Just about how many fiddler crabs do you think one could comfortably keep in a 10g?
Like this one?:
Like this one?:
FS is correct!That's not much real estate for fiddlers, but if you have the proper brackish setup I'd say you could fit a max of one male and two females. You want at least two females per male in any setup to spread out the male's attention between the ladies and prevent excessive harassment.