"You eat a fish."
Translation:Mangiate un pesce.
"Tu" is the second person singular, whereas "voi" is the second person plural. Each has a different conjugation, similar to Spanish and other Latin languages. In English it's just you for singular or plural, although in some parts of the country people would say you all or y'all... haha.
Hi! In English "you" can be singular or plural, depending on the context. "You all" is a colloquialism, mostly heard in the South, but not grammatically necessary.
Speaking to one person: "Hi Mom! When did you get here?"
Speaking to multiple people: "Hi Mom and Dad! When did you get here?"
Same exact sentence - "When did you get here?" In the first one, "you" is singular (to one person), in the second one, "you" is plural (to multiple people).