Like the goldfish, Koi are a domesticated variety of the carp.
In fact, the word Koi comes from the Japanese word meaning "carp".
An interesting side note is that the same sound means love or affection in Japanese, so Koi have become symbols of love in Japan.
One time at which this can be seen is during the annual Boys Festival.
A hallmark of this festival is the koi streamers that are attached to the ridgebeams of the houses.
The first record of carp being bred for color was in the Sung Dynasty in China around the year 960.
Koi as we know them today were developed in the city of Ochiya in Japan during the 1820s.
By the start of the twentieth century the main color varieties had been set.
Although Koi and goldfish are both varieties of carp, goldfish were developed from the prussian carp while Koi are derived from the common carp.
Goldfish are actually the older breed.
They were brought to Japan from China in the 1600s and introduced to Europe in the seventeenth Century.
Goldfish are generally one solid color, either red, black or occasionally white.
Koi come in many more colors including, red, orange, yellow, black, white, silver or even blue or green.
However the colors of Koi are not only determined by heredity.
Other factors such as the environment that they live in and the diet they eat can also have an effect.
the color of Koi.
The basic nature of Koi is that they are cold water fish and this fact must never be forgotten.
Their pond should be at least three feet deep so that a good temperature gradient is maintained.
When the surface temperature of the water rises in the summer the Koi will go deep in search of the cooler water at the bottom of the pond.
If the pond is large enough, a tree or two planted beside it can provide cooler shady spots where the fish can loaf.
The drawback to this is that the trees can drop leaves and other material that are unsightly and can clog filters and spillways.
The biggest single factor that determines how many fish can live in a pond is the oxygen content of the water.
Temperature plays a role here as well because cold water can hold more dissolved oxygen than warm water does.
In a still pond oxygen is taken up by water at the surface, so when you factor in the need to have a pond at least three feet deep and you can see that a large volume of water is necessary.
When I started out with aquarium fish in the 1950s air pumps were quite expensive and many tanks were set up without any artificial aeration.
In those days the basic rule of thumb stated that you needed one gallon of water for every inch of fish.
Deep water aeration via pumps and airstones is a good way to infuse more oxygen into the water and also does away with the stagnant layer that often exists at the bottom of a pond.
The other way of increasing the oxygen in the water is by means of a waterfall.
The falling water is picturesque, sounds good, and the roiling of the water allows it to absorb more oxygen than it otherwise would.
One of the good points about Koi being cold water fish is that they can be left out in the winter.
In fact, there have been cases of carp being frozen in solid blocks of ice and simply picking up where they left off when it melted.
When the water temperature decreases, Koi sink into hibernation, becoming less and less active.
Unfortunately, they can still eat under these conditions.
Although they are able to eat, their digestive systems have shut down for the winter and the food can rot in their stomachs and sicken them.
For this reason Koi should not be fed when the temperature of the water has fallen below fifty degrees fahrenheit.
Outdoor ponds are prized for their scenic beauty and for the sounds of rippling water that sooth our senses, but they really need the flashing vibrant color of ornamental fish like the Koi to complete the vista.
A pond stocked with Koi brings peace to the mind and color to the eye.
What more could you ask for?