Goldfish spawning is a fairly regular occurrence, if the conditions in their tank or pond environment are just right. Of course you also need a male and a female to start the spawning process and it’s impossible to tell which is which until they mate for the first time. The male goldfish will have white flecks on both their pectoral region and gills, with their anal region being more internal, while the female anal region is outer, basically the opposite of mammal genitals.
The goldfish spawning act will start usually when there is an abrupt raise in temperature. This is because the eggs need temperatures over 70 degrees (F) to hatch and turn to fry. A tell tale sign of goldfish spawning is seeing one chase after the other non-stop. The female will do everything they can (including jumping) to get away from the male, as part of nature’s mate selection process. Most animals and mammals play “hard to get” in a way of finding the strongest mate, with the best genetics.
The male will continue chasing the female, actively ramming her hundreds of times in an attempt to coax her eggs out, so he can fertilize them. Most breeders will sex their goldfish and try to have 2 – 4 male goldfish for every female to improve the odds of healthy stock. In professional breeding environments, the males are sexed and kept separate from females until breeding is induced.
If the eggs are left in with the goldfish, the majority of them will be eaten. In cases where you want to maximize the number of fry (baby fish) from the goldfish spawning: Remove the eggs after the male has milted (fertilized) them and immediately rinse the eggs in water over 70°F, then place them into a separate aquarium that will be kept at the same temperature.