Breeding Goldfish
How to breed Goldfish (Carassius auratus): sexing by breeding tubercles, a temperature-driven spring spawn, adhesive eggs on plants, and fry care.
Overview
Goldfish (Carassius auratus) is an egg-scattering, plant-spawning species of intermediate breeding difficulty. Goldfish can only grow to sexual maturity with enough water and the right nutrition. Some heavily modified fancy varieties can no longer breed naturally because of their altered shape and may require hand-stripping.
Sexing
During the breeding season males develop breeding tubercles on the head and pectoral fins and have a streamlined body with a concave genital papilla. Mature females are plump-bellied with a protruding genital papilla.
Conditioning the Breeders
Good nutrition and adequate space are required for fish to reach spawning condition, with females filling visibly with eggs.
Breeding Setup
- Spawning temperature around 23-28 °C, within the coolwater species range
- Dense plants such as Cabomba or Elodea, or a spawning mop, to hold the adhesive eggs
- Ample volume, since spawns can be very large
- Gentle filtration that will not draw in eggs or fry
Spawning Behavior & Trigger
Breeding typically follows environmental changes, particularly in spring. Males chase gravid females and prompt them to release eggs by bumping and nudging. The adhesive eggs attach to aquatic vegetation; fecundity is substantial, with around 1,000 eggs per female recorded in a controlled study at a one-female-to-three-male ratio.
Egg & Fry Care
Eggs hatch within 32-72 hours depending on temperature (about 32-40 hours at 23-28 °C). Shortly after hatching the fry begin to assume their final shape but remain a metallic brown like their wild ancestors; a year may pass before mature goldfish colour develops. Fry grow quickly and can be fed cultured live zooplankton, with a mixed live-and-prepared diet performing best in study conditions.
Common Challenges
Adults readily eat eggs and fry, so spawning media and separation matter. Some fancy varieties cannot breed naturally and require assisted hand-stripping, and the delayed colour change means juveniles look like wild-type fish for months.