No, I did not Photoshop the fish into this image. There are some shots that rely on a bit of luck, and this is one of them. But, I've noticed that skilled shooters are "lucky" a lot more often than less skilled shooters. So, maybe there's more to it than luck.
The model, Linda, and I were shooting on the Kittiwake wreck in Grand Cayman. To get the shot I wanted, Linda swam a path we established along the deck, with me shooting. For this kind of shot, it's most effective to have the model in motion, timing each capture based on body position, location and the light (not "machinegunning" – that's what amateurs do). We were just starting a second pass when I saw the fish swimming into the shot out of the corner of my eye (no small feat wearing a dive mask, BTW). I knew I would have exactly one shot to take advantage of this magic moment, and that's where discipline comes in. Don't rush, wait for it . . . . . click.
We finished the sequence, but I knew I already had the shot. A moment earlier or a moment later would have missed. If I'd just mindlessly banged off frames as fast as I could hoping I'd get it, I'd have almost certainly have had two dozen images with the magic moment falling between two of them (something I've learned the hard way). Even when shooting multiple images to get "the one," you don't mindlessly click them off by the dozens; you time each based on what's happening in the viewfinder. Today we capture more frames than we did with film, but shooting so many that you can sequence them into a movie, in most circumstances, points to a lack of skill.
The harder part in capturing magic moments, I think, is trusting that they will come. But, they will, especially if you grow them. When I was less experienced, I was a hunter trying to track down each shot and make a kill. I tried to force these moments because I had to deliver and was afraid to come home empty-handed. Today, I'm a farmer: I set the stage, set the light, and plant "seeds" with my subjects, then wait for them to grow, harvesting the magic moments that I "luck" into. I shoot fewer images than I used to, yet end up with more, better keepers.
So, while the fish swimming into the shot was pure luck, the image wasn't pure luck because we'd set the stage, set the light and planned the shot even without them. When the opportunity came, I was prepared.