just a few of my personal thoughts or observations....
your chances of getting any real numbers of fry surviving in the pond are slim. if you want to have enough fry to even consider culling you'll need to seperate them in their own container(s). in a "pond spawn" out of 100s of thousands of eggs that are spewed from the female 1/2 never even get fertilized, out of the half that do, a big percent are gobbled up before hatching. if 10,000 hatch, between defects, them eating each other. the other fish,frogs,turtles,birds dragonflies gobbling them up, and the pump-filtration system claiming its fair share. your not likely left with many after a month. but culling doesnt have to be killing. to cull is to thin out the ones you consider undesireable. you can give them away or sell them... i do cull (destroy) the obviously deformed meaning missing fins or things that would cause them substantially less chances of survival. i ony keep 50 or so koi fry to grow out to sell the next spring. i have noticed one thing tho... what you dont like, someone else will love. i have had customers love fish i thought were ugly, and vise versa. if you want to sell some fish..get a baby pool to use as a hatchery, nursery, and fry pond.. setup a brine shrimp hatchery, and make some spawning mops. if your not raising show quality koi, culling, other than fish with birth defects... doesnt really have to be a concern. if i have 50 - 60 fry i release them into the big pond after about a month. at about an inch long the other koi will stop eating them. they no longer look like larvae and are recognised as fish.