Corydoras are not a disposal unit
A corydoras catfish should never be fed bread, cheese, milk-based foods, bacon, sausage, deli meats, chocolate, onion, garlic, avocado, crisps and salted snacks, or gravy-covered leftovers tipped in for the bottom. The stubborn myth that corydoras exist to eat whatever falls is how these foods reach them, but a cory is a deliberate feeder with real dietary needs, not a living vacuum for the tank's mistakes. Anything on the never list that sinks will be investigated by a hungry cory, which is exactly the problem.
Barbels and a worm-eater's gut set the limits
A corydoras tastes its way along the substrate with sensitive barbels around its mouth, sifting sand for insect larvae, small worms, and crustaceans. That feeding style puts its face in direct, prolonged contact with decaying food, and barbel erosion is strongly linked to fouled substrate conditions. Rich cheese and fatty processed meats break down into an oily sludge a cory will keep mouthing as it searches, while their salt content burdens a freshwater fish. Bread swells and pastes into the sand where it rots invisibly. Chocolate, onion, and garlic carry compounds harmful to fish, and avocado's fat suits a sifting insectivore no better than it suits any other fish on this list.
Why scraps damage the cory's own habitat
Corydoras groups rest together on the bottom between feeding bouts, so the patch of substrate fouled by leftovers is also their bedroom. A school that spends the night lying on decaying scraps breathes the worst water in the tank at gill level. Smooth sand, which corydoras need so they can sift without injury, also hides soft food fragments below the surface where a gravel vacuum barely reaches. Owners then misread the resulting frayed barbels and lethargy as a mystery illness when the cause is the feeding habit of dropping human food and assuming the corys will deal with it. They deal with it by living in it.
Feeding corydoras the food they actually need
Give a corydoras group sinking pellets or wafers formulated for bottom-feeding catfish, plus frozen bloodworm, daphnia, and finely chopped earthworm-style foods on rotation, fed once or twice a day in amounts cleared within a few hours. Feed after the main community feed, or near lights-out, so mid-water fish do not intercept everything and leave the corys hungry — an underfed cory group is another side effect of the clean-up myth. Plain blanched vegetables can be offered occasionally, but vegetables alone do not meet a cory's need for meaty foods, and seasoned or canned versions belong on the never list regardless.
If corydoras have been eating table scraps
Vacuum the sand surface where scraps were dropped, inspect the group's barbels for shortening or redness, and move to proper sinking foods at set times rather than ad-hoc extras. Watch for corys that stop sifting, sit apart from the school, or flick against the substrate repeatedly. Barbel damage or persistent lethargy in a corydoras is a sound reason to consult an aquatic veterinarian, since bottom-dwellers deteriorate quietly. Bottom feeding is the easiest duty in a shared tank to forget or duplicate, and KinsLe Care Teams assigns the corys' evening feed to a named person who logs it done for the household.