Before goldifsh breeding can occur, your first have to sex your goldfish. Unfortunately, they only show their gender during mating season, so it can take two - three full seasons prior to actually breeding any goldfish. The males with develop 'tubercules' that can look like little white pimples that show up on the gills, and sometimes the head. Female gold fish are easily recognizable by their body shape, their abdomens will swell with mature eggs.

Typically a goldfish over the age of 1 year, or longer than 8cm, can be accurately sexed. However, prime breeding occurs during the third year. Once an accurate sex can be determined, it is best to seperate them prior to breeding. Sexing occurs during the summer months, followed by a fall and winter of seperation. Once Spring comes around and the breeding goldfish are well conditioned they can be included in a breeding tank. Slightly more males should be included than females ( 3 : 2 / 2 : 1 ). Spawning can occur naturally, or by forcing increase in the water temperature. Breeding typically occurs in the high 60°F, but it is the increase in the water that causes the breeding and not the actual temperature itself.

Let the chase begin.
If all the conditions are right, within a few days of being put together, the male has a ritual "spawning chase". The male goldfish will follow the female and push against her abdomen, for several hours. The female will lay her eggs in batches, the first being the most fertile. In total a female goldfish can lay up to several thousand eggs and more. The male fish will immediately fertilize the eggs by spraying 'milt' on them. 

Goldfish will scatter the sticky eggs all around the aquarium in no particular order, so it is best to have a tank that is well stocked with a wide variety of aquarium plants. Because the eggs are sticky, they will adhere to the first thing they come into contact with. Goldfish eggs should be about 1.5mm in diameter and amber colored at first. If the eggs turn white, they are infertile and should be removed from the breeding tank. It is important to note that the adult goldfish will eat the eggs, so it is recommended to remove the adult fish immediately following breeding. 

The goldfish eggs will hatch at about 70° F, about five days after being laid. Once hatched the embryo will need 3 - 4 days to absorb the yolk sac that it incubated in. Once the fry have digested the yolk they will require food fed to them 20 minutes at a time. After the 20 minute feeding time has expired always remove any remaining food from the tank. The fry can have a commercial product, or an oatmeal paste, or even a boiled egg yolk fed through a stocking. Be carefult not to overfeed the fry, and the changes that will occur in the water can be fatal to the fry. 

Standard rules apply
Good Food + Good Water = Happy Goldfish.

Breeding Cheat Sheet 

• Sex the goldfish
• Seperate the goldifsh
• Bring the goldfish together with more males than females
• Raise the water temperature slightly to enduse breeding
• Remove adult fish from the breeding tank after eggs have been laid
• Raise the water temperature gradually to approx. 70° F
• Hatch Fry, do not feed for 3-4 days, or until yolk sac is gone
• Feed the newborn fry 

Breeding Goldfish can be fun and exciting, but can also be frustrating and time consuming. With a little practice, patience and care Goldfish Breeding might be the right hobby for you.