I love the story about the talking carp, and you're Quite Right about
the procedures for dealing with them; but alas, I cannot believe it.
A talking carp? Maybe. And if I don't balk at that, a talking
prophesying carp is no big step. But that someone should eat a
talking prophesying carp -- no.
That, or there's a missing part of the story where the proper
authorities are consulted (with much finely-detailed argument) about
whether it's kosher to eat a talking prophesying carp, and what are
the precedents; and along about this time one starts feeling tempted
to invent an ancient numinous known-but-to-a-few and =very= oddly
annotated commentary on which mythic and legendary beasts are
permissible to eat, and how to prepare them...
Well, both Leviathan and Behemoth, the mythic and legendary giant creatures of the sea and the land respectively, are kosher. In one Jewish legend of the future, after the Messiah comes back, there's a tent made of Behemoth hide inside which the Behemoth is roasted, and so is Leviathan, and all the Jewish people fit into that tent. The men eat the pretty much inexhaustible meat and the fish. (The women are in the back, giving birth to sons, I was assured by Rachel Pollack, who is the only other person I've ever chatted to who'd run across that one.)
Interestingly, Leviathan and Behemoth will kill each other, which leaves me with several questions about how a giant fish kills a Behemoth in such a way as to keep it kosher.
Making omelettes with the phoenix egg is not recommended. The subsequent fires can cause problems, for a start.