It's a Whale Shark!!
Whale shark sightings are incredibly rare, and we were incredibly lucky to happen upon one. Whale sharks are the largest fish in the sea, reaching lengths of up to 40'. In terms of perspective, the fish on his back is a remora, which grow to be 1-3' long. So this was a baby, but what a baby it was!
If you would like the full size version of this photo (7.6 MB), right click on this link, then pick "save link". (Here also is the untouched original should you want to apply your own underwater filter.)