It's a question that some people ask, but goldfish do not give live birth so they technically don't become pregnant in the same manner as to which we've become accustomed.
Goldfish are oviparous, meaning they produce eggs that will eventually mature and hatch after the eggs are expelled from the body like monotremes (mammals that lay eggs instead of giving birth) and most reptiles, fishes and birds.
Determining The Gender
You can usually discover the gender of your goldfish by observation and comparison. Fuller bodies, plumper bellies, shorter and rounder pectoral fins, along with comparisons to other fish will aid you in determining the gender of your goldfish. Keep in mind however, that a plump fish doesn't necessarily mean she is preparing to lay eggs.
Candling Your Fish
Sometimes it is difficult to determine your goldfish's gender. A common practice is to remove your fish to a separate jar for observation using a process called 'candling.' This is achieved by shining a flashlight through the jar and the fish while you then examine the fish. If you have a female goldfish, the added light may aid you in better seeing the eggs she is carrying. One caution: do not use a military grade flashlight!
Egg Laying Signs
The mature female goldfish begins egg production in late winter and early spring. If you're observing your female goldfish and you notice her refusing food after previously having a healthy appetite, this may be a sign of an impending egg laying. You'll also notice less activity as the weight of the eggs tend to slow down your goldfish. Brighter than normal coloring and visual signs of nesting behavior suggests egg production time is getting close! And what are those visual signs? Your fish will stay close to all vegetation and even hide within some vegetation or other places of shelter within the tank.
The Signs From The Male
The male goldfish will also experience physical and behavior changes as their breeding time approaches. You'll notice white bumps on their gills and pectoral fins (the fins on their sides.) The males will also bump the females sides and bellies and chase the females around the tank in an attempt to encourage the female to release the eggs.
The Oviparous Process
When temperatures rise (around 68 degrees Fahrenheit), is when goldfish breeding takes place. The unique thing about goldfish is when they become fatter and swell with eggs they will then release hundreds or even thousands of her un-fertilized white eggs into the water, near vegetation where the eggs will stick. They do this without the presence of a male. But how then are the eggs fertilized? Simple. After the eggs are released, the male releases sperm which then connects with the eggs. Fertilized eggs are golden brown and transparent. A male fish is needed for fertilization or the eggs won't hatch. This is called spawning and usually takes place in the wee hours of the morning.
Time to Hatch
Goldfish eggs will hatch in two to seven days depending upon water temperatures. Warmer temps mean a faster hatching while colder is a slower hatching. Goldfish young-ins are called fry. The fry carry with them a yolk sac that will supply food to them for a few days. When the yolk sacs are depleted it's time to feed your fry some brine shrimp or daphnia. If your intent is to breed your fry, you must remove all of the adult fish to another tank or they will eat the fry whenever they can! Feed your young goldfish three times a day but don't overfeed. Fry eat live or specialized liquid food and powdered flakes.
About the Author
Tom Matteo has been a freelance writer since 1992. He specializes in hardware and software reviews for computers and gaming systems, and occasionally writes about such topics as animal behavior and care. Tom resides in Bethlehem, PA with his wife Tina and his beloved cockapoo, Angel.