고래는 포우류지 어류 아닙니다 -
I've heard that here, 지 is a contrastive (like -지만), so the meaning should be 'A whale is not a fish, but a mammal.'
However, I'm more used to '지' meaning 'isn't it?'. So I might read it as 'A whale is a mammal, isn't it? It's not a fish'.
Could either of those interpretations be correct? Or can '지' not mean 'isn't it?' when it's not at the end of a sentence?