The first goldfish we'll talk about under "Types of Goldfish" is the "bad boy" of goldfish, the beautiful Ryukin!
The Ryukin is named for the Ryukyu Islands that lie between Taiwan and Japan. The Ryukin arrived in Japan sometime between 1770 and the early 1800s. It has become one of the most popular goldfish in Japan. Many English texts confusingly refer to the Ryukin as a Japanese Ribbontail, Fringetail, and Veiltail.
A good Japanese Ryukin has a pointed head and a very deep body with a pronounced hump behind the head. The dorsal fin is high and the tail is long, often twice as long as their body.
When it comes to types of goldfish, Ryukins are one of the most beautiful, however, they also are one of the most aggressive! Ryukins are the "bad boys" of the goldfish kingdom.
Many Goldfish Collectors have Ryukins with other types of goldfish for years with no problems, however, some Goldfish Collectors have had goldfish lose an eye from an aggressive Ryukin. Even after the goldfish have been together for a long time, for some reason the Ryukin becomes very aggressive and sucks the eye from another type of goldfish. I've never heard of a Ryukin becoming aggressive to another Ryukin except during spawning. Once you find this problem, remove the Ryukin at once, because it will strike again!
A tank full of Ryukins and no other types of goldfish get along just fine.
One other problem you must watch for with a Ryukin is "constipation". Because of the very deep body, Ryukins have more of a problem digesting their food than most other types of goldfish. Instead of the food passing through the Ryukin, sometimes the food stays in the intestinal tract, causing constipation which will cause the Ryukin to rise to the top of the tank belly up. Many Goldfish Collectors think that this action is a "swim bladder" problem, when it's just constipation.
It is very important to feed lots of spirulina and shelled green peas, these foods work as a laxative and will releive the problem, however, once a goldfish has this problem, you must be very careful not to overfeed. In fact, I would not feed anything one day a week to a goldfish that has this constipation problem.
Out of all the types of goldfish, Ryukins are one of the most beautiful. Yes, they can have some problems, however, with proper goldfish care and the right goldfish food they make an excellent goldfish companion.