Disney creation? No.
Aquatic? No.

Summing up: we are looking for a fictional, carnivorous, single specific animal, which is in part a newspaper cartoon character, and in part an animated cartoon character (we don't know if those are the same parts) and in part comes from written fiction, though "'in writing' is not how one would typically describe its first incarnation." It can be interpreted symbolically, though that's not necessarily helpful, and it is not mythical. Strictly speaking, it's not a mammal (though the audience muttered about that answer). It's neither a Disney creation, nor acquatic.

Was its first incarnation in the 19th century?