ALL ABOUT KOI

:: Koi History
:: Koi Growth
:: Koi Age
:: Koi Sexing
:: Can Koi overeat?

Koi History

Today Koi are bred in every country and considered to be the most popular fresh-water ornamental pond fish and are often referred to as being "living jewels" or "swimming flowers".
Koi are a variety of the common carp, Cyprinus carpio. Carp fossils have been discovered in South China dating back about 20 million years. Some varieties are known for their hardiness, which records claim can live for long periods of time if simply wrapped in wet moss continuously kept damp.
Some authorities believe Koi originated in Persia and spread throughout the ancient world.
Koi, or nishikigoi - Japanese for "brocaded" carp - were first described in writing from a Chinese book written during the Western Chin Dynasty, 265-316 A.D. At that time they were described as white, red, black and blue.
What happened to Koi from the 2nd to the 17th century is still being investigated, but many suspect Koi were gradually spread around the orient, and possibly even via trade caravans to or from the middle east.
Koi breeding in Japan is recorded from the 17th century in the rice-growing region of the Niigata Prefecture. They were originally bred as protein food supplements.

Koi Growth

Some Koi can get to be a meter long which is 100 centimeters, 3.28 feet or 39.37 inches. However, modern Koi average closer to 80 centimeters (31.5 inches), which is still a long way from the 1/16th inch of the newly hatched Koi.
Using the Ludwig von Bertalanffy growth equations (1938) it can be shown that generally Koi reach about 50% of their final adult length at 24 months, 95% at 10 years, and 99% at 14 years.
Obviously their size depends on the environmental conditions such as pond size, oxygen concentration, water temperatures, water quality, amount and type of food, and length of the growing season. Vitamins, exercise, and lack of stress may also play an important role.
In the mid 1980's in Lake Biwa in Japan they netted a 6.5 foot Cyprinus carpio, but it died in a public aquarium in Kyushu. There are other examples of carp reaching enormous sizes in large bodies of water. The mahseer, a member of the carp family Cyprinidae, genus Barbus, typically reaches 6.5 feet and a weight of 200 pounds. It is found in Southeastern Asia. Although that is a big fish, it is not as big as the wels, also called WALLER (species Silurus glanis), a large, voracious catfish of the family Siluridae, native to large rivers and lakes from central Europe to western Asia. One of the largest catfishes, as well as one of the largest of European freshwater fishes, the wels attains a length of about 4.5 m (15 feet) and a weight of 300 kg (660 pounds).
Back to our favorite Koi. It appears that depending on their age and under optimum conditions Koi can grow over 2 centimeters (almost an inch) per month or faster, remember there are 2.54 cm in an inch. Check out the growth rates in the following graphs.

Koi Age

Many of us wonder, "how old is our favorite Koi"? One way to guess at the answer is to measure how long they are, and then check the Koi Growth Charts.
However, most Koi have scales; thin, overlapping plates of bone that continue to grow throughout life. As they grow they do not increase in number, but rather increase in size. The growth of the scales is proportional to the Koi's growth, and annual marks are formed on the scales at the same time every year, along the outer edges.
So if you look at a Koi scale, it turns out that just like trees in cross-section, they have annular rings. If your Koi has lost a scale, look at it closely, even under a microscope. Then count the number of annular rings, and your Koi is at least that old, but it maybe even older. This is more accurate for younger Koi, i.e., less than 5 years old.
However, if a Koi looses a scale, and then grows it back, the new scale will not have any of the older rings. Also females may not add growth rings when they are reproducing, or grow some more after reproducing, causing 1 growth ring to look like 2.
A more accurate way to judge a Koi's age is to examine the cross-section of a fin spine, which also has annular rings. The second anal fin spine is often used. This can be done without doing permanent damage, since the fin will grow back.

Koi Sexing

It is difficult to tell the sex on younger Koi, it gets easier as they get older.

Females tend to have rounder bodies and rounder pectoral fins and their fins tend to be somewhat smaller.

Males are sleeker, with more pointed pectoral fins, and their fins tend to be larger.

Others claim the colors of males are more brilliant.

Older males have a sand paper like raspiness on the gill plates, and some claim you can also feel a roughness if you lick your tongue across the front of the pectoral fin. If you try this let us know!

The easiest way is when there is a particularly aggressive male chasing the females, with the proverbial nose up the butt, you look for other males chasing the same now identified females.

Can Koi overeat?

Koi make ammonia from the food they eat. Koi are sometimes referred to as ammonia machines. The reason for this is because of the quantity of food that they eat. This ammonia is made in several different ways:

Koi respiration introduces ammonia through the gills

Koi digestion generates ammonia through:

Urine

Feces

Un-eaten food decomposes into several chemicals including ammonia.

Sediment on the pond bottom, consisting of feces, plant material from within the pond as well as wind-blown leaves, and other dead organisms, also generates ammonia.
We can calculate the ammonia generated by the food by making a few assumptions:
1. We feed just the proper amount of food each and every day, which establishes a "Steady State" condition producing the same amount of ammonia each and every day. Once we know the weight of food we feed each day the calculation becomes easy.
2. Koi eat about 1% to 2% of their body weight in food each and every day, but the calculation should be based on the actual weight of food we feed daily.
3. The protein content of Koi premium pond food is typically 36%, but sometimes is as high as 40%.
4. The nitrogen content of protein is typically 16% (the Kjeldahl Analytical Method is based on this).
5. So multiplying the weight of the food by the % protein, and then by the % of Nitrogen in the protein, we know the weight of atomic Nitrogen going into the water.
6. If we know the volume and thus the weight of the water, we can then calculate the ppm of nitrogen.
7. A few calculations based on these assumptions for a typical Koi pond, show that this results in the production of 1.6 ppm of atomic nitrogen every day.
a. This creates 1.9 ppm of ammonia
i. (4.3 ppm for 2% food - 40% protein)
b. 1.9 ppm of ammonia creates up to 5.2 ppm of nitrite
i. (11.6 ppm for 2% food - 40% protein)

So each day we generate 1.9 ppm of ammonia, and up to 5.2 ppm of nitrite. When we measure the amount of ammonia and nitrite actually present, we know the difference is the amount "digested" by the bacteria daily.
If there are no bacteria to digest the ammonia and nitrite, and there are no water changes, then the ammonia concentration will increase by 1.9 ppm per day; the nitrite by up to 5.2 ppm per day.
Under these conditions the Koi will soon die from the toxicity of ammonia and nitrite. A couple of weeks in water over 20 ppm of ammonia or nitrites and we will have mostly dead Koi, the ones still alive will have Columnaris and Aeromonas infections, such as hole in the side disease, fin rot, tail rot, secondary fungal infections, etc..