As a medrash it is not taken literally. Also the point is that the fox is lieing in order to con the fish into being victims and allow the fox to easily catch and eat the fish.

The fox is lying to con the fish, yes, but is it a plausible lie (they actually did previously hang out together somehow, so maybe the fish is more likely to believe it) or a bald-faced lie (that never happened)?

I would say that the point is that the mashal of water being torah is what is important. That is that the fish will die out of the water just as the Jews will die if they try to survive without Torah and the fox are those who try to get the Jews to leave the torah. Obviously it could never have happened in literal terms.

@MonicaCellio As a mashal one can say (as in the hagadah) our ancestors (before Avraham) were idol worshipers and they nations are attempting to convince us to become idol worshipers again.