Goldfish (Carassius auratus) are freshwater fish and are often the first fish that people keep as pets. Most aquarists have had a goldfish at one time in their lives. They belong to the family Cyprinidae.
Goldfish are originally from China where they were selectively bred to obtain the fancy varieties commonly seen now. My favorite goldfish has always been the comet goldfish. You can often obtain plain comet goldfish by purchasing feeder goldfish. They look similar to the fish in the above photo. The fancy varieties of goldfish have longer fins and fatter bodies, such as that shown in the photo on the left. These fancy varieties wouldn't survive in the wild because they swim too slowly. However, they do fine in aquariums where they don't have to worry about predators as they would in the wild. I've personally never found them to be as aesthetically pleasing as plain comet goldfish, but many people prefer the fancy varieties.
Slim varieties of goldfish can reach a size of 12 inches or 30 cm in length. The fatter-bodied varieties are usually smaller than this. They can accept a wide range of water temperatures from about 50-86 degrees Fahrenheit (10-30 degrees Celsius). Because of this, you will often see goldfish kept in fishbowls rather than in an aquarium. While it is true that they can survive in a wide range of water temperatures, they still need adequate filtration and aeration in their environment.
Now, I'll have to admit that when I was a small child I had two goldfish in a fishbowl, but unfortunately they didn't live very long. This is too bad because goldfish can live for many years in the proper environment.
If you want your goldfish to be happy then they must be kept in an aquarium just like any other fish. They will be the happiest and the healthiest there and they will live much longer than if they are kept in a fishbowl. You must provide adequate space for them, and have a good filtration system.
Goldfish readily eat dried food, such as dried tropical flakes, and they will also eat insects, tubifex worms, bloodworms, small crustaceans, such as brine shrimp, and plant matter.
They can be kept in a community tank, although occasionally they will harass other smaller fish. Also, remember that some goldfish can grow quite large and they'll need plenty of swimming room. In addition, goldfish are coldwater fish and typically prefer colder water than most tropical fish do.
The first thing you need to know is how to tell a male goldfish from a female. There are no body color differences. Females are typically wider and fatter than males. Also, males have small bumps on their gill plates, called tubercles. These turn white when the male is ready to breed.
Conditioning the Pair
To get them into proper breeding condition, feed them lots of live or frozen meaty foods (e.g., brine shrimp, bloodworms). Place them in a breeding tank that contains a lot of plants and do partial water changes daily. It is beneficial to put a spawning mop in the tank. They are most likely to spawn when the water temperature is between 65-75 degrees Fahrenheit or 18-24 degrees Celsius.
Spawning and Care of Fry
Goldfish are egg scatterers. Remove the pair after spawning is complete so that they don't eat the eggs or the fry once they hatch.
The eggs will turn yellow in about one day. This is normal. Fungus is sometimes a problem with fish eggs and so if you see any that begin to grow fungus remove them so that it doesn't spread to the rest of the eggs. The fry will hatch in about a week. At higher water temperatures the eggs will hatch more quickly.
When the fry first hatch they will still have a yolk sac attached, which they will absorb over the next two or three days. Once they are free-swimming they will need to be fed. You can feed them commercial liquid fry food, small pieces of hard-boiled egg yolk (which the commercial fry foods often contain), and newly hatched brine shrimp. If you find hatching brine shrimp to be somewhat cumbersome you can now buy instant baby brine shrimp by Ocean Nutrition that is ready to feed to your fry.