By Jessie M Sanders, DVM, CertAqV
A fish pond can be a grand addition to any home. Koi are one of the most commonly kept pet fish for large, outdoor ponds. Originating from grass carp, generations of breeding for color and shape have yielded the beautiful nishikigoi, or brocaded carp, also commonly called koi. These specific mutations have been bred for centuries into the magnificent fish you see today.
There are many varieties that one can purchase or adopt for a koi pond. Before purchasing fish, make sure you are buying from a reputable breeder or store. Visit the store pond and make sure the fish are bright and active with no signs of disease prior to purchase.
The Gosanke group is made up of the Kohaku, Sanke, and Showa varieties of koi. These highly prized koi are the winners of koi shows across the globe. The Kohaku are prized for their deep red bands. The Sanke are similar to the Kohaku, but have minimal black marks, called sumi, spread along their backs. Showa have the same external pattern as Sanke, but they have black skin under their markings, unlike the Kohaku and Sanke, which have white skin under their markings.
These three variety of koi have very specific color standards that distinguish them from the plainer koi. Koi show judges are highly trained to be able to characterize the markings correctly. The Gosanke tend to be the more valuable and expensive type of koi.
Doitsu koi are a variety bred in Germany. “Doitsu” is a derivative of the word “German” in Japanese. These koi are distinguished by having minimal or no scales. They may just have a zipper of scales along their lateral line or dorsal fin, a few speckled here and there, or no scales at all.
These fish can be very confusing to a new koi enthusiast. Without the overlying scales to protect each other, Doitsu koi may lose a scale occasionally and have large blemishes in their skin. There is nothing sickly about these fish, they are just bred to a different standard than other koi. In a pond with good water, these holes will heal up quickly with no damage to the fish.
Doitsu are also more prone to injury when they are flashing, or itching themselves, with any parasite infection. Some Doitsu koi are good show fish, specifically the Asagi, but they do not win any top prizes.
Koi with long fins are known as Butterfly koi. They can be any koi variety with elongated fins throughout their entire body. However, with these delicate fins come frequent tears and scarring if your pond has too many obstacles for them to maneuver. With each tear, the fin will scar over and shrink down, which can cause fin deformities if they are constantly injured. Perfect fins on a Butterfly are very hard to achieve. Despite their beauty, this fish never wins shows.
Gin Rin fish can be any subtype of koi, including Gosanke and Doitsu, but they have sparkly scales. Some fish may have only one or two metallic scales, or they may be metallic throughout their body. If a fish loses a metallic scale, there is no guarantee that the one that grows back will keep the metallic coloration.
Although not show fish, these plain brown koi are known for their outgoing personalities and monstrous appetites. Usually the first to arrive for feeding time, they will learn to hand-feed willingly. This variety of koi is beloved by pond owners.
Be they scaled or Doitsu, Chagoi are very friendly and can grow quite large with their hungry appetites.
Since these ponds are commonly outdoors, they are subject to seasonal temperature variations. For this reason, it is very hard to keep any tropical variety fish in an outdoor pond. If you are looking to increase your pond diversity, here are the varieties you should stick to.
These hardy koi cousins do very well in outdoor ponds. They will eat the same diet as the koi and can grow to very large sizes if kept properly. They can also cross breed with koi, so if you keep them in the same pond and a spawn occurs, you may have some hybrids the following spring. There are many varieties of goldfish in a wide range of color patterns.
These sleek fish can provide a good contrast to koi and goldfish, but keep their carnivorous diet in mind. Catfish can do well on koi food, but if they get hungry and a sickly koi drifts by, they may decide to take a bite! They have been known to attack fish much larger than themselves. Catfish have a unique body; they are covered in taste buds rather than scales. This feature makes them more sensitive to poor water quality in your pond.
Although not a true elasmobranch, like other sharks and rays, these fish have large black fins, allowing them to zip through ponds with amazing ease. They are not aggressive towards any other pond fish. They are algae eaters but will snack on koi food if it is readily available.
No matter what kind of fish you decide on for your pond, keep in mind that filtration must be adequate for the size of the pond and the bioload, or amount of fish. Keep up with regular maintenance in order to keep your water chemistry parameters at good levels. Water quality is the best thing any owner can do to optimize excellent fish health.