Are you talking about the Violet Goby Gobioides brousonnetti? They are awesome fish in my opinion! They can be shy, especially if kept separatley. So you don't want to keep them with overly aggressive fish because they won't fight for food. However, these fish tend to be survivors, in my experience, they are good at scavenging food off the bottom. They are a very adaptive brackish water fish. In the wild, some have even been found living in marine strength water. So you shouldn't have to worry much about salinity. I would just go with the requirements of whatever other fish you plan on keeping with them. I would also recomend a large tank to give them plenty of room to swim around. Especially if you're keeping more than one because they will get territorial with one another in tight places:grinyes:
I hope this helps. Feel free to ask any qestions you want. I'm not gonna say I'm an expert. I've just got some experience from keeping these fish for many years.