Nearly everyone has had a Carassium auratus at one time or another, although you may have called it a goldfish. It may have come in a tiny bowl, been won as a prize at a fair or given as a party favor at a birthday. And most likely it didn't survive more than a few weeks or was released into the local pond.

Goldfish are one of the most hardy fish in the aquarium and in the wild. They have been known to live as long as 25 years and can grow as long as 2 feet. And while you may have gotten yours for free, or paid a dollar or two, collectors will pay as much as $1,000 and more for a prized specimen.

The original greenish-brown goldfish was native to East Asia. First bred and prized by the Chinese as an aquarium fish, its popularity brought it to aquariums around the world. Fish escaped from ponds and released from aquariums have made the fish common in the wild. Since they can withstand a wide range of temperatures, and unlike most tropical fish, can survive in cool water, wild populations of goldfish live in the Hudson River in New York and in the streams and ponds of the Midwest.

More Than 125 Varieties of Goldfish

Breeders have developed more than 125 different varieties, from the common pet shop "comet," to the wide-bodied and bulging eyed dappled orange, to white veiltails and celestials. Some of these fish can look more deformed than attractive, but to the breeders and enthusiasts they are highly prized.

While goldfish are hardy, even the most common varieties require good care, beginning with a tank bigger than a goldfish bowl. Given enough space and attention they will grow large, from 6 to 14 inches depending upon the variety. They will also live long, on average from 7 to 10 years.

Housing

For two goldfish, you'll need a tank of at least 20 gallons. This may seem large when the fish are young, but they will quickly grow. The water must be de-chlorinated. The best way to do this is with a chemical de-chlorinator available at any pet shop. A good filtration system that provides both mechanical and biological filtration is necessary, and an airstone to help circulate the water is also recommended.

If the temperature of the room stays between 65 and 75 degrees, a heater is not needed. These fish can take cool water as long as the water temperature doesn't change drastically over a short period of time. Gravel on the bottom of the tank isn't necessary but if you do use it, make certain you siphon up the fish waste and excess food that drifts to the bottom.

Food

Perhaps the one major concern with keeping goldfish is that they produce a great deal of waste, which can quickly fill the tank with ammonia. Goldfish will eat constantly if you allow them, but their stomachs are literally only as large as their eyes, so try to imagine an eye or two full of food for them, given over the course of the day rather than all at once. Flake goldfish food is usually sufficient for the basic diet. This can and should be supplemented with some boiled spinach or lettuce, or with some live food such as brine shrimp or tubifex worms. Again, feed only small amounts at a time.

Because of their production of waste, keep a close eye on water conditions. If the tank begins to appear cloudy, make a large water change over and above the quarter of a tank change that you make weekly. Feed them less. If you feed them with floating goldfish pellets, make certain to soak the pellets first so that they swell up before you feed them to the fish. If you don't, the fish eat the dried food and it swells up in their stomachs causing problems with their air bladders. The result is known as "flip-over" disease in which the goldfish begin to swim and float sideways or upside down.

Goldfish will quickly become used to your feeding them and come to the edge of the tank when you enter the room. They are flashy swimmers and fun to watch so long as you take them out of the bowl they came in.