a bit of an update. i identified the fish as tetra. glofish, or whatever they be called in particular.
inexplicably, one fish disappeared. literally, no sign of it. one day it was there, the next day gone. i emptied the tank, cleaned it up, washed the stones and shells, fishy nowhere to be found. what the hell. the only logical explanation is that it managed to jump out through a narrow opening in the lid and was then eaten by cats. because i also searched the floor around the aquarium and no dead bodies. as a kid i had a fish tank and occasionally the fish would jump out so i know it can happen.
anyways, i sent miesposo out to replace the missing fish and he came back with two little fellows so now we have three of them. very lively and cute as a button.