oh wow they found place cells in zebrafish https://www.thetransmitter.org/spatial-cognition-and-navigation/place-cells-help-guide-freely-swimming-zebrafish-larvae/

fish brains don't have any obvious _structural_ analogue of the mammalian hippocampus, but this suggests that the _functional_ analogue evolved very, very early in vertebrates; maybe even earlier than vertebrates (we know octopuses have excellent spatial memory, after all)

also they had to invent a robotic microscope that chases the fish larvae around, that's nifty in itself