I kept G. Polyuranodon in light to mid brackish years ago. Not anymore, but even today I still have some salinity remain in the tank where I keep my G. Polyuranodon... it is now 1.002sg-1.003sg. And guess what, my G. Polyuranodon and my Echidna Rhodochilus is still behaving normally. In fact I am the abnormal one I am the only one in my circle of moray lovers in Indonesia who keep G. Polyuranodon in slightly brackish water.. all of my friends keep them in full FW..