Brackish water fish need water that has more salinity than freshwater but less than sea water. The exact salinity level of the brackish water depends on the location. Obviously you will want to keep the fish listed on this page in species or biotope specific aquariums due to their brackish water requirements.
Hexanematichthys seemanni Columbian Shark A fish that can get large! Only keep them in the largest of aquariums.
Tetraodon biocellatus Figure 8 Puffer 15 gallons is sufficient for one figure 8 puffer, with 10 gallons more for each additional puffer. Also, they are easier to keep because unlike the GSPs who need high brackish to marine as adults, the Figure 8's only need a low brackish of 1.005-1.008 throughout their lives
Tetraodon nigroviridis Green Spotted Puffer A good brackish setup is needed for health and longevity of this fish. They should be kept in large aquariums, with no less than 30 gallons per puffer, as they grow to be six inches.