Time a school that eats at full speed
Zebra danios are overfed when food remains once their famous feeding frenzy fades, and with fish this fast the window is short. A danio school hits the surface like it has not eaten in a week, every single time, so enthusiasm measures nothing. Offer the meal, then time it: a correct ration is gone in roughly two minutes, with the school dropping back to mid-water cruising afterwards. Flakes still floating at that point, micro-pellets sinking past fish that have slowed, or food bouncing along the bottom uneaten all mean you have beaten the school's combined appetite — an impressive feat that takes a genuinely heavy hand.
Tell egg-heavy females from an overfed school
Danio body shape needs one distinction before it can be read honestly. Female zebra danios are naturally deeper-bodied than males, and a female heavy with eggs carries a visibly rounded belly — that roundness is breeding condition, not gluttony, and it comes and goes. Overfeeding rounds out everybody: males, normally slim and slightly more golden than the silvery females, thicken through the back and belly until the school's two shapes blur into one plump outline. Photograph the school side-on against the glass once a month; a whole group widening together across the photos is the ration growing, whatever any single fish looks like today.
Siphon the gravel and count the evidence
What danios miss lands in the substrate, and your gravel vacuum reads it back to you at every water change. A correctly fed danio tank siphons up waste and mulm; an overfed one siphons up recognisable food — softened flakes, swollen pellets — sometimes in surprising quantity from beneath plants and along the back glass where the current drops it. That recovered food is the exact measure of your surplus, and it has been decaying between water changes, feeding cloudiness and algae the whole time. If the siphon bucket embarrasses you, cut the pinch and let the next change deliver the verdict.
Remember the danios are eating the neighbours' share too
In a mixed community tank, zebra danios distort the feeding picture for every species in it. Danios patrol the top and mid-water at speed, so food meant to drift down to bottom dwellers gets intercepted, and a keeper who adds extra 'so the others get some' ends up overfeeding the danios twice — once on their own meal and once on the compensation ration. The danios then show the overfeeding signs first even though they were never the fish you were worried about. Feed in zones instead: danios at one end, sinking food dropped for the bottom fish at the other once the school is occupied, rather than simply more of everything everywhere.
When a swollen danio is not a feeding question
A single danio that balloons while its schoolmates stay slim, a fish that stops joining the feed and hovers apart, pineconed scales on a swollen body, or a danio that grows thin and hunched despite eating is not explained by the pinch size — separate the fish if you can, check the water, and get advice from an aquatic veterinarian promptly. Group-wide plumpness is rations; one fish changing shape alone is a symptom. For the ordinary discipline, KinsLe Care Teams give a zebra danio school a shared feeding record — each meal assigned to a person and marked complete with a timestamp — so the fastest eaters in the tank cannot hustle a second dinner out of a second feeder.