A friend of mine told me that with the exception of the Leviasan, everything we might colloquially call "fish" nowadays are merely called "דג" (or "דגה" if its female) in Tanach. I asked several Rabbis and they couldn't think of any other species of fish named in Tanach. Is this true? If yes, why would that be?
I want to know because this friend was using this to explain why Shach Y.D. 107:1 writes that a Treif fish mixed into Kosher fish is Min Bemino if you hold that Min Bemino goes by the name "משום דשם דג אחד הוא." Is that a valid explanation? (Note that Treif fish probably won't be getting mixed into your Leviyasan anytime soon.)