Sexing Goldfish Getting Started Breeding Hatching Culling

Goldfish Breeding Websites:

Bristol Aquarists - A breeding guide from the Bristol Aquarists website.

AGA Artical Database - This is a section on the American Goldfish Association website with articles detailing how to breed and raise goldfish.

Vermillon Goldfish Club Diary - This is the website of a goldfish club in Singapore...this article is a diary on raising Ranchu fry.

Peter Ponzio - A detailed eZine article, with a lot of information on culling as well.

AquaArticles - A breeding guide by Jennifer Wilkinson.

Olympic Koi Club - Though a Koi club, this article has information on breeding goldfish as well.

Goldfish Breeding Forums:

   Kokos Breeding Forum - The breeding subforum on Koko's webaite.

   Goldfish Keepers Breeding Forum - The Breeding subforum of the Goldfish Keepers website.

   Raffles Gold Breeding Forum - You will need to create an account to view topics.


  Spawning Chase - Video showing a pretty good example of a Goldfish Spawning Chase.

  Aquatic Central Breeding Tutorial - A video breeding tutorial from a fish sotre in San Francisco.

  Hand Spawning - Video of a Chinese Goldfish Farmer demonstrating hand spawing (Not in English).



Some things you need to know before breeding goldfish:

Goldfish kept in overstocked tanks will probably not reach sexual maturity. Overstocking will result in dwarfed specimens with stunted growth. To reach sexual maturity, your goldfish will need an ample supply of water volume...15 gallons per fish or more. While it is possible they could still reach sexual maturity in smaller water volume, the more space you give them, the more likely they will fully develop. In a pond environment (lots of water) goldfish will often breed by themselves. The effort described here is mostly necessary only with aquarium goldfish.

For the sake of simplicity, I will be using the fahrenheit scale for temperature, and the imperial scales for length (inches) and volume (gallons). You can find converters online here:

Temperature Converters (Fahrenheit to Celsius)
Eggheads - MetricConversions.Org - TPG.COM

Length Converters (Centimerters to Inches): - MetricConversions.Org - CalculateMe.Com

Volume Converters (Gallons to Liters):
CalculateMe.Com - GallonsToLiters.Com - Webmax

You need to be comfortable with the idea of culling...your goldfish will probably produce hundreds of offspring. You will not likely be able to keep all the fry as pets unless you have a lot of space (Either a pond or lots of large tubs). You will want to keep only those fry with the best characteristics of their breed, which is only going to end up being a very small percentage of the total clutch. Most of the fry will either end up Euthanized and flushed, or fed to predator fish.

What follows is intended as a summary. If you are serious about breeding goldfish, I would suggest visiting one of the forums or breeding-specific sites in the sidebar.


Males will develop white spots on their face and gill covers when they are in breeding condition

Before you can even consider breeding goldfish, you first have to determine their sex, which can be more difficult than it sounds. Because prior to sexual maturity, they are almost impossible to tell apart.

Goldfish are sexually mature at one year, but are in their prime at three years. They need to reach about 3 inches as well...if the goldfish has lived in an overstocked tank it's growth may be stunted, which could affect it's ability to breed. Breeding goldfish need optimum water conditions, which means 15 gallons per fish at a minimum.

The male is the easier of the two to sex. When he is in breeding condition, he will develop breeding tubercles...these look like white raised spots about the size of a pin head, similar in appearance to ick, and they will cover his face, gill covers, and pectoral fins. His pectoral fins will also be thicker than those of a female. This is usually true even of younger goldfish.

Females will have wider abdomens than males of the same breed, and will usually be uneven when viewed from the top profile. The female's cloaca will also be slightly portruding (in males it will be flat or concave). When they are ready to breed, their body will swell, becoming larger and more rounded as they develop eggs inside.


To breed goldfish you will need the following:

 Two sexually mature goldfish of the opposite sex. Ideally, they should be separated prior to breeding.

 Two fully cycled (and heater equipped) at least 29 gallons and the other at least 20 gallons (where the fry will eventually live).

Mix the water between to two to ensure it is the same chemistry.

 Do not use a power filter in the fry tank...use an undergravel filter or (better) a sponge filter. You will eventually be lowering the water level in the fry tank to six inches or less, so plan accordingly.

 The breeding tank will need spawing material to catch the eggs in. Pet stores sell Spawning Mops (you can make a homemade one here), or you can use live plants. Hornwort will work well. Pet stores will also sell breeding grass, which is a fake plant that looks like a small patch of grass.


These fertile eggs are well developed, as you can see the embyos inside

Goldfish only mate once a year. Breeding behavior in goldfish is triggered by temperature changes. Water temperature needs to be raised in 2F degree increments per day from a starting point of 50F degrees. The optimal temperature is 68F to 70F, but breeding behavior can be triggered within a range of 50F to 78F.

Breeding behavior consists of a "Spawning Chase"...the male will swim behind and below the female for several hours, occasionally bumping into her ventral area (stomach). This behavior alone is not evidence of the goldfish's sex...males will also chase each other in the absence of females. The male will get gradually more aggressive, as it is this behavior that stimulates the females to release her eggs.

The female will release several batches of eggs, pausing between each batch. The male will then immediately spray "milt" (goldfish sperm) on them, fertilizing them. The female will instinctively lay the eggs in dense plant material or anything that looks like it (such as a spawning mop). The eggs are adhesive and will stick to the first surface they are layed on. Adult females will lay between several hundred and a thousand eggs or more.

The Eggs can be handled gently without rupturing or damaging them (though it is ideal not to touch them if you can avoid it), and should be removed immediately or the parents removed from the breeding tank. The parents will eat the young after they hatch, and might even eat the eggs before they hatch. The eggs should be placed in the 20 gallon tank. Make sure there is not more than six inches of water in this tank, as too much water pressure will crush the eggs.


Goldfish fry at 1 day old

The optimal temperature for incubation of the eggs is 68F to 70F degrees. The clearer the egg, the more likely it is fertile. Fertile eggs will also develop black dots inside them...these are the fry (baby fish) embryos.

Fungus will attack infertile eggs, but may eventually spread to the fertile eggs. So infertile eggs should be removed as they appear. There are anti-fungal medications sold in pet stores specifically designed for eggs and fry, as normal medications may be too harsh.

Goldfish eggs develop quickly...they will hatch within 48 to 72 hours. It is normal for only 70% or 80% (or even less) of the eggs to hatch.

Once they hatch, the fry will sink to the bottom. This is normal. They will feed off of their yolk sac for the first 24 hours, and do not need to be fed during that time. Once they have consumed this yolk, they will begin swimming around.

  The first few days

1 day old fry are extremely small...between 1/8th and 1/16th of an inch long. They are about the same dimensions as human eyelashes. They will begin as a "wild" type gray color, no matter what breed or what color their parents looked like. Breed specifc characteristics do not appear until later in their development. Within 48 hours they will start to develop pectoral fins.

At this age they cannot eat normal food...they will be eating stuff that is almost microscopic in size. Like adult goldfish, they are not picky...they will eat anything they can fit into their mouths, be it plant or animal. Normally they would eat stuff living in the pond (algea, microscopic organisms, ect..), but it is best to prepare food for them to help them grow well. They can be fed Hard boiled eggs or oatmeal ground into a fine paste or powder. Pet stores also sell liquid food specifically for fry. Uneaten food needs to be removed so as not to foul the tank.

Goldfish fry (probably Ranchus) at 1 month...notice how they are beginning to take on the body shapes of their parents

  At A few weeks

At a few weeks, they can begin eating more normal food. An ideal food is live baby brine shrimp, which you can buy at pet stores or grow yourself using kits sold at pet stores as well. There are instructions on the internet for how to make your own hatchery, and the brine shrimp eggs can be bought online and at many pet stores that sell fish. They can probably eat ground up flake food at this point. They should be fed three times a day, for 20 minutes at a time.

  At A Month

At a month old, they can be fed normal goldfish food. Very small pellets, flake food, or live food. Amounts should be as much as they can consume in a 20 minute period.

  At 4 months

They are basically miniature adult fish at this point, and can be fed the same way you would feed adults.


Culling is the process of separating the fry with the most desirable characteristics. Culled fish are typically used as feeders for predator fish, or euthanized. The specifics are largely a matter of opinion and experience, and will be a bit different for each breed. Fancy varieties especially do not breed true with a lot of the fry. Only a fraction of the original spawn population will probably be acceptable.

What follows is just a general summary. You will want to visit one of the breeding-specific sites or forums for details.

Ten to Fourteen days after hatching, for fancy varieties you will want to do the first culling. Cull all of the fry without double tails. You will also want to cull any of the fry that have obvious deformities.

The next culling should be done at 1 month, selecting for favorable body shapes, as they will have little or no color at this time. You will probably end up culling about 20% to 40% of the fry at this point.

At 2 months, another culling can be done selecting for body shape again, but also color. You will probably cull about half of these fry or more.

At 3 months, another culling is done selecting for breed specific characteristics (such as wen), as well as things like fin shape. After the 3rd culling, it is normal for only 5% to 10% of the original spawn to remain.

At 6 months, the final culling is done, selecting the specimens that conform most closely to the breed standards (or whatever standard you are looking for). By this time it is normal for only 1% of the original spawn population to remain.

From 1000 eggs, you may have only 5 to 20 fish remaining after the final cull. This is using Chinese methods...American methods tend to be less harsh when it comes to culling, which results in a proliferation of less desirable specimens.

Member of