I'm thinking about getting two Fiddler crabs.
In one of my 10 gallon tanks, I have about 6 Neon Tetras, 4 Orange Von Rios, and 1 Amano shrimp. Have some Frogbit floating around and growing, some Java fern, the rest a is all fake.
So, they say Fiddler crabs may do better in slightly brackish...