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.
School of fish is quite commonly used but a shoal of fish is the proper name.
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.
I would: it is a proper name/ noun.
The adjective is 'marine'.
There are fish that are commonly called "Bream" in both fresh and salt water.
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'.
Probably salt fish; a salted fish - dried and salt added fish.
Brackish?
I know that the proper scientific name is Exocoetidae.