The ancient Greeks certainly distinguished between dolphins and fish. Whether they knew dolphins, unlike fish, were air-breathing, does not seem easy to establish however. The Greek term for whale , giant fish or sea monster was the same one, apparently (κῆτος) and this is what has led to Jonah's tale being sometimes referred to as involving a fish and sometimes a whale: https://en.wikipedia.org/wiki/Cetus_(mythology) The original Hebrew was fish, though. Interesting. I did not know that.