I have been researching brackish fish and or "brackish tolerant fish" for a little while now.....Puffers: green spot, ceylon, figure eight are the poplular brackish ones...some say the green spots need to be in full marine at about 4"...Violet gobies they also classify as brackish because they can be found in the gulf of Mexico area....Many cichlids and or tilapia are brackish or marine some say also....Mayans, cubans, Hatiaens, some central american cichlids are "brackish tolerant"....Several tilapia can be kept, I personally have had a Buttikoferi thriving in 1.016 SG for about 3 months now...If you check fishbase for a certain fish and sometimes it may state they are found in bracksih waters or venture into marine habitats often for feeding or breeding they can be kept in brackish waters......My tank has Australian rainbows, native Fundulus, columbian sharks, Green spots, Violet goby and the Buttikoferi with and SG around 1.016....BTW you can google the name Nealle Monks, he is probably the formost expert on Brackish aquaria....