Species decides what full size even means for a corydoras
A corydoras catfish cannot be judged against one adult size, because the group sold under that name spans tiny pygmy species that finish at around an inch to robust bronze and emerald types that reach two to three inches, with females the larger sex. A pygmy corydoras may be fully grown while a bronze corydoras of the same age is barely halfway. The first step in answering the growth question for your own fish is therefore naming the species correctly, since a corydoras catfish labelled vaguely in a shop can leave a keeper expecting growth that will never come — or crowding a fish that will grow well beyond the tank plan. Growth in most corydoras species is brisk for the first several months, then tapers, with the fish essentially at adult length within about the first year in good conditions.
How the growth curve actually runs
A young corydoras catfish adds size fastest while it is foraging constantly and being fed several small meals, filling out in depth as well as length. As maturity approaches, length gains slow first and the fish continues to broaden, so a corydoras catfish can look finished by length while still gaining the deep, rounded body of a true adult. Females become noticeably deeper when viewed from above, especially when carrying eggs, which is a maturity sign rather than continued growth. A corydoras catfish has effectively stopped growing when its length holds steady across a few months of good feeding and its body condition stays full. If growth halts early in a thin, pinched-looking fish, that is stunting or illness to investigate, not a natural finish.
Rearing conditions that shape a corydoras's final size
A corydoras catfish reaches its proper adult size when it grows up with food that actually reaches the bottom, because youngsters in a community tank can be outcompeted by mid-water fish at every meal and grow slowly despite a well-fed tank. Target-feeding sinking foods after lights-out, keeping youngsters in a group so they forage confidently, and maintaining clean water with a soft substrate that protects their barbels all support full growth. Barbel wear is a useful visible clue in a growing corydoras catfish: barbels that stay long and intact suggest the floor conditions are right, while eroded barbels often accompany the poor conditions that also stunt growth. Space matters through water quality rather than magic — a crowded grow-out with rising waste slows youngsters measurably.
Telling a finished adult from a stalled youngster
Compare your corydoras catfish against its own shoal rather than a chart: a finished adult matches the group's mature body depth, rests and forages with the calm rhythm of the adults, and in females may show the broader outline that comes with maturity. A stalled youngster stands out by its narrower body, proportionally larger-looking eyes, and barbels or fins that look worn for its age. Measure length gently by observing the fish against a known mark on the glass at feeding time, and record the figure monthly rather than handling a corydoras catfish, whose spiny fins catch in nets. If several youngsters stall together while adults thrive, review bottom feeding and water changes first, and involve an aquatic veterinarian if condition keeps slipping. Keeping those measurements and species notes together through KinsLe with Family Sharing means anyone in the household can see whether a particular corydoras is still growing or has settled at its adult size.