Is it a boy or a girl? How to determine the sex of your
koi? By Blue Ridge Fish Hatchery
1.) The Shape
The sex of a young Koi does not
affect its body shape until it begins to reach sexual maturity, which is
usually at around three years of age. Most females at this age will start
to carry eggs and will tend to be more rounded and "blimp"
shaped. Males are more streamlined and torpedo shaped. Males lack the
swollen abdomen of females. Generally speaking, females will grow to a
larger size than males. Take a look at the pictures for an example
of the two.
2.) The Feel
Generally by two years of age, male
koi will start to feel rough to the touch, especially during the spring
season as temperatures are rising. If you rub your fingers on the gill
plates and along the side of the body, it feels like sandpaper. Females
will be slick and smooth to the touch.
3.) The Vent
The male vent will be
more con-caved in appearance where-as the female vent will be convex
and slightly protruding with a slight pink appearance
4.) The Behavior
During the spring spawning season
sexually mature males will chase the females, nudging them with their
nose to encourage her to release her eggs.