Dragon Goby, aka Violet Goby:
Quote from CFC:
"The Gobioides broussonettii requires brackish water to survive, when kept in freshwater they waste away and die. They also have a very specialised diet as they are filter feeders which have to be fed with tiny live and frozen foods, bloodworms are too big for them to manage really so baby brine shrimp, small daphnia and frozen cyclops should be used to insure they are well fed and healthy. Because of this diet they generally dont do well when kept in normal community tanks and should really be kept in a species tank"
They get up to 25 inches, so will require quite a large tank.
Another quote from CFC:
"The largest fish a dragon goby can predatate on are fry, they are actually filter feeder that feed in much the same way as whales do by straining water through their gills to collect tiny micro organisms.
When buying a dragon goby you must be careful which one you buy, many of the ones sold in lfs's are Gobioides broussonettii which is a brackish fish and will not live long in freshwater, the freshwater species is Gobioides peruanus which can be identified by its lack of vertiacl dark bands"
I'm afraid thats all the info I can give you