A freind of mine had 1 in a 29 for a little with a freshwater flounder and a couple mollies while before moving it into a 55. He called it a Crocodile fish. It just stuck to the glass or under a peice of driftwood upside down (hence the name Crazy fish). Should be a nice peaseful pet but don't trust him with anything smaller then 2/3 his size. They can eat some suprisingly big fish if they want to. Also, adding a little salt may benefit. I've read that they are brackish but tolerate freshwater. he grew about 5 -7 inches but My freind got rid of him after about 2 years. A nice tankmate might be a dragon goby if you have a large tank and desire oddballs for a brakish tank