In my last post, I reviewed the reasons and general methods for culling fry, and as a follow up post, I want to raise some important considerations about fry density, and best culling practices under different circumstances. Certain, breeds or types offer the advantage of having distinctive traits that can be selected for at a very early stage. Personally, I think these types are the most satisfying for the hobbyist breeders. If you consider that commercial goldfish farms aim to produce large numbers of fish of consistent quality, then by default, any fancy breed that is more difficult to produce in quantity should be prized by the smaller hobbyist breeders. Hobbyist breeders can enjoy the satisfaction of breeding and owning small numbers of spectacular specimens that could never be devalued by mass production. For instance, the correct tail shape of the Japanese Ranchu is difficult to produce in large numbers, but fortunately, this trait shows up very early on, and so the best fish can be selected early enough that resources need not be wasted on inferior fish. Similarly, scale types can be segregated at an early age, so with calico colored fish, the metallics and possibly the pinkie matts can also be culled at an early stage. By netting individual fry and looking for the metallic sheen on the scales, along with the metallic iris, these wild colored fish can be culled.
Ranchu fry are now five weeks old, and have been selected for tail shape
The breeder should keep in mind their space limitations and the time frame for growing their fry to salable size under ideal growth conditions. If the total grow out space is a 40 gallon breeder tank or similar sized tub, then realistically, only around 10 to 20 fish can be grown out to the 2″ size given the space constraints. In the early stages, it is beneficial to reduce the fry to a manageable number, such that enough brine shrimp can be produced on a daily basis to keep all fry well fed. However, it is also beneficial to keep enough fry that they will school, swim continuously, and feed competitively. When there is some competition for food, superior fry may stand out as faster growers or better swimmers. If there are too few fry, some food may go uneaten and cause water quality problems.
Consider how much baby brine shrimp you can reliably produce on a daily basis
For culling, I like to use three bowls, which hold unculled fry, definite “keepers”, and definite culls. I scan the bowl of unculled fry for both the best quality fish (keepers) and the obvious culls. If the keepers bowl is quickly filled to the target capacity, then all the rest can be culled. If there aren’t too many obvious keepers, then I focus on removing the definite culls, and reduce the numbers that way. Sometimes, it may take awhile longer to be able to identify the best fry.
Consider space limitations when determining how quickly to cull fry
A few pointers on what to keep and what to cull… while it is usually safe to cull the very tiny fry that aren’t keeping up with the rest, I would not advise keeping only the largest fry. Many times, the largest fry can appear less refined as they get older, and the best fish often come from the average sized fry. Pay special attention to the swimming ability of each fish; don’t be seduced by large tails if the fry is already having trouble swimming properly. You will learn a lot by studying your own lines over time, and you will gain an understanding of how different fry attributes develop as the fish grows. Take pictures of your fry at different ages; these will be a useful reference for the future. Be careful not to bias your selection too much toward traits you are unsure of, as fry do change as they develop.