Out in the sea, it's a boat, it's a submarine -- It's Superfish...

This week's episode of Nature is perfect for the seafaring, marine lovers among us. At 7 p.m. Sunday, Superfish swims into the WPT airwaves on both the main WPT feed and the High Definition service.

Everyone who grew up with dreams of being a marine biologist can marvel as Rick Rosenthal follows marlins, sailfish, swordfish and other marine creatures as he explores why their numbers have dwindled during the past half-century.

After getting your toes wet with the TV show, head over to the show's official site, where you can learn about seafood concerns, visit baby sailfish in a sailfish nursery and view a diver's billfish field guide.

And, if your appetite for the wonders of the seas isn't satiated after all that, check out this stunning gallery of underwater photography from National Geographic.