With corydoras, a good breeder is first of all an accurate one. Dozens of species reach shops under a handful of familiar names, yet they differ in adult size, temperature preference and pattern, so the keeper who breeds and labels exact species is the one to seek out. Aquarium clubs, specialist society auctions and dedicated local breeders are the richest sources, and their fish are usually tank-bred, hardy and already eating prepared foods. Rescues take corydoras in regularly as well, often as the last survivors of a broken-down community tank, and those fish deserve the same careful identification before you adopt.
Why the exact species name is a welfare issue
Corydoras school with their own kind. Six corys of six different species are not a school; they are six single fish sharing a tank floor, and they behave accordingly, hiding more and feeding less confidently. A breeder who keeps species in separate tanks, labels fry with the full species name and can tell you which of the similar-looking spotted or lined species a fish actually is, protects you from building a mismatched group by accident. Ask directly whether a batch is one species or a mix, and walk away from any seller who waves the question off, because for this genus the name is care information, not trivia.
Barbels tell you how the fish has been kept
The whiskers around a cory's mouth are its hands, used to taste food out of the substrate, and their condition is a visible record of the fish's life so far. Healthy fish from a good breeder carry barbels that are full-length, even and intact. Eroded, stubby or missing barbels point to rough, sharp substrate or persistently dirty bottom conditions where the fish was raised or held. Check every fish in the tank, not just the one netted for you, choose plump youngsters that sit upright on the bottom rather than tipping, and prefer fish you can watch nosing actively through the substrate in the breeder's own tank.
Tank-bred or wild-caught: ask, and feed accordingly
A good breeder states plainly whether the fish were bred in their tanks or brought in wild-caught, because the two groups arrive with different habits. Tank-bred youngsters usually accept sinking prepared foods immediately and tolerate a wide range of ordinary aquarium water. Wild-caught fish can be seasonal, slimmer on arrival and slower to learn that a sinking pellet is food, so ask what the batch is currently eating and buy that food for the transition. Neither origin is automatically better, but the honest answer lets you set up the first month correctly instead of discovering a feeding problem fish by fish.
Adopting rescue corydoras into a real school
The typical rescue cory is a lone survivor, and the kindest adoption pairs the fish with a proper school of its own species rather than adding it to whatever corys you already own. Identify the species carefully from its pattern and body shape, ask the rescue what tank it came from and whether its barbels are recovering on smooth substrate, and quarantine before it joins your group. A settled, feeding rescue fish will usually bloom once it has company of its own kind and a clean sand floor to work. Because that identity is so easy to lose on paper, KinsLe Transferrable Profiles carry a cory's exact species, origin and school history from keeper to keeper when its profile changes hands.