Comet Goldfish (Carassius auratus) Breeding Guide

How to breed the Comet, a single-tail Carassius auratus variety: spring temperature trigger, adhesive eggs, 48-72h hatch and fry care.

Overview

The Comet is a single-tailed variety of the goldfish, Carassius auratus, a member of the family Cyprinidae native to China. It was developed in the United States from the common goldfish by Hugo Mulertt in the 1880s and is distinguished by a long, single, deeply forked tail fin and a slimmer body than the common goldfish. Like other goldfish, it is an egg-scatterer that breeds readily, particularly in ponds and large tanks.

Sexing

Mature males develop breeding tubercles — small white, pimple-like bumps — on the gill covers and along the leading rays of the pectoral fins during the breeding season. These gradually disappear after spawning. Females are identified by a plumper, fuller body as they fill with eggs. Tubercles can occasionally appear on females, so they are not an absolute guide to sex.

Conditioning

Goldfish reach spawning condition with adequate space and good nutrition. A varied diet brings females into roe and prepares males to display tubercles. Comets are active fish best conditioned in spacious cool-water systems such as ponds or very large tanks.

Spawning Behavior & Trigger

Breeding usually follows a significant temperature change, often in spring. A simulated seasonal warming after a cool period is the typical trigger. During spawning, males chase the gravid female and prompt her to release eggs by bumping and nudging her, after which the eggs are fertilised in open water.

Egg & Fry Care

Goldfish eggs are adhesive and attach to dense aquatic vegetation such as Cabomba or Elodea, or to a spawning mop. Eggs hatch within 48 to 72 hours. Within a week the fry begin to assume their final shape, though a year may pass before they develop mature goldfish colour; until then they are a metallic brown like their wild ancestors. Fry grow quickly, an adaptation to the high risk of being eaten by adult goldfish, so separating eggs or fry from adults improves survival.

Common Challenges

Single-tail varieties such as the Comet are selectively bred for body and finnage, so rigorous fry selection (culling) is used to maintain type. Adults readily eat their own eggs and fry, making physical separation important.