China, there are historical documents which date back to 1770 which indicate the ryukin first appearing in Japan.
The hump which starts immediately after the head.
Ryukin are quite robust and healthy. Their extreme body shape means that they could be prone to issues concerning their swim bladders but this can be minimised with good breeding, a good diet and relatively shallow water.
Ryukin can grow in to quite large fish which can reach 8 - 10 inches (20 - 25cm) so they will need a suitably sized aquarium to house them.
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.
Ryukin are generally quite healthy and robust. They are not strong swimmers and can't compete with more normal fish, their long finnage does not do very well in very cold conditions so they are not really suited to life in an outdoor pond and should only be kept in an indoor aquaria.
As of yet 2014 there are no set British show standards for the ryukin goldfish below are the American show standards for the ryukin..
Fish will be bright, alert active and well balanced.
Metallic varieties: Red, red/white, pure white, greenish, blue, calico and chocolate.
Nacreous varieties: Solid red, bi coloured, tri coloured and Calico.