in 45 to 72 hours depending on the water temperature.

Upon hatching, the larvae are black or dark brown; after a few months, the fish will reach their adult coloration.

Care of Telescope eye Goldfish

Creating the right environment is crucial for the health and well-being of the telescope eye goldfish.

• Tank Size: Space is vital! An absolute minimum of 75 liters (20 gallons) is recommended for a single young telescope goldfish, but ideally more. To keep a group, plan for at least 40 additional liters (10 gallons) per adult fish. A long and wide tank is preferable to a tall one, with minimum recommended dimensions of 120 cm in length for a group of adults long-term.
• Filtration: Goldfish produce a large amount of waste (high biological load). You need a powerful filtration system, preferably an external canister filter oversized for the aquarium volume (e.g., if you have 100 liters, use a filter rated for 150-200 liters). However, the filter’s outflow current must be gentle, as they are weak swimmers. You can use a spray bar or direct the flow against the glass. An air pump with an airstone also helps with oxygenation.
• Substrate: Fine, smooth sand is recommended. Goldfish enjoy digging and foraging in the substrate. Gravel can be accidentally ingested or cause injuries. Avoid substrates with sharp edges.
• Decoration: Safety first! Due to their poor vision and prominent eyes, avoid any decorative objects with points, sharp edges, or roughness. Opt for smooth, rounded rocks and well-cured driftwood without splinters.
• Plants: Natural plants are beneficial. Hardy species like Anubias, Java Fern (attached to driftwood/rocks) are good options. Floating plants can help diffuse intense light. If using artificial plants, ensure they are silk or very soft plastic. Avoid hard, spiky plastic plants.

Water Quality for Telescope Goldfish Care

Table 02. Water quality parameters for the care.

Special Eye Care and Common Problems

The prominent eyes of the telescope eye fish are its most distinctive feature, but also its weak point.

• Poor Vision: They have very limited vision, making them prone to bumping into objects and being outcompeted for food by faster tank mates.
• Susceptibility to Injury: Their eyes can be easily damaged by sharp objects, unsuitable decoration, or even during aggressive interactions with other fish. An injury can lead to secondary infections.
• Eye Infections: They are prone to bacterial infections (like Popeye, where the eye swells even more) and fungal infections (cottony appearance). Poor water quality is a major risk factor.
• Other Problems: Cases of cloudy eyes or even shrunken eyes have been reported, often related to water quality, nutrition, or chronic infections.

Prevention is key: maintain excellent water quality, a safe aquarium without dangerous objects, and compatible tank mates.

Compatibility

Due to their slow swimming and poor vision, telescope eye goldfish should only coexist with other equally slow and peaceful fancy goldfish varieties.

• Ideal Tank Mates: Other Telescopes, Fantails, Ryukins, Orandas, Bubble Eyes, Celestial Eyes, White Cloud Mountain Minnows.
• Tank Mates to Avoid: Common Goldfish, Comets, Shubunkins (they are too fast and competitive for food), any aggressive or fin-nipping fish (like some Tetras or Barbs if kept in unsuitable conditions), Oscar fish, and Tiger Barbs.

Diseases Affecting Telescope eye Goldfish

Bacterial infections, fungal infections, parasites, and protozoa are common in telescope eye goldfish when kept in poorly maintained aquariums.

If you observe a sick telescope goldfish, it is best to treat it in a separate aquarium (hospital tank). This tank should not have gravel or plants, and the water should be changed frequently.

Some common diseases of telescope eye goldfish are:

• Dropsy: This is a bacterial infection of the kidneys in which fluids accumulate in the body, causing the fish to swell and its scales to protrude (pinecone appearance). Dropsy typically affects weakened fish and can be fatal if not treated quickly.
• Fish Tuberculosis: The fish looks emaciated and the belly becomes hollow; symptoms include lethargy, deformities, clamped fins, and more. Tuberculosis can be caused by overcrowding; there is no cure, and it can be fatal.
• White Spot Disease – Ich: Ich is a very common fish disease usually caused by poor water conditions and/or stress. Fish become covered with small white spots affecting the body, fins, tail, and gills.
• Cloudy Eye: Cloudy eye disease is a common ailment in telescope eye goldfish, and is usually caused by poor water quality, inadequate nutrition, or poor handling.
• Constipation: Constipation is a common condition in all variations of telescope goldfish and is a consequence of poor diet. Constipated fish show body swelling and lack of appetite. Usually, not feeding the fish for a day and then providing live food solves the problem.
• Swim Bladder Disease: Swim bladder problems are another common health condition affecting telescope goldfish. Affected fish show abnormal swimming patterns, sometimes floating to the surface, getting stuck at the substrate, or swimming sideways. Causes of swim bladder disease include constipation, poor diet, parasitic infection, or physical deformity. You can purchase medications at aquarium stores to treat this disease.
• External Parasites: External parasites are quite common in telescope goldfish but are often easy to treat. Among the parasites affecting these fish are flukes (trematodes), about 1mm long, which infest the gills or body of the fish. Another common type of parasite is the fish louse (Argulus sp.), a crustacean about 5 mm long that attaches to the fish’s body. Koyuncu (2021) recommends treating affected fish with trichlorfon: 0.25 mg/l at temperatures below 27°C (81°F) or 0.50 mg/l at higher temperatures).

Conclusion

Telescope eye goldfish are undoubtedly a striking and fascinating addition to any suitable cold-water aquarium. Although their care requires specific attention, especially regarding water quality, environmental safety, and tank mate compatibility, the reward is a beautiful fish with personality. By remembering their particular needs, such as feeding sinking pellets, providing a spacious tank, and preventing eye injuries, you can enjoy the company of your telescope goldfish for many years. We hope this guide is very useful for caring for your pop-eyed fish!

References

Ahlam, N. R., Lili, W., Hamdani, H., & Bangkit, I. (2019). Effect of adding pumpkin flour and carrot flour on changes in color intensity of goldfish (Carassius auratus L.) strain oranda. World News of Natural Sciences, 26.

Brough David. 2011. Telescope Goldfish: Demekin, Dragon Eye Goldfish, Globe Eye Goldfish. Animal World.

Komiyama, T., Kobayashi, H., Tateno, Y., Inoko, H., Gojobori, T., & Ikeo, K. (2009). An evolutionary origin and selection process of goldfish. Gene, 430(1-2), 5-11.

Kon, T., Omori, Y., Fukuta, K., Wada, H., Watanabe, M., Chen, Z., … & Furukawa, T. (2020). The genetic basis of morphological diversity in domesticated goldfish. Current Biology, 30(12), 2260-2274.

KOYUNCU, C. E. (2021). The First Record of Argulus japonicus Thiele, 1900 Infestations on Telescope fish (Carassius auratus) of Mersin in Turkey. Advanced Underwater Sciences, 1(1), 16–20.

Mahadevi, S. F., Antony, C., Bhosale, M. M., Gopalakannan, A., & Gnanavel, K. (2018). Induced breeding of telescopic eye gold fish (Carassius auratus auratus) using synthetic hormone (WOVA-FH).

Malik, A., Singh, D., & Punia, N. (2024). Effect of Synthetic Hormone on Breeding Potential of Gold Fish (Carassius auratus). UTTAR PRADESH JOURNAL OF ZOOLOGY, 45(17), 240-246.

Mondal, A., Singh, P., Mondal, M., Singh, M., Tripathi, G., & Tripathi, G. S. (2018). Comparative study of gold fish (Carassius auratus) breeding via induced and natural breeding. International Journal of Chemical Studies, 6(6), 1940-1944.

Page Alison. 2021. Best Way To Care For A Telescope Goldfish. Aquariadise

Pickrell Jeremy. 2023. Telescope Eye Goldfish: Care, Basic info, Photos & More. Hepper.

Woods Robert. 2021. Telescope Goldfish Care & Species Profile. Fishkeeping World.

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.