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  • Male/Female

    I was wondering how many of you can tell a male and female by the pec fins? Not just guessing but for sure. I would say a koi at least 12 inches
  • #2

    Here's how it was done at Chogorou when I went to Japan. They felt the pec fin for little bumps.

    As for a for-sure method, I dont know.

    What if I put a fish under anestetic, what would be the proper way to press the abdomen to check for milt.
    Attached Files


    • #3

      the shape of the pec will sometimes fool you. the bumbs on the leading edge of the pec is bumpy with males but then their gill plates should be sandpaper like
      as well. The bone is markedly thicker on a male than female.

      with the milt again you need one that is sexually mature. care has to be taken not to squeeze too hard.
      Dick Benbow


      • #4

        Greg, with the fish upside-down, squeeze both sides of the abdomen 4-5 inches in front of the vent between your thumb and forefinger while simultaneously running your hand back toward the vent. Its a milking action. Use about as much pressure as it would take to slightly indent a tennis ball. I usually do it gently once or twice and then use a little more pressure on the final try if nothing has appeared. You will see a tiny bit of white milt at the vent if its a mature male. If the male is "running", some might squirt out.

        You can use clove oil at one drop per gallon to knock them out. Its very safe and you can pick it up at the local pharmacy. Some people cut the clove oil with a little ethyl alcohol (vodka, gin, grain alcohol) to get it into solution quickly and to knock the fish out quickly. I just agitate or aerate the water a bit and wait a little longer for it to do its thing. Its not more than a couple of minutes to knock them out, a few seconds to squeeze them, and another couple of minutes for the fish to completely revive in clean water.

        -steve hopkins


        • #5

          At what point is a male sexually mature? I have been told a few things over the years. I have been told all two year olds are sexually mature, and I have been told any koi over 12" is sexually mature.

          When milking a sexually mature male, do they always have milt year around?


          Keep it simple, keep it straight


          • #6

            Over 2 years in a temperate climate and over 12 inches is probably a safe bet. However, I am not sure they are good breeders when that young. Maybe its my imagination, but they seem to be over-anxious at that age/size, do not take their time to get into position and do not have the weight to give the female a good bump. It takes some timing and coordination to synchronize the release of eggs and milt. They sort of remind me of myself at that point in life.

            Here, males have milt for most of the year. My recollection is that you can only find it in spring and summer on the East Coast. I believe the gonads begin developing in the fall, go into a holding pattern for the winter, and finish development in the spring.

            -steve hopkins


            • #7

              the bumps are the same as for milt- theyll often only show bumbs when in season, ie the breeding season, when the waters warm enough.
              where i live the fish never show milt in winter and only do show milt for maximum of seven months, with most only having it for six. its hard to find a running ripe male early and late in the season.
              ive had running ripe fish still with no bumps and some fish very bumpy with no milt, thats why its not sure fire technique. but by looking for the milt, bumps and also looking for the protruding vent will 99% give you a sex whilst in season.
              the bumps can be on the operculum too and it gives them a bit of grip on the girls belly so they can exert some leverage as opposed to just slipping off and away.
              thats why the girls belly loses its slime and can get worn after breeding.


              • #8

                its not always easy, just because a fish may show no sign of rough pimple like bumps on its fins or on its cheeks does not mean to say that its definately female. just because a fish has no milt after a gentle squeeze does not mean it is female either because they will not always show, ive had males in season that show neither sign until after they are paired up in new water.
                it is funny how overnight with a girl in new water those fish will bump up and milt up, so if the fish is not showing well at first, it sure should after a night with the girls.

                in my male fish its probably around about 50 percent only will show easily with a quick feel for their bumps and about 80-90 percent of my males will show milt with a gentle squeeze.
                Of the fish that dont show bumps and dont show milt, most will have a fat belly and a protruding vent, these are girls. if in doubt (through a lack of protruding vent) i can ussually give a harder squeeze to express some milt.
                a few fish in every hundred i can still not tell easily probably through lack of condition.
                so its in that order that i check.

                1 has fish got bumps (male)
                2 has fish got milt on light squeeze (male)
                or is it fat with protruding vent (female).
                3 does fish show milt on harder squeeze (male)
                if not and still fairly fat in the belly with no protruding vent its most probably a female.
                4 if fish is not showing still and im scratching my head it goes back in pond to spawn next time round.


                • #9

                  I have a Kikisui that I was told it was a male. It's two years old and I'm still not 100% sure it is. I don't want it to be a male. I pulled it again yesterday to feel the gill plate. It was smooth as a baby's butt. I didn't feel any sand paper to it. I will pull it again today to see if I can get any milt out of it. Right now the water temp is 61 degrees in the pond. If it's a male what temp does the pond need to be, before the gills get rough?

                  I was told it was a male because of the nose in it. The dealer said the nose, points a little so he thought it was male. He did try milking it and it had no milt. This is the reason I got it. If it had milt I would have never got it. He wasn't 100% sure on the sex of it so I did get it and I will take my chances on it being a male. I pull it up today I will take a picture of the vent. Maybe you guys can tell better then me. I still think female, maybe that's just a want for me.

                  Here's the koi in question.

                  Keep it simple, keep it straight


                  • #10

                    Nice shape in either event.


                    • #11

                      Boxers, briefs, or thong?

                      Hi Tom,

                      From the photo the Koi looks male,... the body line and the coloration,... but once in a while we get a Koi that is basically "neutral" or undecided,... and can literally go either way as it matures,... not often.

                      At 2 years old, you may find out for sure by May.

                      Best Wishes,


                      • #12

                        whats that got doitsu or something..
                        i couldnt say if its girl or boy from here. i like it though.
                        try get a real close up of the vent. vents only protrude when the female is pretty good to go with eggs, i forget the term thats used. think it starts with a P. it looks like its raised for about 3/4 a circle around the vent. picture a small rubbery clearish thin walled tyre being there..

                        so im thinking your pic wont likely show it well. my water has to be back on the rise (after winter temps of below 14 degrees c) it needs to get up to about 18 celcius before they show easily.
                        i dont know how it is for you but probably around 1 month before everyone tries to breed their first kois in your area you should find one of the signs.
                        ill ussually try and sex all my fish off early so i dont lose any eggs to unwanted spawning in the ponds, if i do it too early in the season i miss being able to tell on a fair few. i cut a fine line between getting a good sexing and losing a small percentage of my breeders to the first day spawning of the season.


                        • #13

                          looks female to me.


                          • #14

                            I tried milking it with no luck.

                            Here's a picture of it's vent.

                            Keep it simple, keep it straight


                            • #15

                              Have you got a koi that you know is a male? If so check it , the females vent is round and the male are somewhat long.


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