I remember reading somewhere (either from a book borrowed from the library, or in a footnote in T. H. White's "Beastiary") that the Hippogryph -- the offspring of a horse and a gryphon -- first appeared in literature as a satirical joke. You see, back in the day, it was believed that gryphons ate horses as their primary prey. So the idea that a horse and a gryphon would be sexually attracted to each other enough to mate and have an offspring was considered the most impossible of impossible things (think "Horefeathers!").
So, once, a writer (forget who, forget when) wanted to make a point that alchemy / magic was nonsense, so he wrote an epic where there was an alchemist who rode a hippogryph.
Somewhere along the line, people forgot the satire, and took hippogryphs seriously, as a magical animal (Hello, Harry Potter).
Anyway, I figured that the combination of fish-cat would have a similiar connotation for people today.
...I was going to give it bird's wings too, to make it really odd, and also to color it in with more texture with scales and fur, and feathers. But getting the shapes right was so fiddly without a proper mouse that I ran out of enthusiasm and energy by the end...
Oh, well...