The Goldfish Carassius auratus which come from China was one of the very first fish to be kept
ornamentally. It dates back to 265 AD when the Chinese were the first people to keep fish as pets.
The first line bred coloured varieties were around soon after in 500 AD and they had become popular
pets by 1200 AD. The first twin-tailed fancy varieties appeared in 1600. And by 1700 the Japanese
had developed some fancy varieties and keeping them had become very popular and they had reached Britain
and by 1800 they reached America.
The wild type was originally bronze coloured but by breeding fish without black pigment the red layer underneath was revealed, and by further selective breeding so that the fish had no red pigment revealed white fish.
Goldfish can be very long lived and there are reliable records of some fish reaching forty years although half that is more usual.
Don't use a Goldfish bowl, instead use a proper tank because the larger the volume of water the more stable it will be and this will be much better for the fish so will the extra space. The minimum size of tank should be 24 x 12 x 12 inches which holds 10 Imp gall and would be suitable for two fancy goldfish up to 4 inches in size with adequate filtration.
Under gravel filters are not really suitable because Goldfish produce lots of waste and if the temperature of the water is below 60°F this waste will not break down quickly enough and there is every likelihood that pathogenic bacteria will multiply in the deteriorating water quality and the weakened fish will get a bacterial infection most probably in the form of fin rot. There are a number of solutions to this problem
Regular partial water changes are essential this should be done on a weekly basis and about 20% of the water should be changed. Make sure that you treat the new water with de-chlorinator and that it is the same temp as the water in the tank. When changing the water it is a good idea to clean the filters at the same time and use the old tank water to clean the filter sponge in and never tap water. Do not mix fancy Goldfish with ordinary Goldfish because there is a great risk of bullying and the fancy Goldfish may not get enough food because they are generally not able to compete in the same way.
Ordinary goldfish grow very big and with good care they will grow fast. Their growth is not restricted to their tank size. Small specimens can be kept in an aquarium until they grow. These fish really belong in a properly made pond which is at least 4ft deep and filtered.
Temp - 38°F to 86°F a massive range, but all changes must be made slowly.
Ammonia/Nitrite - no trace.
Nitrate - < 20ppm.
pH - 7.5
GH - avoid extremes.
KH - 5 to 12.
Goldfish are omnivores with a slight preference for vegetable matter. The main thing when it comes to feeding them is to ensure they have a balanced diet for healthy growth and resistance to disease. Their mouths are slightly down-turned and it isn't natural for them to feed at the surface and it can lead to swim bladder and other digestive problems if they are forced to, so ideally all dried food should be pre soaked prior to feeding so that it will sink. Suitable food
If you go away on holiday rather than risk someone with no experience feeding them it is better if the fish are left without food.
For a healthy Goldfish to go two weeks with no food will do no harm at all. Being cold blooded their food requirements are far less than an equivalent sized mammal but the risk of over feeding poses a very real threat to their lives.
Goldfish tend to be seasonal breeders with daylight hours and temperature and the availability of food all acting as spawning triggers. They are egg scatterers and they will eat their own eggs if given a chance.