Summer is the growth window, and appetite follows the warmth
A koi fry's first summer is when its frame is built. Warm water runs a young koi's metabolism fast, digestion is quick, and a fry in the growing season converts frequent small meals into length and body depth in a way it never will in cool water. The schedule should follow the temperature through the day: a first feed once the water has warmed in the morning, meals spread across the bright hours when the fry are actively hunting, and a last feed in the early evening. On a cold, grey morning the same fry barely feed, and food offered then mostly fouls — so let the water, not the clock alone, set the day's rhythm.
Little and often, sized to vanish in minutes
The working rule for each meal is simple: only what the batch clears within a few minutes, offered several times a day. Tiny, newly feeding fry may need four or more of these small meals; as they grow, the number settles while the particle size rises. Frequent small feeds suit a fry's short gut far better than one heavy feed it cannot fully use, and the water stays cleaner between meals. Step the foods up with the mouths: infusoria and liquid or powdered fry food at the very start, newly hatched brine shrimp as the first real meal for many, then finely crushed and finally small pellets as the fry put on size over the summer.
Colour is revealed by feeding, not painted by it
New keepers are often disappointed that koi fry start drab — many hatch dark and plain, and the patterns they will carry emerge gradually over the first weeks and months. Feeding cannot draw a pattern that genetics did not provide, but good feeding decides how well what is there shows: well-nourished fry in clean water develop stronger colour and cleaner skin, and natural foods such as daphnia, alongside quality fry foods, support colour as it comes in. Judge a young fish in midsummer by its shape, skin and vigour rather than by an unfinished pattern, and expect the picture to keep changing until the season ends.
Grade by size, or the big ones eat the plan
In every batch a few fry — breeders call them shooters — grow dramatically faster than their siblings. Left together, the biggest monopolise food, the runts stall, and past a certain gap the largest koi fry will eat the smallest outright. Grade the batch every couple of weeks: net and sort by size into two or three groups, each fed at its own level. Grading feels ruthless but it is what gives the middle of the batch its summer; without it your result is a handful of giants and a pond of stunted fish. Body shape, the deep, even growth the question asks about, comes from exactly this combination — frequent feeding, room to use it, and no giants stealing it.
Water quality is the ceiling on the whole schedule
Warm water, heavy feeding and fast-growing fish conspire against the filter. Uneaten food and fry waste in summer heat undo a feeding plan faster than any missed meal, so the schedule includes its own brakes: a feed the batch leaves floating is a feed to cut, and regular partial water changes are part of feeding, not a separate chore. Log the day's feeds, quantities and grading sessions as you go; KinsLe's Care Teams holds that summer rota as shared duties, so whoever feeds on a given day can see exactly what the batch has already had and mark their own feeds complete.