Can you put fancy goldfish in a brackish aquarium with a dragon goby?
The dragon goby is semi-aggressive, but mainly feeds by sifting organisms out of the mud. In general, like most fish, they will eat anything that fits in its mouth. A fancy goldfish can reach 10″-12″ and a dragon goby can reach 24″. It would seem that once the goldfish reached a large enough size, it would be safe. I would not put a 2″ goldfish with a 24″ goby.