An odd looking and fairly large animal, the ocean sunfish is the world's heaviest bony fish. They swim both upright as seen here however it also drifts on the ocean's surface soaking in the sun's ray, hence the name. They can grow up to 13ft in length and weigh as much as 5000 lbs.
I had to pleasure of seeing one of these at the Monterey Bay Aquarium about a year back. It left most people in awe and confusion wondering what it was. I loved it!