Earth-712:

The first Amphibian (Kingsley Rice) was male, and a founding member of the Squadron Supreme. He left the group over their controversial Utopia Project, which involved superheroes taking over the world for the "greater good".

Amphibian's powers allow his body to adapt to undersea conditions; the deeper he swims, the more fishlike his metabolism and physiology become. He also has superhuman strength and stamina which increase underwater.

Supreme Power:

The daughter of "Phil" and "Debbie," not much is known about the second Amphibian, or Kingsley as Dr. Spectrum calls her.

When Debbie was pregnant with Amphibian, she and Phil were driving, probably to the hospital as they had to pull over suddenly and Debbie had the baby then and there. Phil and Debbie both snapped when they saw it, and Phil took off running, while Debbie waded out into the nearly ocean, and tried to drown herself and the baby. Amphibian swam off and wasn't heard from or seen again for a long time, where she met some divers. They freaked out as well. A picture of Amphibian carrying one of the dead divers ashore was taken, and the camera eventually found. It looked as though Amphibian had intentionally tried to kill the divers, and was taken as such until Joe Ledger/ Dr. Spectrum befriended her when the crystal had taken him underwater to recouperate from a fight with Hyperion. It was his vouching for her that got the government to clear up the bad PR, and bring her aboard the Squadron Supreme.

It's presumed the mutation was caused by the nano-virus released from Hyperion's space ship when it first came to Earth.