This article is from the Aquaria: Good (and Bad) First Fish; Breeding FAQ, by Dean Hougen and Elaine Thompson
I have already mentioned some fish, such as Mollies and Glassfish,
which come from brackish waters - I simply have not called it that
before. Brackish water is intermediate between the fresh water of most
rivers and lakes and the salt water of the Oceans. Brackish water is
found in gulfs, deltas, and lagoons, as well as a some lakes and
rivers. Because brackish water fish need so much salt in their water
they are not compatible with most aquarium fish. Further, brackish
water fish generally need more room per fish to stay healthy than
freshwater fish. Some commonly seen brackish water fish include Monos
- Monodactylus species, Archers - Toxotes species, Scats - Scatophagus
species, and many species of Puffers (family Tetraodontidae).
 
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