It is important to ascertain the sex of each goldfish before breeding. But this would be effective only when they reach spawning condition. The goldfish pregnancy attempt should be started only after the first year. But until they reach 8 cm in length it is not easy to make them have sex.
When they reach three years it would be ideal for pregnant goldfish. Changes are made easily and clearly in male fish. The male develops white reproductive tubers. They appear on the gill operculum, on the anterior radius of the pectoral fins, and sometimes on the head the size of a pinhead. The pregnant gilthead gilthead’s stomach swells and fills up.
The change in water temperature triggers reproduction in all types of goldfish. The temperature of the water is changed to induce reproduction. The optimum temperature for breeding goldfish is 20ºC, although the temperature range can be between 10 and 26ºC for pregnant goldfish. Experts among breeders advise that fish be kept separate before breeding. Obviously, before sexing them, the possibility does not exist.
Breeders wait until the optimum temperature is reached or gradually increase the temperature by artificial means. Possibilities for increasing the success rate of reproduction lie in increasing the male to female ratio of goldfish. The ratio of one female to two males ensures the chances of successful reproduction. Each fish must have at least fifteen gallons of water. Overcrowding should be avoided as pregnant goldfish have a difficult time surviving in crowded conditions.
As the male swims behind the pregnant goldfish in a ritual spawning chase, he sends the message that they are ready for reproduction. For several hours, the male swims behind the pregnant gilthead sea bream and pushes it onto its stomach over and over again. A few days after the day the fish are gathered, the chase occurs if all the conditions for mating are perfect.