Sunday, April 09, 2006


Data Sheet

Scientific Name: Cyprinus Carpio
Other Names: Carp
Family: Cyprinidae
Origin: Japan
Adult Size: 90 cm (3 feet)
Social: Good.
Lifespan: 30 years
Tank Level: mid - bottom dweller

Minimum Tank Size: 40 gallons and up. Koi grows very fast, so you should be prepared to get a bigger tank
Breeding: Egglayer
Care: Easy - this is hardy fish
Ideal pH: 7.2 to 7.8
Temperature: 65°F-75°F, 20°C-25°C
Tank setup: - see below -

It is impossible to sex koi smaller than about 25cm(l0in) in length, because they are sexually immature.

Once the koi exceed this size, the testes (in males) and ovaries in females) begin to develop. The ovaries are much larger organs than the testes. Females are usually easier to spot, as the belly of a mature female koi is generally plump, whereas males remain streamlined and more 'torpedo' shaped.


Koi (Japanese: 鯉, koi) are ornamental domesticated varieties of the common carp Cyprinus carpio. They are very closely related to goldfish, and in fact the style of breeding and ornamentation has become very similar, probably through the efforts of Japanese breeders to emulate goldfish, but they are not goldfish.

In Japanese, the word koi simply means "carp" referring to the dull grey fish. Nishikigoi (錦鯉: "brocaded carp"), in Japanese are the ornamental carp. This article is about Nishikigoi, and uses the English word koi to refer to the colorful fish.


The common carp is a hardy fish. They can be kept in anything from small containers to large outdoor ponds. Koi can grow to 90 cm (3 ft). Some people thinks that the traditional indoor aquarium is less desirable than a round plastic tub for keeping koi.

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 koi 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.

Mixing with other fishes:

Koi can be mixed with other peaceful fish like goldfish. Avoid mixing them with smaller fish (that can fit into their mouth). Other good tank mates includes most bottom feeders.


Staple pellet foods are nutritionally balanced and should be the main food source for koi. However, their diets can be supplemented with a variety of treat options including fruits and vegetables. Since koi are omnivores that eat both meat and vegetable matter, these additions will be eagerly accepted.

With an abundant supply of fresh fruits and vegetables at reasonable prices, summer is the perfect time to offer koi something extra to eat. More importantly, summer is the main growing season for koi when they need to build their winter reserves. The extra nutrition and calories from fruits and vegetables encourage healthy growth and weight gain.

For a high-protein dietary supplement, consider freeze-dried foods such as krill and baby shrimp. Freeze-dried krill are very nutritious and full of natural vitamins, minerals, and are rich in carotenoid pigment for the added benefit of color enhancement.

The varied choices of supplementary treat options can make selection difficult, so experiment to discover new koi favorites. When feeding fruits or vegetables, cut them up into bite size pieces to make it easier for your koi to eat. Be sure to remove any uneaten food immediately since leftover fruits and vegetables can rot and compromise water quality.


Koi are considered immature until they are 3-4 years old. Color is not relevant to sex. Males stay long and lean. Females get a low bulge, often a flat tire-look to their lower rear half. Good spring protein will help get them ready for spawning, but don't feed protein foods before 60-65 water temperatures. Start with similar koi for the best results, showa, sanke, kohaku or Ogons of similar color. The percentage of attractive fish is low to start with; it will be much lower dissimilar fish are used. Females won’t go into a spawn naturally if there is not enough dominate males to complete the full egg stripping, nor would you want them to. Females that start releasing their eggs must finish or the eggs will rot inside the body and will poison or kill the fish if not removed. A ratio of 2-3 males the same size as the female is recommended.

Koi literature states they will spawn as the water passes over 70 degrees F, but my experience is that will go after the water has been raised this high and a cool spell brought it down once, and the second time they hit 70 they are triggered.

Koi eggs are individual tapioca-like spheres. They may cover roots and stick to the sides, but they are all independent. Those long strings of sticky eggs with black-grey centers that get wrapped around plants are frog eggs, not koi or gold fish.

Spawning material is a big plus both for inducing the spawning as well as helping to protect the eggs from being eaten from the adults. This is also needed if the eggs are being removed to a separate area to hatch and mature.


This is a very brief guide to some common koi diseases from Planet It is in no way a substitute for a good book on the subject or professional help. Unless specifically stated most of these problems can be treated using commercial remedies. Check with your local aquarium supplier if you don't know which to buy.

  • Sliminess of the skin. A greyish white film of excess mucus on the body. This is a reaction to protozoan parasites. Other symptoms of infection by these parasites are scratching and leaping followed by lethargy and failure to eat. Further risks are secondary bacterial and fungal infections of wounds caused by scratching. The parasites are particularly active in spring when koi are still recovering from winter.

  • White spot (Ich). White spots symptoms are scratching and swimming into the water inlet, failure to feed and lethargy. It is fatal if untreated. Fortunately commercial white spot remedies are widely available.

  • Anchor worm. The female worm buries into the skin and underlying tissue of koi to hold on. The damage caused can become a target for bacterial or fungal infection which can spread.

  • Fish lice - They have a sucker to hold on to the koi with needlelike mouthparts which they stick into the koi and inject a toxin. This causes intense irritation to the koi and they scratch and jump and can cause bacterial infection. If they infect the gills they cause severe damage and often death. Most antiparasite remedies will not kill fish lice, a strong chemical is needed which is not freely on sale. Ask a vet.

  • Gill maggots. Heavy infestations can cause severe damage, eroding the gill filaments and allowing secondary infections to develop.

  • Skin and gill flukes. These are the fish equivalent of fleas. They are two different types of flukes, but despite of their names both can be found on the body and the gills, feeding on mucus. They use hooks to hold onto the koi, this causes irritation and in a weak, sick or stressed koi can become a problem.

  • Saprolegnia fungus. One of the most common fungal infections of koi. The fungal spores will grow anywhere on the koi, including the gills, initially germinating on dead tissue. Their threadlike hyphae release digestive juices which break down the tissue so the fungus can absorb it, as the fungus grows these juices start breaking down living tissue. Fungus on the body appears as cotton wool like growths, it is hard to tell if a koi has it in the gills, but if it hangs at the surface gulping for air it is likely.

  • Carp pox. A virus that produces solid waxy lumps on koi. It will not kill koi and is generally harmless, but can look unsightly. It is most often present in small koi and in cold weather, clearing up disappearing when koi grow and in the spring when water temperatures rise.

  • Finrot and ulcers. A number of bacteria are associated with finrot, lesions and internal haemorrhaging, notably Aeromonas and Pseudomonas. Ulcers usually start at the site of an injury, the bacteria then infect it causing further damage, and fungal infection can also occur. Such holes result in osmoregulatory problems, leading to damaged kidneys and death if not treated. It is worth adding a weak salt solution to the pond as well as anti bacterial remedy, a concentration of 3gm per litre will help to restore the osmotic balance and reduce strain on the kidneys (make sure that the salt is fully dissolved before you add it to the pond). Finrot is easily noticeable, the fins and/or tail look chewed and are red at the edges. Secondary bacterial and fungal infections can develop.

  • Cotton wool disease. Another bacterial infection. The common name comes from the white tufts that develop around the mouth and spread to the body and fins, often leading to ulcers and a thin appearance. Flexibacter is the bacterium which causes this disease. Treatment with anti bacterial medicine is usually effective.

  • Dropsy. Raised scales (rather like a pine cone) and eyes standing out from the head. A sign of a number of conditions, may be congenital heart or kidney failure or an internal bacterial infection. Bacterial dropsy is infectious so treat with an anti bacterial remedy and if possible isolate affected koi.


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Yamabuki Ogon



Longfin Sanke


Gin Matsuba


Links to other awesome Koi sites:

1. a site where you can top grade koi. Warning, it is quite expensive for high quality koi.
2. another great site where top graded koi are sold.
3. another great site to buy top graded koi.

References Cited:

1. Koi - Wikipedia, the free encyclopaedia, Available, [Online],
2. Planet Koi : Koi Health, Available, [Online],
3. David M., How to Breed Koi, Available [Online],
4. Drs Foster & Smith, Supplementing a Nutritionally Balanced Diet, Available [Online],
5. How to Determine the Sex of Koi, Available [Online],

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