As several people figured out, the design is supposed to represent complementary things: colors (blue and orange), as well as the birds of the air and the fish of the sea. They are opposing elements, but in harmony.
I thought about several different types of placements for the design. The first is an S shape, but I scrapped that one because I didn't like the way the shapes interacted on the shirt. I also tried the bird on top and the fish on the bottom, but I decided that it got the message across better with the two of them "switched" in terms of positioning, and made for a more interesting shirt. I'm glad some people are enjoying the design, I just did it for fun and think it turned out nicely.