There are many freshwater gobies that only grow to 6" but most are predatory and will eat smaller tankmates,one of my favourites is Morgunda morgunda sometimes known as the purple striped gudgeon,a sleaper gobie so not really a true gobie but they only attain a size of around 4",however they are one of the most voracious feeders i have ever seen,similar to dwarf snakeheads in the way they take prey.
A smaller more suitable FW goby is the Peacock goby Tateurndina ocellicauda,only reach 3" max and are extreemly peaceful,can be combined with even tiny fish like neons.
A smaller more suitable FW goby is the Peacock goby Tateurndina ocellicauda,only reach 3" max and are extreemly peaceful,can be combined with even tiny fish like neons.