This one of my favorites (it’s so hard for me to choose) because of what I did with
the top and bottom edges. The original poster had a straight edge with flat black at the
top and bottom where there were no fish. The wavy edge I designed for this puzzle is
extremely difficult to assemble, because as each curved edge piece ends, the assembler
has no idea if the neighboring piece continues the same curve or bends back in the other
direction (see the middle wave in the close-up below).
The wavy edge adds a sense of watery movement to the scene.
The black portions inevitably become the last to be assembled,
but are also the most difficult sections of the puzzle by far.
So you finish all the wonderfully-colored fish and are left with a devilishly-tricky
black wavy edge to assemble. It’s like hitting a brick wall.
The number of pieces (1000) isn’t an estimate; when I first counted the
pieces the number came to 998, so I then cut two of the larger pieces in half,
just to reach the nice number of 1000. :-)