What healthy growth actually looks like week to week
In the first days after hatching, fry run on their yolk sacs and barely swim; growth starts once they are free-swimming and taking food. From there, healthy fry should never look the same two visits running. Across the first six weeks you are watching for three things together: length increasing steadily, the body deepening behind the head so the fry stops looking like a comma with eyes, and behaviour that fills the tank — fry at the surface, mid-water and near the bottom, all of them mobile and all of them interested when food goes in. Size will vary within the batch, and variation alone is not stunting: it is the shape of each fish, not its rank in the size order, that tells the truth.
The proportions that give stunting away
A stunted fry is out of proportion before it is obviously small. The classic picture is a large head and very prominent eyes carried on a body that stays narrow and pinched, with a belly that never rounds even straight after a feed and a back that looks hollow rather than filled out. Compare like with like: hold the smallest fry's shape up against a sibling's at the same age, not against its size. A small fry with a deep body, a rounded post-feed belly and strong swimming is a late developer who will usually catch up once competition eases; a small fry with the big-eyed, thin-bodied shape is being failed by its conditions right now, and waiting rarely improves it.
Chase the fixable causes first
Stunting in a home fry tank is almost never mysterious. The first suspect is food: particles too large for the smallest mouths, or meals too infrequent for stomachs that empty within the hour, so the runts fast while their siblings feed. The second is water: fry tanks receive heavy feeding in small volumes, waste accumulates fast, and poor water suppresses growth long before it makes fry visibly ill — frequent small water changes with matched, treated water are a growth tool, not just hygiene. The third is crowding and competition, where bold fry station at the food source and the timid ones learn to hang back. Genetics plays its part, but reach for it last, after food, water and space.
Adjust in the order that helps the smallest
Work the fixes from the fry's mouth outward. Offer food fine enough for the smallest in the batch and spread it across the tank so it does not land in one guarded patch; feed little and often rather than rarely and largely. Step up the small, regular water changes for a week and watch whether the whole batch's bellies start rounding better — water improvements show in growth within days at this age. If a handful of fry are powering ahead while others stall, separate by size so the smallest get their water and their unguarded meals; many a written-off runt, given two quiet weeks without competition, grows into an unremarkable fish. What you should not do is compensate with ever-richer feeding in dirty water — more food into a waste problem deepens the very conditions doing the stunting.
Keep a record, because memory flatters
Growth over six weeks is too gradual to judge by eye and mood. A weekly photograph of the batch against the same background, the same corner of the tank in the same light, gives you a strip of evidence your memory cannot argue with, and a one-line note of approximate size and how the smallest are doing pins the picture to a date. That record is also what an experienced keeper needs if you ask for help: 'week four, smallest still thin-bodied despite grading and extra feeds' gets a useful answer where 'they seem small' gets a shrug. Turning the weekly photo and check into an assigned duty in KinsLe Care Teams means the task lands with a named person each week and its completion is marked with a timestamp, so the growth record builds itself as a by-product of the feeding routine.