Culling fry seems very simple in my head, but as I have found out many times before, things that work great in theory don't always work in practice.
This is our first culling session - we had recovered a BUNCH of koi fry from a pond rescue. Only some of them are shown in the white pan, we had hundreds more that we sorted through.
Being the first time, we were having a blast, but it took us almost all day to sort them. We would put the maybe koi fry in one bucket, and the rest back in the adoption tank, then sort those maybe into a smaller number of maybe, then sort them again to get down to just a few we were going to keep.
Then I had a batch of my own koi fry, and I started with literally a couple thousand. After a while of just having them in the tank, their numbers started dwindling fast and I learned how quickly tobie koi develop. A tobie is a koi that grows faster and larger than others, and eats his brothers and sisters. So if you want to have more than just a couple of big fry, you need to sort them almost on a weekly basis to seperate the tobies from the small ones.
To dig them out of the tank, I pump all the water out with a fine mesh over the pump intake so the fry don't get chewed up by the pump impeller. Next I had a series of buckets setup with airstones in each one. I'd net a few, put them in the shallow bucket to examine them, divide into the different buckets and continue.
Here my girls are doing a sorting.
The process of culling with multiple buckets & containers has a number of problems. Each container only holds a small amount of water and so the temperature starts to change in each container, and when moving them from one container to the next, I wonder if I am shocking the fish. Also they run out of oxygen in the smaller containers, and start to gulp at the surface. And when going thru so many, I tend to sort them into a container, then think "hey, lets take another look at that one", and would have to dump the entire container to get all the fish back into the sorting bucket.
So I looked at all sorts of videos of real japanese koi farms on Youtube, and tried to figure out their culling process. They sort thousands of fish a day, so surely they had a technique that I could mimic?
Found one video that had a bunch of guys hunkered over various tanks, and the fry were in nets which were partially submerged in the tanks. What perfect way to sort fish, solves all my problems, why didn't I do this way first?
So I setup a barrel and used some of my nets to hold the fish temporarily as I sorted them.
Couple of days after doing the video above, I found a great koi culling tool -- a laundry sorter!! Its basically some pvc pipe with little knob fittings that stretch open 3 laundry bags. Fits perfect over a green tub that I have.
The other improvement that I discovered was holes in the side of my sorting bucket. I drilled a bunch of holes 2" up from the bottom. This lets me scoop up more baby fry with the butter tub, dump it into my sorting bucket, and the excess water drains itself back into the green tub. Before I was dumping the excess water, and every few cycles a couple of fry would go over the edge. As soon as I find a nice blue bucket, I'll convert one of those and use it.
As for the nets used to catch and sort the fish, I started with the blue and green net in this picture. The fry kept getting stuck in the corners of the nets and I had to invert the net as I sorted, which takes a lot of time.
I had seen a number of pictures of japanese culling with these nets that looked like a soup ladel. I searched on the web and found one for sale, yea, it was a couple hundred bucks !!! YIKES!! So I made my own.
First I made a wire hoop and then used kite string to tie it onto a stick. I also put a lot of Titebond II glue on the stick before hand, and then smothered the string in more TB2
After the string dried, I put the net in a clamp to hold it, then put a bead of Titebond II glue around the rim of the hoop. Then I wrapped some mesh around the hoop, and sat this tennis ball in the hoop to give it a shallow bowl shape. The tennis ball is wrapped in a plastic bag to keep the glue from sticking to it. It works GREAT!!! Very easy to sort fry in my shallow bucket with this.
By the way, the mesh part of the net came from a camp chair. I saw one in the trash after one of my daughter's football games, and it had a cup holder in it -- just looked like the perfect size mesh so I cut the cup holder out and used it.