Bubble Eye Goldfish Breeding Guide

How to breed the bubble eye goldfish (Carassius auratus): sexing, spring temperature trigger, scattered adhesive eggs, hatching and culling of the fragile variety.

Overview

The bubble eye is a fancy variety of the goldfish, Carassius auratus, and reproduces by the same biology as all goldfish. It is an egg-scattering, oviparous spawner; the eggs are sticky and attach to water plants or submerged objects, and females release several batches of eggs across the season rather than a single clutch.

Sexing

Outside the breeding period the sexes look alike. As spawning approaches, males develop breeding tubercles, white pinhead-sized spots on the gill covers, head and sometimes the pectoral fins, while females in condition swell visibly with eggs.

Conditioning

Goldfish only reach sexual maturity with sufficient water volume and proper nutrition. Cool water over the winter months is needed for correct ova development, so a seasonal temperature cycle prepares breeders before the intended spawn.

Breeding Setup

Provide an adhesive-egg medium such as dense fine-leaved plants (Cabomba, Elodea) or a spawning mop, installed before spawning begins. Because the bubble eye carries fragile fluid-filled sacs beneath the eyes, the spawning container must be free of sharp or abrasive surfaces that could rupture them during the vigorous chase.

Spawning Behavior & Trigger

Spawning typically follows a marked rise in temperature in spring. At around 20-23 degrees C (68-73 degrees F) males chase gravid females from dawn to early afternoon, bumping and nudging them to release eggs that scatter onto the plants or mop and are then fertilised.

Egg & Fry Care

Remove the adults once spawning ends, as goldfish eat their own adhesive eggs, which cannot be relocated. Eggs hatch in about 48 to 72 hours (roughly four days), and fry become free-swimming around 24 hours later, when feeding starts with newly hatched brine shrimp or fine fry food. Fry assume their basic shape within a week or so but stay metallic brown like wild ancestors and may take a year to colour up.

Common Challenges

As a selectively bred variety, bubble eye fry must be graded and culled to retain the dorsal-less back and the paired eye sacs; only some of each spawn show the wanted form. Heavily modified fancy goldfish can lose the ability to spawn naturally due to altered body shape, and hand-stripping is sometimes used, though it can harm the fish if done incorrectly.