Common goldfish

Common goldfish are a type of goldfish with no other modifications from their ancestors other than their color. Most varieties of fancy goldfish were derived from this simple breed. Common goldfish come in a variety of colors including red, orange/gold, white, black and yellow or ‘lemon’ goldfish.

As pets

The Common goldfish has become a popular pet around the world. They are hardier than fancier fish, able to live in a variety of conditions ranging from aquariums to outdoor ponds, and can withstand change in water temperature and quality better. They also breed easier and truer to form than other fish. If well cared for, Common goldfish can live up to 20 or more years in captivity.


Common goldfish are social animals, and like to live in groups. They enjoy interacting with others of the same species and the overall breed is friendly. With proper care they can become quite tame, eating from hands and swimming frantically towards the owner.

When one goldfish is unexpectedly placed in a tank with other goldfish, it might try to rub up against the others to familiarize itself with them or to communicate that it is not a threat. The most common positions are side to side with heads facing forward, side to side with heads facing opposite directions, and perpendicular, where one goldfish swims above another and settles down over it. The fish will generally school together for a while. After a while this behavior will cease, and the fish will swim separately again. Who gets the most food usually has to do with the size of the goldfish, but sometimes a smaller one will be the more aggressive member of the school. There may be some infighting and nibbling at one another right after introduction, but usually only moody goldfish will do this. Goldfish are very competitive regarding food and do not share amongst themselves.

Small goldfish are semi-afraid of human contact and will do anything to avoid it. However, sexually mature fish are more brave. Large goldfish may eat from their owner’s hands without any prior experience. They will also nibble at anything new in their surroundings, except larger fish and predators. This is their way of tasting. Your fingers may get nibbled at, but keep in mind that the goldfish cannot harm you. After a few weeks’ time, goldfish will begin to follow their owners around the room. If you use a floating food, they will swim toward the top of the tank every time you come near.


It is a common practice to keep common goldfish in a small bowl but this allows waste in the water to build-up to toxic levels and does not provide enough oxygen. They should be kept in an aquarium of at least 10 gallons with a good filter. Actual recommendations range from this up to 100 gallons, but it is possible to enjoy goldfish even in smaller tanks.

Goldfish are curious fish that will quickly become bored without items or other fish to interact with. If placed in an aquarium or other small container without gravel, goldfish will settle to the bottom and only move when fed or frightened by sudden jolts. However, if placed in a tank with sufficient gravel, aquarium accessories or plants (real or fake) they will make themselves at home. Adding a few companion fish will also help, but make sure each fish has plenty of personal space.

When adding goldfish to a new tank it is important to place no more than two at a time. This allows helpful bacteria (which turns ammonia to nitrite and finally to nitrate) to grow. If introduced in too great a number before these bacteria grow, the goldfish will die from breathing in too much of their own untreated excrement. Even after the development of the biological filter, it is necessary to change about 30% of the water at least four times a month (or as necessary to prevent a build-up of harmful nitrate). The addition of live aquatic plants may reduce the number of times per month you will have to perform water changes, but only if the plants are growing (they will uptake nitrate as a source of nitrogen).

Common goldfish can be kept in outdoor ponds throughout the year with similar care but they may become sluggish and stop feeding in the winter. This does not mean they are sick, but rather that their metabolism has slowed.


Breeding commons is fairly easy. In breeding condition the males will develop small white spots on his gill covers and the female will become plump. The male will chase the female until she releases her eggs, then the male will release sperm and they will become fertilized. The eggs will then stick to any available surface. It is then best to remove the eggs to a separate aquarium as the adults are likely to eat them. When the eggs hatch into fry they will need to be fed very small food such as hatched brine shrimp or a ready made fry food. As they grow bigger they can eat finely crumbled fish food.


Common goldfish are usually hardy but can contract diseases. These can be caused by unclean water, overfeeding and overcrowding. In small aquariums, illnesses in common goldfish can quickly become fatal, meaning prompt treatment is important. Several symptoms can indicate sick fish: cuts on any of the fins, a change in scale or eye color, excretions from the nostrils, scales falling off or the fish frequently making trips to the surface. Many treatments can be bought to treat specific diseases, but the best treatment is prevention.

Goldfish as Feeder Fish

Common goldfish are often used as live prey for predatory fishes such as Oscars or Piranhas. They are also fed to larger crayfish, turtles, and frogs. Sold at only about one inch long, they are easily eaten by other animals. Often selling cheap, about 30 US cents a piece, they are often bought by the dozen. However, some people find it cruel to feed live goldfish to predators and consider it pointless since most predators will also eat dead prey.