A saltfish is simply salted cod.
yes it is salt cod.
Salt Fish is any fish preserved in salt, most generally Cod.
Sodium chloride is the proper name for salt.
It is not recommended to mix salt water fish and fresh water fish. It is required to separate the two and provide each with the proper tempered water.
School of fish is quite commonly used but a shoal of fish is the proper name.
There are fish that are commonly called "Bream" in both fresh and salt water.
Fish in salt water maintain osmotic homeostasis by drinking large amounts of water and excreting excess salt through their gills and kidneys. They also have specialized cells in their gills that actively transport salt out of their bodies to maintain the proper balance of salt and water.
The adjective is 'marine'.
I would: it is a proper name/ noun.
Probably salt fish; a salted fish - dried and salt added fish.
Brackish?
There are commonly two types of 'regular' table salt. One is 'Iodised' the other is not. Do not use the 'Iodised' salt in fish tanks. I would advise you to use cooking salt as that is not 'Iodised'.