Betta fry are limited by one blunt fact: a food counts only if the whole piece fits into a very small mouth and goes down in a single bite. That is why their menu changes by size in stages, not by appetite — a hungry fry still cannot manage a food built for a mouth twice its own. The progression runs from microscopic infusoria in the first free-swimming days, through bridge foods a fraction larger, to baby brine shrimp, and finally to crushed dry food approaching a month old. Judge every move up by watching mouths and bellies at feeding time, not by the calendar alone, since fry in one batch grow at uneven rates.
Stage One: Infusoria in the First Free-Swimming Days
For the first two days or so after hatching, fry hang in the nest and live off their yolk sacs, taking no food at all. Once they swim freely and horizontally, about days three to six, they hunt for the first time, and only the smallest life in the water is small enough: infusoria, the microscopic organisms that gather around decaying plant matter and in established fry water. A fry at this stage is barely visible itself, and its mouth is smaller still, so anything you can easily see as a particle is already too large. Offer infusoria several times a day in small amounts, drawn from a culture started well before the spawning, since a culture begun when fry appear will peak after this brief stage has passed.
The Bridge: Vinegar Eels and Microworms
From about day five, and through the second week, vinegar eels and microworms bridge the gap between the microscopic and the merely tiny. Both move in the water, which triggers the fry's hunting response, and both are slender enough for mouths that brine shrimp still defeat. Feed them alongside infusoria at first, then as the main food as more fry take them cleanly, and watch the transition fry by fry: a batch never changes stage all at once. Keep both cultures running before you need them, in rotation, since a crashed culture during this fortnight leaves a size gap with nothing honest to fill it. Uneaten worms sink and foul quickly, so keep amounts small and siphon the bottom gently after feeding.
Baby Brine Shrimp and the Mouth Test
Newly hatched baby brine shrimp enter the menu once a fry can swallow one whole, which for many fry arrives from about the end of the first week into the second, always after the bridge foods rather than instead of them. Test readiness properly: offer a few shrimp to the batch and watch individual fry. A fry ready for this stage takes a shrimp in one bite, swallows without spitting, and soon shows a rounded, faintly orange belly. A fry that mouths a shrimp and spits it out, or worries at it repeatedly, is telling you its mouth is not there yet, and it stays on eels and microworms for a few more days. Feed several small meals a day rather than one large one, rinse hatched shrimp before feeding, and remove uneaten food before it decays in warm, shallow water.
Crushed Dry Food Towards One Month
From about the third week, start offering finely crushed dry food in tiny amounts alongside the live foods — crushed to a powder-fine crumb at first, since fry mouths still set the limit, and increased only gradually in particle size. By about a month, most fry take small crushed pieces confidently as part of a mixed diet, with live foods still carrying much of the feeding. Keep the water shallow, warm and calm throughout, with a lid holding warm, humid air above the surface for developing fry, and keep feeding hygiene tight: several small feeds daily, waste siphoned away gently, and nothing left to rot between stages. Shared among helpers, each stage change is exactly the kind of dated duty KinsLe records through Care Teams, where the person feeding can see which food size this week's fry are actually on.