The Honest Answer: Five to Eight Years, a Decade Possible
The corydoras family covers well over a hundred species, and lifespan varies with size and species, but five to eight years is the honest central figure for the popular aquarium kinds, with well-kept groups of the hardier species, bronze and sterbai among them, documented beyond ten. That is a substantial life for a fish an inch or two long, and it reframes the purchase: the chirpy group sifting the sand in the shop is not a garnish for the tank but one of its longest residents, likely to outlive many of the tetras above them. It also means the losses people shrug off in a fish's first year are not the species being short-lived; they are husbandry failures with a long shadow, because a corydoras that clears its first settled year is usually set for most of a decade.
Sand, Barbels and the Bottom of the Tank
A corydoras experiences the world through the barbels around its mouth, sifting the substrate for food, and the floor of the tank shapes its whole life. Fine sand is the surface those barbels evolved for; coarse, sharp gravel wears them down, and eroded barbels invite infection and make feeding painful, quietly shortening lives that should have run for years. Keep the substrate clean as well as soft, because this fish lives face-down in the layer where waste settles: a neglected bottom is a bacterial soup at exactly the height a corydoras breathes and feeds. Gentle, regular vacuuming of open areas during water changes, without constantly uprooting the whole floor, keeps their world hygienic. Add smooth hiding places, shade during the day, and open sand for the evening's group sift, and the floor becomes the safest storey of the tank instead of the dirtiest.
Company and Food That Reaches Them
Corydoras are social in a way that is visible within minutes of watching a proper group: they rest together, forage together and startle together, and a lone corydoras in a community tank is a subdued fish living under permanent low-level stress. Keep at least six of one species, since mixing single specimens of several kinds looks varied to us but leaves each fish effectively alone. Feeding is the other quiet determinant of their span. The myth that corydoras live on scraps and algae starves more of them than any disease: they need sinking foods of their own, wafers, pellets and small frozen foods delivered to the floor, ideally some of it after lights-out when the mid-water fish are asleep. A corydoras group with plump, rounded bodies and intact barbels at year two is a group on course for year eight.
Keeping Track of a Long-Lived Group
A group that lives a decade changes slowly: individuals age, numbers dwindle, replacements join, and the details of what worked, which foods they took, what the water ran at, are easy to lose. Noting the group's history as you go keeps those years useful long after the details would otherwise fade. And when a question about their remaining years comes up mid-week — a torn barbel, a food change, a new species to add — put a follow-up question to KinsLe's Kinny; he answers using the KinsLe Answers library.