dragon/violet goby, Gobioides brousonnetti. Esturine fish... Some people find them difficult to feed as some don't adjust to well to captivity, as they are silt sifters to find their food, and so many people target feed them, but sometimes you get ones that will eat prawn etc readily... individuals I guess. I imagine they would do better with a fine substrate, as they are from muddy/silty areas. They get about 55cm, and are the largest goby in the Carribean I think. Yes they probably will do best in brackish.... but they are found in all salinities, and of course changing too. Nice pick up Liz.