A single koi spawning can produce thousands of eggs, and the first season is shaped by that number. Fry need their own protected water, foods that grow with them, and repeated honest selection, because keeping every fry guarantees poor water and stunted fish. Owners who decide their keeping capacity before spawning make calmer choices at every round that follows.
Give Fry Dedicated Water Away From Adult Koi
Set up a fry pond, vat, or large tank with mature water, gentle filtration that cannot draw fry in, and a cover or net against birds, cats, and dragonfly nymphs hunting from plant stems. Adult koi eat eggs and small fry, so spawning media carrying eggs should move to the fry water, or adults should move out, before hatching. Eggs typically hatch within roughly two to four days depending on water temperature. Fry cling to surfaces at first, living off a yolk sac, and usually begin swimming and feeding a few days after hatching. Keep stocking light from the start, since fry grow fast and water quality falls quickly in crowded fry water.
Feed by Size, Several Times a Day
First foods must be microscopic: infusoria-rich green water or a liquid fry food offered in small amounts several times a day. Within the first week or so, active fry can usually take newly hatched baby brine shrimp and finely powdered fry food, and bellies should look full and rounded after feeds. As weeks pass, move through crumbled grades of fry food, increasing particle size only when even the smaller fry in the group can still eat comfortably. Feed little and often through the warm months, test the water frequently, and change small volumes with matched water rather than letting waste build between larger changes. Uneaten food fouls fry water faster than fry themselves do.
Keep a simple batch note beside the fry water: hatch date, food grade in use, and date of the last water test, updated at the evening feed.
Grade by Growth So Slower Fry Still Feed
Koi fry grow at uneven rates, and larger fry will eat smaller siblings once the size gap widens. Grade the batch with a soft net and a viewing bowl every couple of weeks, grouping similar sizes together where space allows. Grading is not selection yet: it simply keeps food competition fair and prevents losses that have nothing to do with quality. Weak, deformed, or persistently failing fry should be removed promptly and humanely, and a local aquatic shop or pond club can advise on humane methods and on rehoming routes for healthy surplus fish. Numbers should fall steadily through the season by plan, not by crisis.
Choose Keepers as Colour and Pattern Declare
Colour and pattern develop gradually, so selection happens in rounds rather than on one day. A first selection at roughly four to six weeks can remove fry with no pattern promise for the varieties you breed, while later rounds through summer judge pattern edges, colour depth, and body shape as features firm up. Judge keepers in a shallow light-coloured bowl, in daylight, against the space you actually have for winter and beyond. A modest pond holds only a handful of adult koi well, so keeping a dozen strong juveniles beats keeping fifty crowded ones. Rehome the remaining healthy fry through clubs and shops while they are still small and easy to place. Listing each grading date, selection round, and daily feed in KinsLe via Care Teams keeps the season's decisions visible to everyone who helps with the pond.