Why Size Differences Matter More Than Age in a Fry Batch
Fry from one spawning rarely grow evenly. A few eat first, grow faster, and then use that size advantage to eat even more, while their smaller siblings hang back and fall further behind. In mouth-sized species the gap can become a safety issue, not just a fairness one, because a much larger fry may chase or even swallow a tiny tankmate. Grading simply means grouping fish of similar size together so each group feeds, swims, and develops without being bullied out of meals by fish twice its bulk.
Sorting Fry Gently, Tray by Tray
Fill a shallow white tray or tub with water from the fry tank so temperature and chemistry match exactly, and set it beside the tank under good light. Net a small scoop of fry into the tray rather than the whole batch at once, because size differences are far easier to judge against a pale background with only a dozen fish swimming in front of you. Tip the largest fish gently into a waiting container, let the mid-sized fish stay, and lift the smallest into a second container, using a soft fine net or a cupped hand for the tiniest ones.
Work calmly and keep each sorting session short. Fry chill and stress quickly in a shallow tray, so sort one scoop, move those fish to their grow-out space, then take the next scoop. If a fish sits between sizes, place it with the smaller group, where it will compete well, rather than with larger fish that could outpace it. Never sort dry-handed, and never leave sorted fish sitting in small volumes while you finish the rest of the batch.
Setting Up Groups That Can Each Eat in Peace
Give each size group its own tank, or divide one larger grow-out tank with a secure mesh divider that water flows through but fry cannot slip past. Feed each group food sized for its mouths: the smallest group keeps receiving fine powdered or newly hatched live foods, while the largest group can move up to crushed flake and larger live foods sooner. Label each group with its sorting date and rough size so the next person feeding knows which food belongs where.
Check that dividers sit flush to the glass and that smaller fry cannot be pulled toward a filter intake shared with a stronger group. A floating plant mat in each section gives shy fish cover near the surface, where much fry feeding happens.
When to Grade Again
Re-grade whenever you can spot obvious size leaders at a glance during feeding, or when smaller fish start looking thin while tankmates look round. For fast-growing livebearer fry that may mean a quick check every week or two; slower species need it less often. Keep notes on how many fish went into each group, because a group that keeps shrinking in number while others thrive is telling you something about feeding access or water conditions in its section.
Watch for torn fins, constant chasing, or fry that hide all day in the smallest group, and separate a persistent bully rather than repeatedly moving its victims.
Keeping the Sorting Rhythm Going
Grading only works as a habit, not a one-off event, because today's even group drifts apart again within weeks. Put the check on the feeding routine itself: whoever feeds watches for size spread, and a full sort happens when that spread becomes obvious. In KinsLe, Care Teams lets you assign the size check and the follow-up sort to specific family members or helpers for each fry group, with completed tasks marked by a timestamp so everyone knows the grading actually happened.