Shubunkin Goldfish Breeding Guide

How to breed the shubunkin goldfish (Carassius auratus): sexing, spring temperature trigger, scattered adhesive eggs, hatching and selecting for calico colour.

Overview

The shubunkin is a single-tailed, hardy variety of the goldfish, Carassius auratus, and follows standard goldfish reproduction. It is an egg-scattering, oviparous spawner whose sticky eggs attach to plants or submerged objects; females release several batches of eggs across the spawning season.

Sexing

Sexes cannot be told apart reliably outside the breeding period. As the season nears, males develop breeding tubercles, white pinhead-sized spots on the gill covers, head and sometimes the pectoral fins, while gravid females become rounder and deeper-bodied with eggs.

Conditioning

Adequate space and good nutrition are required for goldfish to reach spawning condition, and cool water during the winter months is necessary for proper development of the ova. As a robust, single-tailed variety often kept in ponds, shubunkins respond well to the natural seasonal temperature cycle that conditions breeders.

Breeding Setup

Set up the spawning medium before chasing begins, using dense fine-leaved plants such as Cabomba or Elodea or an artificial spawning mop for the adhesive eggs to attach to. The eggs cannot be moved after being laid, so the medium must already be in place.

Spawning Behavior & Trigger

Spawning usually follows a significant rise in temperature in spring. At around 20-23 degrees C (68-73 degrees F) males chase gravid females from dawn into early afternoon, bumping and nudging them so they release eggs, which scatter over the plants or mop and are fertilised by the pursuing males.

Egg & Fry Care

Remove the parents once spawning is over, because goldfish eat their own adhesive eggs and the eggs cannot be relocated. Eggs hatch in roughly 48 to 72 hours (about four days), and fry are free-swimming around 24 hours later, when feeding begins with newly hatched brine shrimp or a fine fry food. Fry take on their final shape within a week or so but remain metallic brown like wild ancestors, often needing about a year to develop adult coloration.

Common Challenges

The shubunkin is bred for its nacreous calico pattern of blue, red, orange, black and white, so fry are graded and culled to select the desired colours and pattern; only a portion of each spawn shows good calico. Being a single-tailed variety with an unmodified body, shubunkins spawn naturally without the difficulties of heavily modified fancy goldfish.