To begin with, I just scribbled lots of ideas down, until I came up with the deep sea secret admirer. That decided, I quickly drew my first sketch.
At first I like it, and was almost ready to go to final, but after letting it sit for a while, I decided I wanted to do something a little less cartoony. I began sketching alternative fish, playing especially with the eyes and mouth. Then I decided to play up the lovey-dovey angle by making the main fish more feminine. (Click on the image for a closer look.)
When I finally found the fish I liked, I plugged them into the original sketch with Photoshop. Then I tightened up the scenery and added the heart-shaped bubbles. Finally, I changed the valentine. I had a sudden inspiration from a Mother's Day card my son made me years ago.