Bubble Eye

Carassius auratus

Also known as: Bubble eye goldfish, Bubble-eye

Water Parameters

• Temperature: 18–24°C
• pH: 7–8.4
• Hardness (GH): 89–357 ppm (5–20 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

The most delicate and specialised of the widely-sold fancy goldfish, the bubble eye is a dorsal-less variety whose defining feature is a pair of large, fluid-filled sacs that hang beneath its upward-pointing eyes, wobbling as it swims. Those sacs are the whole appeal and the whole problem: they are fragile, prone to rupturing on sharp decor or filter intakes, only partially regrow if damaged, and can become infected, and they impair the fish's already poor vision. Everything about its care follows from protecting them: a bare or smooth-scaped tank, gentle filtration with guarded intakes, pristine warm stable water, a sinking diet it can find, and only the slowest, gentlest fancy tankmates. Reaching 10 to 15cm, it is a fascinating and endearing fish, but firmly one for the experienced fancy-goldfish keeper, not a first goldfish.

Tankmates

The most delicate of the common fancy goldfish, and the one with the strictest tank and tankmate rules. Its two large, fluid-filled eye sacs are fragile and rupture easily, so the tank must have absolutely no sharp decor, no exposed filter intake or strong current, and only slow, gentle tankmates: other bubble eyes, ranchu, black moors, or similarly slow, dorsal-less fancies. It must never be kept with single-tailed goldfish or faster fancies, which outcompete it and may even nip the sacs. Small fish and shrimp are unsuitable. It needs pristine, gently-filtered, warm, stable water and careful, sinking feeding, as its poor eyesight and slow pace make competition impossible.

Compatible with

• Ranchu
• Black Moor
• Pearlscale

Avoid keeping with

• Common Goldfish
• Comet Goldfish
• Shubunkin
• Fantail Goldfish
• Ryukin
• Oranda
• Cherry Shrimp
• Tropical Warm Water Species

Common Problems

• ruptured or infected eye sacs from sharp decor or strong flow
• very poor eyesight making feeding difficult
• swim bladder and buoyancy problems
• being outcompeted or bullied by faster tankmates

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20