Actually this has been dicussed MANY times. From most reports they do not need full sw.
They are brackish really but move into saltwater from time to time for breeding or whatever case.
You can keep them in a higher salintiy just fine. They can tolerate fulll sw though if you really want to do that.
Some guy has had one in bw for 5 years now, pretty awesome set up and he raises the salinity every once in a while.