Fantail Goldfish (Carassius auratus) Breeding Guide

How to breed the Fantail, a twin-tailed fancy Carassius auratus: sexing by tubercles, spring trigger, adhesive eggs and fry selection.

Overview

The Fantail is a twin-tailed fancy variety of the goldfish, Carassius auratus (family Cyprinidae), originating in China and Japan. It has an egg-shaped body, a high dorsal fin and a long quadruple caudal fin whose double tail and anal fins are well divided into two matching halves. It is considered hardy and serves as the base for many fancy goldfish varieties, and is reported to be very easy to breed.

Sexing

As in all Carassius auratus, mature males develop breeding tubercles — small white pimple-like bumps — on the gill covers and leading pectoral-fin rays during the breeding season; these fade after spawning. Females become noticeably plumper as they fill with eggs. Because tubercles can occasionally occur on females, body shape and tubercles are best used together.

Conditioning

Fantails reach spawning condition with good space and nutrition. A varied diet conditions females into roe and prepares males. The ideal aquarium temperature for fantails is around 23 °C (73-74 °F); they are hardy but can be sensitive to prolonged cold-water exposure.

Spawning Behavior & Trigger

Breeding usually follows a significant temperature change, often in spring — a simulated seasonal warming after a cooler period. During spawning, males chase the gravid female and prompt her to release eggs by bumping and nudging her, with fertilisation occurring in open water.

Egg & Fry Care

Fantail eggs are adhesive and range from white to yellow-orange when healthy; a single female can produce a large number of eggs. Eggs attach to dense plants such as Cabomba or Elodea or to a spawning mop, and hatch within 48 to 72 hours. Fry begin assuming their final shape within a week but may take a year to develop mature colour, remaining metallic brown until then. Adults readily eat eggs and fry, so separation aids survival.

Common Challenges

Good-quality fancy specimens result from rigorous fry selection (culling) to maintain the twin-tail body type. Fantails may also develop telescope eyes from around six months of age, which influences sorting of offspring by type.