Corydoras trilineatus, aka the Three-Line/Three-Banded Cory or False Julii Cory. These catfish have a distinct group of three bands across the flank; two white bands with a black in between. The rest of the body is gray with fine reticulation and spotting. They are sometimes sold as "Julii Cories" but the true C. julii is rare in the hobby, and has much finer spotting.
These are juveniles around 1.25-1.5" long.