Dragon gobys are brackish water fish. Yes, they can be in FW
, but they don't last long. A little known fact about them: they are wild caught in BW then thrown into fresh by the folks who catch them. And I mean literally thrown into fresh, no acclimation or anything. IF they survive, then they get shipped out. Once shipped out, they are again placed into the wrong type of water. They will start sloughing off their slime coat and become more vulnerable to disease.
Also, the goby will eat smaller shrimp.