Keeping Koi - Pros and Cons

Do your homework first

By Phil Allen

Keeping Koi - Pros and Cons

The common carp is a hardy fish, and koi retain that durability. They can be kept in anything from small containers to large outdoor ponds (see water garden). Although Koi can grow to 90 cm (3 ft) if you have one with a good bloodline[citation needed], the traditional indoor aquarium is less desirable than a round plastic tub. Koi are cold water fish, so it's advisable to have a meter or more of depth in areas of the world that become warm during the summer. In areas that get harsh winters, it is a good idea to have a pond that is a minimum of 1.5 meters (4 1/2 feet) deep so that it won't freeze solid. It is also a good idea to keep a space open with a bubbler and a horse trough heater.

Koi's bright colors put them at a severe disadvantage against predators; a Kohaku looks like a visual dinner bell against the dark green of a pond. Herons, kingfishers, raccoons, cats, foxes, and badgers are all capable of emptying a pond of its fish. A well-designed outdoor pond will have areas too deep for herons to stand in, overhangs high enough above the water that mammals can't reach in, and shade trees overhead to block the view of aerial passersby. It may prove necessary to string nets or wires above the surface.

The pond should include a pump and filtration system to keep the water clear.

Koi are bottom-feeders, so koi food is not only nutritionally balanced, but designed to float so as to encourage them to come to the surface. When they are eating, you can also check for parasites and ulcers. Koi will recognize the person feeding them and gather around at dinnertime. They can even be trained to take the food from one's hand. In the winter their digestive system slows nearly to a halt, and they eat very little, perhaps no more than nibbles of algae from the bottom, and their appetite won't come back until the water warms up in the spring. If kept properly, koi can live about 30-35 years. Some have been reportedly known to live up to 200 years.

Breeding Koi

Like most fish, Koi reproduce through spawning in which a female lays a vast number of eggs and one or more males fertilize them. Nurturing the resulting offspring (referred to as fry) is a tricky and tedious job, usually done only by professionals. Although a Koi breeder may carefully select the parents they wish based on their desired characteristics, the resulting fry will nonetheless exhibit a wide range of color and quality. Unlike a purebred dog or cat, even the finest champion-grade koi will produce literally thousands of unacceptable, unrecognizable, or even genetically defective offspring in a single spawning. These (and hundreds of marginal offspring) are culled at various stages based on the breeder's expert eye and closely guarded techniques known to a rare few outside japan. Culled fry are usually destroyed (perhaps fed to other fish) and older culls are often sold as lower-grade "pond-quality" koi within their first year (also called "Tosai")at 3"-6" in size. The semi-randomized result of the Koi's reproductive process is both a blessing and a curse. While it requires diligent oversight to narrow down the favorable result that the breeder wanted all-along, it also made possible the gradual transformation of wild river carp into the exquisite art form that we see in modern nishikigoi.

In the wild

Koi have been accidentally or deliberately released into the wild in every continent except Antarctica. They greatly increase the turbidity of the water because they are constantly stirring up the substrate. This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking even by livestock. In some countries, koi have caused so much damage to waterways that vast amounts of money and effort have been spent trying to eradicate them, largely unsuccessfully. Because of the danger to the environment Koi possession is illegal in the State of Maine.