A Changeling was a Melodie whom was undergoing the Changing Ceremony, an event that occurred on the twentieth year of a Melodie's life. This event involved being immersed in a special pool covered by a blue-green algae which created oxygen through photosynthesis for the Changelings to breathe.
This marked the change from land-dweller to water-breather. The process could take weeks, and the Melodie was vulnerable to attacks from Yavin 8's other predators. The Ceremony was concluded when the gill slits and tail slits of the Changelings were formed, making them adult Melodies, also known as Elders, and allowing them to live entirely underwater.