Though Shaina does have a point that culling should be only used when needed, say you have 100-300 fry that are not deformed, you'll be over run. A good number of them won't have desirable traits.
you have to make sure you CAN cull, for any reason, when breeding. If you have too many you will need to cull to not only make it easier on yourself, but the other fish as well. Finnage can be very important... I bred doubletails and I do not forsee me keeping all of them alive. I will be culling most of them, to bring out only the best of finnage, any genotypes, and some minor finnage "problems".