Culling is the hardest part in oranda breeding. This neck breaking job is the one I hate most. Its not because its hard to do but you are force to destroy lots of fry. But I should accept reality because if I will not cull, my stocks will all out off quality and it will degrade overtime. I had to select the best of the best.
How many times I cull? All the time. I start culling when they are 5 days old. I destroy all deformed fry. Since deformities are hard to see during this age, I just cull all single tailed and blind which includes one eyed fry. The pictures will tell which of which are good quality. Then the next culling is after most of them changed colors. I destroy all white/bronze color no matter how good they are. This is because I don't have space to keep them all. Also you can seldom sell them and the price is cheap. Also white or bronze orandas are mostly no or little head growth. The color I keep are red, red & white and red cap orandas. Black orandas are harder to breed because most of them change their color to bronze. And by the time you will know that they are bronze is when they are already big and for me its really a waste of time and money if you will destroy a fully grown fish.
Then during growing period, you will cull all those with tailed defect. The tail should be perfectly spread and should be 4 pork tail and split in the middle. Also you will cull those with inverted gills. Some fish will also die from other reasons like disease or swim bladder defect. My estimate is, in my 1 thousand fry only 100-150 will end up in the market. This includes Grade A(very high quality), Grade B (high quality) and Grade C (low quality). Grading should be done on the same age. Its not fair if you will compare the 1year old (tosai) to 2year old (nissai). The older the fish the more beautiful it is.
The grade of the fish usually depends on who is looking. My grade C, for most people is already beautiful. How about more if you will see my grade A. That is why culling is necessary. This maintains the quality of your stocks.