Breeding goldfish is not that hard, but requires patience, since the process can take several months. We assume that you have kept goldfish in proper tanks for few years and are familiar with their different types and care needs.
These tips are intended to provide the readers with general advice and more important to prevent common mistakes. Further and detail information is encouraged.
Tips for breeding goldfish for the first time:
1. Ask your breeder to provide you with mature specimens ranging from four to six years old. Although two years old goldfish are sexually mature, it should not be your first choice, especially when trying to breed them for the first time. Select two males per female.
2. There are two methods for sexing goldfish: One is to look for salt type spots on the opercular region and on the first ray of the pectoral fins as an indication of a male. The other method is to determine sex by the shape and appearance of the anal opening. My advice? let your breeder help you choose your “boys” and “girls”
3. A bare 40 gallons Tank with mops is recommended.
4. Start feeding them three times a day with live foods: brine shrimp, chopped worms as well as fresh vegetables.
5. The water temperature should be kept initially in the mid thirties to forty degree range. After two months start raising the aquarium temperature gradually to fifty to sixty degrees for about four and six weeks. Finally, raise the temperature to sixty-five to seventy degrees in preparation for spawning.
6. After this long period of time your fish should be ready to spawn. Some signs of courtship include, males chasing females and rubbing against the mops and each other, it usually begins in the morning and continues during four to six hours. At one point the females will lay their eggs and the males will fertilize them by releasing their sperm.
7. Remove the eggs/spawning mops at this time. Place them in separate tanks with water at the same temperature as the breeding tank.
8. The eggs will take around seventy-two hours to hatch and the fry will be less than one quarter of an inch long. Their bellies will have yolk sacs. This will nourish them for a few days, do not feed them at this time. After that you will need to feed them finely sieved daphnia or newly hatched brine shrimp. Remove uneaten food and use a sponge filter with low turbulence. At two weeks of age you can begin culling unwanted fish by using a magnifying glass.
9. Fertile eggs will be pale amber to pale yellow in color. Infertile eggs will be opaque in color and eventually become fuzzy as fungus develops, remove fungused eggs. To control fungus add methylene blue or malachite green.
Source: Breeding Goldfish by Rick Graham. First published in “Tank Topics”, Greater Akron Aquarium Society, Aug/Sept 2001