"Some fish fly."
Translation:Einige Fische fliegen.
Again, a bad translation. Without further context, the statement refers to some species of fish. The correct translation is:
"Manche Fische fliegen".
"Einige" would be used to indicate a few fish from a larger group made up of individual fish, regardless of their species.
"Ein paar" is closer to "a few" or "a couple" rather than "some." "Some" sounds like more than "a few" to me. They aren't the same phrase.
etwas on its own means "something"; before an uncountable noun, it can mean "a little bit of..." as in etwas Wasser "a little bit of water; some water".
You can't use it before countable nouns. "Some fish fly" has the plural countable noun "fish" in it.