Ranchu Goldfish Breeding Guide

How to breed the Ranchu goldfish (Carassius auratus var. Ranchu): spring spawning trigger, egg scattering on plants, ~4-day hatch and selecting the dorsal-less back and wen.

Overview

The Ranchu is a selectively bred variety of the goldfish, Carassius auratus, distinguished by the absence of a dorsal fin, a deeply curved back and a prominent head wen. It spawns with the same egg-scattering biology as other goldfish; the difficulty lies in producing offspring that show the smooth dorsal-less profile and well-formed wen prized in this variety.

Sexing

Mature goldfish are sexed most reliably in the breeding season, when males develop small white breeding tubercles (stars) on the gill covers and leading pectoral-fin rays. Gravid females become noticeably rounder and deeper-bodied. Tubercles are typically present from spring through autumn.

Conditioning

A breeding programme normally starts in early spring with the water warmed to about 17 degrees C (63 degrees F), with fish well reconditioned after the cooler winter. Breeders commonly spawn one female with two or three males, and add plenty of fine-leaved spawning medium such as hornwort or a spawning mop.

Spawning Behavior & Trigger

Spawning is triggered by a significant temperature rise in spring as the water approaches about 20 degrees C (68 degrees F). Males chase the gravid female and prompt her to release eggs by bumping and nudging. The adhesive eggs scatter and stick to plants such as Cabomba, Elodea or a spawning mop.

Egg & Fry Care

Because goldfish eat their own eggs, parents must be removed as soon as spawning is over (the eggs are adhesive and cannot easily be moved). The eggs hatch in about four days and the fry become free-swimming roughly 24 hours later, when feeding begins. Fry are an undistinguished metallic brown and may take a year before developing mature goldfish coloration.

Common Challenges

Producing show-quality Ranchu requires heavy culling: only fry developing the smooth dorsal-less back, correct curvature and an even wen are kept. Some highly selectively bred goldfish can no longer breed naturally due to their altered shape, so selecting healthy, vigorous breeders that still spawn reliably is part of maintaining the line.