I have a Dragon Goby (approx. 12") in a freshwater 125g with an Armored Bichir, Ghost Knife and Fire Eel. Before y'all say anything, I know they thrive in brackish long term and this is a TEMPORARY situation until I finish his own br tank set up (about another month left for tank stand build). That being said, everybody gets along
swimmingly. It's been 8 months that he's been with the gang in there. He is definitely a no-****s-given fish and will bump anyone out of the way when he's mid excavation in the sand. If he wants where they are, he'll just wiggle his way onto them and wiggle harder until they move off. They don't fight. He's too busy destroying my whole tank setup to worry about anyone else lol