How to tell male or female koi carp?


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gomer answered
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The differences between male and female koi

The differences between the sexes become more apparent as they age,
particularly so in the spawning season. Male koi are slender, compact
and torpedo-like in appearance, with very trim lines and smooth body
contours. They also show behaviour that is particular to male koi and is
particularly noticeable when all male koi are segregated into a single
tank. Male koi tend to dart around energetically, with sharp turns of
speed, showing real 'attitude' and a skittish character. They are less
trusting than the opposite sex and this shy temperament is all the more
apparent at feeding time when they will take considerably longer than
females to feed at the surface.
The key distinguishing physical feature that male koi possess
develop in late spring as they come into breeding condition. Often
mistaken for whitespot, breeding tubercles appear on the head, flanks
and tail of mature male broodfish. To the touch, these tubercles make
the typically slippery koi feel 'as rough as sand paper' giving them
better purchase for when they drive and push against gravid females in
an attempt to expel their eggs. In darker koi, white tubercles will be
clearly visible but on paler or metallic koi, tubercles may only be
evident to the touch.
Females on the other hand, do not develop tubercles nor will they
retain the sleek lines of a male as the breeding season approaches. Eggs
that develop in the ovaries will swell, leading to an increase in
volume to the abdomen. In addition, female koi tend to behave in a less
timid manner to a tank full of males, feeding voraciously as soon as the
food hits the water. Whether these characteristics are as well defined
and identifiable in a pond of mixed koi is debatable, but males are
still less likely to be the first to feed of the surface.

The Hands-on Method.

The sure method of sexing koi is to roll up your sleeves and exert
some timely pressure in the right place. As long as the water
temperature is above 15 degrees C, males should be producing milt, which
can be expressed by applying finger and thumb pressure either side of
the vent. A ripe and mature female when turned upside down (having been
sedated) will show a swollen abdomen and a pink and fleshy protruding

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