Why corydoras appetite changes are easy to miss
Corydoras feed on the bottom, often most actively as lights dim, and they eat in company, shuffling through the substrate in a loose group. That makes individual appetite harder to judge than in a fish kept alone: a quiet cory may be pushed aside, may not find food that faster tankmates finish first, or may be genuinely unwell. Before deciding the fish has lost its appetite, watch a full feeding from start to finish at least once, noting whether it searches, finds food, and keeps eating, or wanders over the same ground without taking anything in.
Appetite patterns that merit a vet visit
Book an aquatic vet if a corydoras shows no interest in food for several days despite food being placed right beside it after lights dim, when competition is lowest. A fish that was an eager feeder and abruptly stops, or one that mouths food and drops it repeatedly, also needs examining. Steady weight loss is a strong signal: look from above for a narrowing body and a belly that caves rather than rounding slightly, especially when the rest of the group keeps good condition on the same diet. Appetite loss in several corydoras at once points more toward water or a shared infection, and the whole group history matters.
Signs alongside appetite loss that raise the urgency
Worn, shortened, or frayed barbels with appetite loss suggest the mouth itself is part of the problem, since corydoras taste and locate food with those whiskers. Redness around the mouth or belly, white or fuzzy patches, rapid gill movement at rest, and repeated dashing to the surface all turn a feeding concern into a prompt appointment. A cory that separates from the group, sits in the open barely moving, or struggles to stay down on the substrate should be seen quickly rather than monitored for another week.
Bottom-level checks to run first
Test the water, then inspect the layer this fish actually lives in: siphon a small area and see how much waste comes up, check that the substrate is smooth rather than sharp enough to damage barbels, and confirm sinking food is reaching the bottom in the cory's area. Review whether a recent medication, a new tankmate that outcompetes it, or a change from one sinking food to another coincides with the change. Photograph the barbels and body shape weekly so slow decline is documented rather than guessed at from memory. Also note whether the fish still joins the group at dusk, because a cory that feeds a little but has stopped schooling has changed in two ways, not one.
Information that helps the vet help your corydoras
Bring the timeline of the appetite change, whether companions are affected, your recent water results, what foods you offer and how you feed them, and clear close photos of the mouth and barbels. Note any substrate change or new additions to the tank in the weeks before the change began. Keeping those feeding notes, photos, and test results filed in KinsLe's Pet Passport gives the vet this corydoras's bottom-dwelling history in one organised place.