A Huddle That Slowly Unravels
Young corydoras added to a tank usually spend their first hours as a single trembling group behind wood or plants, and that tightness is the correct baseline to watch from. Over the following days the huddle unravels by degrees: a few fish sift the nearest patch of substrate, the group relocates together, and individuals begin making short solo excursions before darting back to the shoal. By the end of the week a settled group spends real time in the open.
A group still pressed into one corner, unmoving, at the end of the week is not displaying typical shyness. Check light levels, cover, and whether a tankmate is policing the bottom, because corydoras read as settled or unsettled through the shoal's shape before anything else shows.
Whiskers, Substrate, and the First Meals
Corydoras taste their way across the bottom with sensitive barbels, the whiskers around the mouth. In their first week, active sifting through fine sand or smooth gravel, with barbels intact and busy, tells you both that the substrate suits them and that they are finding food. Food that never reaches them is the week's most common problem: floating and mid-water foods are intercepted by other fish long before anything sinks.
Offer sinking foods after lights dim, placed near the shoal's corner, and watch some of it actually being eaten. A young cory that is feeding well shows a gently rounded belly by week's end. Worn or shortened barbels, by contrast, point to rough or dirty substrate irritating the mouth as they feed.
Those Dashes to the Surface Are Normal
New keepers often panic at a corydoras shooting to the surface and back in a blink. Occasional air gulps are built into corydoras biology and happen in perfectly healthy tanks, especially after active feeding. One or two fish darting up now and then is a quirk to enjoy.
Frequency is the dividing line. If the whole shoal is gulping repeatedly, hanging near the surface, or breathing fast while resting, think oxygen and water quality first: check temperature, surface movement, and test results the same day. Repeated group gulping is an environmental alarm, not a personality trait.
When to Get Help in Week One
Seek an aquatic veterinarian or experienced aquatics shop if young corydoras stop feeding as a group, develop reddened or eroding barbels, show blotches or excess slime, or if individuals separate from the shoal and sit listless in the open. Corydoras tolerate little chemical stress, so a tank dosed casually or with spiking waste levels hits them early and hard.
Also act socially: a shoal that is too small stays nervous all week. Young corydoras are group animals, and adding proper numbers of the same species, once the tank is stable, often transforms behaviour more than any other change an owner can make.
By the End of the Week
A good first week ends with corydoras working the whole tank floor in the evening, resting in a loose line on the sand, and rising expectantly when the lights dim for feeding. Their confidence at floor level balances fish that live above them.
Because their feeding happens after dark and at floor level, shared notes prevent missed meals, and KinsLe Care Teams lets keepers assign the corydoras' evening sinking-food drop and log where the shoal settled each night.