A Scientifically Trained Long-time Garden Guide Looks at Koi

by rpacht
[This post is a response to the koi lecture notes from 3/21 post]

Common carp

Origins:  Koi are NOT mutant Indonesian river carp. Systematics: Koi are common carp (Cyprinus carpio) and belong to the “minnow family” family cyprinidae the largest family of fishes with over 2000 species with “primitive” body designs.  Most are small and believed to have originally evolved in Southeast Asia.  Carp are thought to have originated in Western Asia (Caucasus area).  Because of their fast growth and desirability as food fish, they were transported nearly everywhere in Eurasia quickly.

Carp have great value as aquaculture animals in that they grow very quickly, tolerate a wide range of conditions (temperature, salinity, oxygen concentration) and food sources.  Koi live 20-30 years on average and can attain about 50 % of maximum size in the first two years.

Cyprinus carpio vs carassius auratus:  Koi are not a unique species nor are they the same as “goldfish” (carassius auratus) they are not even in the same genus.  They share the same family so are cousins if you will.  Goldfish share lineage with “Crucian Carp” (Carassius carassius) that has been raised as a food fish in China for more than 2000 years.

Koi barbells

To those who are interested, there is a really easy way to differentiate carp from goldfish, which are selected for many of the same characteristics and can be easily confused.  Koi have barbells around the mouth goldfish do not.  These are not “feelers” but olfactory sensors.  These are to aid the fish in finding food on/in the bottom substrate as they are benthic feeders.

One look at a koi’s sub-terminal mouth would tell one intuitively that they do not feed standing on their tails in the water column as the speaker indicates.   The guides went on a garden visit over in Kirkland a couple of years ago and the owner of a spectacular koi pond and grotto tried to sell this same foolishness.  Either it was the same lady or there is some general misconception about this.  If the fish are standing on their tails to feed it is because they have been trained to do so.

Koi breeding is not an area of expertise for me but when asked to talk to the guide classes on several occasions I did some research on the history of it, which I will present here:

Koi

First record of carp in Japan about 200 AD kept by emperor.  They were brought from China.  A red mutant was discovered in Japan not Indonesia. In the 1820s in Niigata prefecture in rice irrigation ponds koi breeding and selection began. In 1800s in Europe scale mutations appeared, were selected by German monks and came to Japan in the 20th century. In the early 19th century color mutations that appeared were selected and bred and by the late 19th century color patterns were fixed to an extent.

In 1914 some of the most beautiful varieties were displayed at an exposition in Tokyo and some were presented to crown prince Hirohito. Until 20th century breeding was confined to the Niigati region.  Many color and scale variations have been developed mostly but not exclusively in Japan.  There are over 100 named varieties today.

The myth of a 200+ year old carp is exactly that, a myth.  Jesse brought to my attention a New York Times article about such a fish and I did a bit of research on the report.  There is no otolith data or even scale data to support such a claim.

In fairness I should note the handful of truths in Anon’s notes.  Females do grow larger than males, which is true of most fishes and biological organisms in general. A meter in length for a maximum is about right and about 10kg or so.
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The photos for this post came from the following websites:
•  U of Wisconsin Sea Grant Institute
•  Keep Koi
•  Fish Index