their tiny (full grown 1 inch) brackish water carnivores. alot of places sell them fresh water, but they wont last long that way... need salt. Mine LOVE frozen brineshrimp and blood worms... and will hunt mollie fry, but I havnt seen them catch anything yet. (but the last time I put fry in there, the gobies were about the same size!)
I just adore them.. their supposed to be shy, but mine are right out front, demanding food.