Telescope

Identification

Telescope goldfish are named for eyes that project outward from the skull on fleshy, cone-shaped mounts, so that from above the head shows two distinct bumps either side. The eyes may be globular, conical or flattened at the front depending on the line. Fry hatch with ordinary eyes, and the protrusion develops over the first year, so a small telescope may still look much like a fantail.

Behind the eyes sits a standard fancy body: egg-shaped, with a full dorsal fin and a double tail. Japanese demekin lines are often built on a deeper, ryukin-like body, while Chinese and Western lines tend to be rounder; butterfly telescopes carry a tail that spreads wide and flat when seen from above.

Colour is where the breed is most varied. Red, red-and-white, calico and chocolate are common, along with blue-scaled fish and the black-and-white panda pattern. Solid black telescopes have their own name, the black moor, though apart from colour they are very much the same kind of fish, and the British show standard judges the moor as a separate type.

Telescope, celestial or bubble eye?

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  Telescope

  Eyes pushed out to the sides

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  Celestial Eye

  Eyes turned to the sky

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  Bubble Eye

  A sac beneath each eye

Three eye breeds side by side: a telescope with an eye projecting from the side of its head ringed, a celestial seen from above with an upturned eye ringed, and a bubble eye with the fluid sac beneath its eye ringed.

1. Telescope. Eyes that project outward from the sides of the head. The black moor is the black form of the telescope (the British show standard judges it as a separate type).
2. Celestial Eye. No dorsal fin in the standard, and eyes turned upward to gaze at the surface, with no sac beneath them.
3. Bubble Eye. No dorsal fin in the standard, upturned eyes, and a fluid-filled sac beneath each one that trembles with every movement.

Photographs: Telescope, Fanghong, CC BY 2.5; Celestial Eye, Michelle Jo, CC BY 3.0; Bubble Eye, Lerdsuwa, CC BY-SA 4.0. Rings added.

The varieties

One breed, several names, and the names describe different things.

• Demekin. The Japanese form, typically with a deeper, more ryukin-like body and a hint of shoulder hump.
• Butterfly tail. Selected so the tail spreads wide and flat, read from above rather than the side. A different viewing tradition on the same fish.
• Black moor. The solid-black telescope. The British show standard treats it as a separate type; the care is much the same.
• Panda. Black and white, and frequently unstable — many panda telescopes do not stay panda, for the reasons the moor page sets out.
• Dragon eye. A trade name for the protruding eye itself rather than a distinct variety.
• Calico, chocolate and blue. Colour lines on the standard body.

And the neighbouring breeds are not telescopes. A celestial eye has eyes that rotate upward and no dorsal fin; a bubble eye has fluid-filled sacs beneath upward-pointing eyes. Both are generally considered more fragile than a telescope, not less.

How the eyes develop

A telescope is not born a telescope, which surprises people who buy a small one. Fry hatch with ordinary eyes, and the protrusion begins within the first two or three months and keeps developing, though no published source gives a finer timetable for telescopes.

So a young telescope can look like a plain fantail for months, and how far the eyes will project is a property of the line rather than of anything you do — the argument in breeding goldfish about buying from someone who grades applies here as much as anywhere.

A slightly uneven pair is common. A large difference, or one eye that changes after having been settled, is a different matter and belongs on popeye and bulging eyes.

What a telescope can actually see

Worth understanding, because every practical recommendation on this page follows from it.

It is not blind. A telescope registers light, shadow and movement, learns to come to a hand at the glass, and recognises the person who feeds it.

It is generally described as focusing badly. Published work links the enlarged eye to raised pressure inside it and to a thinner retina, though acuity has not been measured; small objects directly in front of the fish are said to be the hardest thing for it to resolve — which is unfortunately where food is.

It compensates with two other senses. The lateral line detects water movement and obstacles, and smell finds food. Goldfish anatomy and biology covers both properly, and it is the page that explains why a fish with poor sight is not a fish in difficulty.

The practical consequence is that a telescope needs time at feeding and consistency in where food appears, and it needs a tank it cannot injure itself in. Both are easy; neither is optional.

Designing the tank around the eyes

The whole of telescope husbandry, in one section.

• Nothing sharp. Run a hand over every ornament; if it catches skin it will catch an eye. Aquarium decorations covers the test.
• Nothing with a narrow gap a fish could push into.
• Sand or bare glass, not coarse gravel — substrate for goldfish covers grain size.
• A sponge over the filter intake, always. A protruding eye against an uncovered intake slot is a recognised risk in the breed, and the filter buying guide treats the pre-filter sponge as part of the purchase rather than an accessory.
• Gentle flow, so the fish is not pushed into anything.
• Low, open decor rather than tall structures to navigate around.
• A feeding spot, used every time.

Choosing one

1. The eyes first. Both clear, undamaged, roughly matched.
2. Then swimming. Level, unhurried, fins open.
3. Then eating. Watch a feed if you can, and see whether the fish finds food or gives up.
4. Read the shop’s whole system, as choosing and bringing home a goldfish sets out.
5. Quarantine for at least four weeks — quarantining a new goldfish.

A fish with one damaged eye is not a fish to reject on welfare grounds. It will live well. Buy it knowingly rather than by accident.

Where you will find one. Widely available, and sold young, which matters because the eyes do not reach their adult protrusion for months. A juvenile telescope looks much less dramatic than the adult it becomes, so buy for health and body shape and let the eyes arrive in their own time. Coloured varieties beyond the standard orange and black tend to need a specialist.

Personality and behaviour

Telescopes are calm, unhurried fish that spend the day nosing along the bottom. Their vision is poor: a telescope reacts to a shadow or a hand at the glass, but its ability to judge distance and pick out a pellet in front of it is limited, so it relies on smell and on the lateral line, the sensory system that detects water movement.

In a tank of telescopes and black moors, everyone finds food at the same pace. Add a fast single-tail or even an enthusiastic ryukin and the telescope will be last to every pellet. They are entirely peaceful; the risk runs the other way, so check combinations with the compatibility checker.

Aquarium requirements

Plan on 100 litres (26 US gallons) for the first telescope and 40 to 50 litres for each additional fish, with a long footprint rather than a tall one. Everything a telescope can bump into should be smooth: rounded stones, smooth wood, silk plants or soft live plants such as anubias, and no resin ornaments with holes and ledges or gaps the head could wedge into. The decorations guide covers what works.

Filter intakes need a sponge pre-filter so that eyes and fins cannot be drawn against the slots. Keep the outflow gentle, since a strong current pushes a round fish around the tank; the filtration guide explains how to soften a powerful filter. Many guides give 18 to 24 °C (64 to 75 °F) and some breed societies 15 to 20 °C; keep the water stable, with 25 to 40 percent changed weekly.

Substrate should be sand or bare glass: small gravel can be swallowed, and sharp gravel is exactly what a poorly sighted fish should not be rooting through.

Feeding

The base of the diet is a good sinking pellet made for fancy goldfish. Drop it in the same spot at every meal; within a few days the fish learns where food arrives. Sinking food also avoids the air-gulping at the surface that so often precedes a floating episode in round-bodied fish.

Feed small amounts two or three times a day, only what is eaten within a couple of minutes. Because a telescope finds food slowly, watch each meal: if a faster tankmate is emptying the feeding spot, spread the food or feed at two points. Blanched peas, zucchini and spinach, gel food and frozen daphnia or brine shrimp bring variety, and gel food is especially useful because it stays where it lands.

Common health considerations

The eyes are the vulnerable point. A knock against a hard edge can scratch the cornea or damage the eye itself. Cloudiness in one eye is usually the result of a scrape or of poor water quality and typically clears in clean water; cloudiness in both, swelling behind the eye or a rapidly growing bulge deserves more attention, and the cloudy eyes guide walks through the possibilities.

Buoyancy problems are the other recurring issue, as in all round-bodied fancies. A fish that floats, tilts or sinks after a meal has often gulped air or overeaten, and sinking food with a day’s fast sometimes sets it right, though vets find other causes too. Fins tear on sharp decor and in strong current; clean water heals most damage, but fix the cause.

What goes wrong, in order

Almost all of it traces to the eyes or to being slow.

What you see	Usually	Where to look
One cloudy eye	A scrape on decor, gravel or a net	Cloudy eyes
Both eyes cloudy	Water quality first, though other causes exist	Cloudy eyes
A bulging or swollen eye	Infection or fluid, not the breed	Popeye
A damaged or lost eye	An intake, an ornament, a net	First aid
Floating or tipping after meals	Often diet, though other causes exist	Floating upside down
Thin, with no obvious cause	Beaten to every meal	Chasing and bullying

One eye versus both is a useful distinction here. One is an event that happened; both is a condition the fish has, which usually means the water. That split is the same one the popeye page makes, and it saves a great deal of guessing.

Living with a one-eyed fish

Common enough to be worth saying plainly, and more cheerful than people expect.

A telescope that loses an eye usually copes. Telescopes are generally described as seeing poorly, and the lateral line and smell do much of the work, so the loss may remove less than it would from a fish that hunts visually; it still needs time to adjust.

What it needs afterwards is what it needed before, applied more carefully: smooth surroundings, a consistent feeding spot, unhurried company, and time at meals.

Watch the socket for a fortnight while it heals, keep the water clean, and resist the urge to treat — first aid for an injured goldfish covers why clean water beats anything applied, and why the cause needs finding before a second eye goes the same way.

Is a telescope right for you?

It suits you if you like a slow, characterful fish, you are willing to furnish a tank around its limitations, you will feed deliberately in one place, and you can keep it with other unhurried fancies.

It does not suit you if the tank holds single-tails, if it is full of rock and ornament you are attached to, or if you want a fish that looks after itself. A telescope is not difficult; it is unforgiving of a tank furnished without it in mind.

And it is a breed worth thinking through. Protruding eyes are a selected trait with a real cost, and the argument in goldfish welfare about how far selection should go is one a telescope keeper should have read — the moderate forms are a good deal easier to defend than the extreme ones. Expect roughly 7 to 10 years, and up to about 15 in an exceptionally well-kept fish.

History and origin

Goldfish with protruding eyes, called dragon eyes in China, a name that survives in English as Dragon Eye, were kept there by the late sixteenth century, the earliest possible reference being from about 1590. The trait is a recessive mutation, traced in recent work to a single gene, and was fixed by selection. From China the fish spread to Japan, where it became the demekin, roughly “protruding-eye goldfish”, and Japanese breeders produced lines with matched, symmetrical eyes and the deeper ryukin-type build.

The telescope reached Europe and North America in the late nineteenth and early twentieth centuries with the wider goldfish trade. It has since become one of the parent breeds of the fancy goldfish family: the black moor is its black form, some authors treat the celestial eye as a mutation of the telescope, though genetic work suggests the two arose separately, and the panda and butterfly lines are recent developments.