Appropriate fish for 7g nano

I am researching what critters to put in a 7g nano and I am starting to
wonder if there is any fish that is really appropriate to put in it. 7g is
not that large and I don't want to put undue stress on any fish that I
introduce. I am only going to put one fish in the tank, so a loner fish or
smaller symbiotic paired fish is my only choice I believe. I am thinking
either a Watchman Goby or goby/pistol pair or Scooter Blenny might be my
only choices. Any other suggestions are welcome. Thanks.