Casey Anthony's Parents Go on Vacation -- What's the Porpoise?!

Just 4 days after Casey Anthony was released from jail ... her parents were kickin' it in the Bahamas ... and went swimming with dolphins -- and for once, there's hard evidence to back up the story.

George and Cindy Anthony went swimming at Dolphin Cay at the Atlantis resort on July 21 ... and spent all sorts of quality time smiling and making kissy faces with a dolphin named Hercules.

As for Casey ... we're told she was not part of the tropical vacation -- but as TMZ first reported, she did enjoy a Corona minutes after she was released from the pokey.