Hi members,
please sex this koi for me. This will be my Dainichi female for 2021 spawning if it turns out to be female. Its name is May. I hope the offspring has its body shape.
I'm not that good at telling by the vent. So others may have better insights there.
Judging by the body shape, I look at the way the thickness of the body narrows from the chest to the tail. Males tend to have a steadily narrowing slant that is nearly a straight line when viewed from above. Females with eggs (if they have not laid them) will have a curve that can be seen from the side and even from above. So the narrowing as you go from the chest to the tail on a female will be very slow and gradual at first. Then at about 2/3 of the way down the length of the koi, around the vent area, the koi will narrow very rapidly. This one looks rather straight, with the body shape of a male, though a robustly built one. For mature koi, this body shape observation makes it easy to tell male from female on maybe 80% of koi, but for about 20%, the traits are less pronounced and can be mistaken, in really stout males and in some females that don't get all that eggy.