Selecting Koi by Gender

By Chai Taevanitcharoen
How to select tosai for Male or Female

No one can select tosai for male or female 100% of the time. Some tosai will show the characteristic of male or female 100% but some won’t, and some may be neutral fish. As your knowledge improves you will have better percentage of selecting male or female.

These are some guide lines when you are selecting male or female tosai. If you master all 4 you will be able to select male or female 99% of the time. Pictures are included below the notes to show what is being described.

Signs it’s a  MALE
1. Male develop color early (finished)

2. Beni and shiroji are rough, yellowish, or the body white but the head yellowish, especially the mouth, nose and cheek area. If the fish have all of the above, 90% male.
3. Pectoral fins are thicker. The primary and secondary bone look darker white color. If you have 20/20 eyes sight you may see little stars in the pectoral fins. If you are good at this technique, It would be almost 100% male selection.
4. Anal opening looks tear drop shapped, look long and sunk in. 90% possible male.

Signs it’s a FEMALE

1. 80% female won’t develop color early ( finish)
2. Beni and shiroji soft and shiny, the shiroji even from the tip of the mouth, cheek to the tail. If the fish have all of the above, 90% female.
3. The pectoral fins are thin and look translucent. The primary and secondary bones look lighter in color, and won’t have little star in the pectoral fins. If you’re good at this technique, you’ll get almost 100% female. Note: Nisai pectoral fins look different.
4. Anal round and rise up, it does not sink in. Possible female 99%

Extra notes:

1. I didn’t talk about rubbing, touching the pectoral fins for the roughness, lumpiness of  male fins because you need sensitive
   skin on your fingers and a lot of practice. I tried and tried I never felt it, even though I saw the little stars (lumps) in
   pectoral fins.
   2.     To milk the fish for the sperm, the fish has to be two years old or older. I don’t want to confuse the hobbyists because
   the article is for the Tosai fish.
   3.     I didn’t talk about the roughness ( sand paper like ) of male cheeks because that feeling is for two years and older fish.