People have bred goldfish in captivity for hundreds of years, starting in China and Japan. Goldfish reproduction is well-understood, and goldfish life stages and care needs are well-known. If you decide to breed goldfish, you should understand the needs and characteristics of each stage of development.
Goldfish eggs develop best at 68 degrees Fahrenheit to 70 degrees Fahrenheit. They typically hatch in two to three days. You should remove any unfertilized eggs, which appear cloudy, since they encourage fungus growth. It is normal for only 80 percent or so of the eggs to develop. Fertilized eggs will appear clear, then slowly hatch into fish. Once the baby fish or fry hatch, they will live off their yolk sack for the first 24 hours. After this, they require food.
Some pet shops sell liquid foods for fish fry. You can also make your own, using a mixture of hard-boiled eggs and oatmeal ground into a paste or very tiny bits. After a few weeks, they will grow large enough to take more common foods, like baby brine shrimp or fish flakes ground up into a powder. You should feed them about three times a day, feeding only what they can eat in 20 minutes (extra will pollute the water).
When goldfish hit the 1-month mark, they can eat more or less what adult goldfish eat. They need food of a smaller size, including small fish pellets and ground fish flakes. But they will eat most of the foods an adult goldfish would, including live foods for treats. At 4 months, goldfish look like miniature adults. At this point you can treat them the same way you would an adult goldfish, feeding regular goldfish food like flakes.
Goldfish reach maturity and can breed at around 3 to 5 inches, or 10 to 36 months. There are many varieties of goldfish, and details of later development vary considerably. Additionally, most goldfish don't get their adult coloration until their second year. Many common goldfish don't loose their brownish-silver coloration and turn gold until this time, and some never do. Certain fancy goldfish develop more quickly, a side effect of years of selective breeding.
- Goldfish Lanterns image by Toronto Canada from Fotolia.com