The goldfish (Carassius auratus auratus) is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish.
A relatively small member of the carp family (which also includes the koi carp and the crucian carp), the goldfish is a domesticated version of a less-colorful carp (Carassius auratus) native to east Asia. It was first domesticated in China more than a thousand years ago, and several distinct breeds have since been developed. Goldfish breeds vary greatly in size, body shape, fin configuration and coloration (various combinations of white, yellow, orange, red, brown, and black are known).
Selective breeding over centuries has produced several color variations, some of them far removed from the "golden" color of the originally domesticated fish. There are also different body shapes, fin and eye configurations. Some extreme versions of the goldfish live only in aquariums they are much less hardy than varieties closer to the "wild" original. With the many variations to this fish and it has a reputation of being easy to keep. As with any fish, they require optimum water conditions. The comet or comet-tailed goldfish is the most common variety of fancy goldfish in the United States. It is similar to the common goldfish, except slightly smaller and slimmer, and is mainly distinguished by its long deeply forked tail.
The food for this fish needs to be low in protein but high in carbo-hydrates, this is why it is often best to use specialist goldfish flakes or pellets to feed this fish. It is a voracious eater so the feeds should be kept down to what the fish can eat in two minutes. This should be done twice daily. Shelled peas, some blanched leaf vegetables and bloodworms should also be included in the diet.
It is often easier to breed these fish in ponds rather than aquariums but both are possible. The female will lay her sticky eggs on plants and they should hatch in 48-72 hours. The fry are very small when newly hatched but will grow in size rapidly. Their coloration will remain brown like their ancestors, but after 12 months the adult coloration should show through.
Goldfish are peaceful fish. Comets should not be combined with fancy goldfish, as the fancy goldfish will have trouble competing for food. If goldfish are combined with other freshwater tropical fish, it is best to limit this to catfish. Fancy Goldfish can also be combined with danios, ottos, white clouds, barbs, kuhli loaches and weather loaches.