The golden age Aquaman of Earth-Two was just fine swimming with his finny friends and fighting Nazis and pirate to bide his time under the tides. And he used the time to master his communication with the undersea life thanks, in part, due to the knowledge imparted to him as a youth by his scientific father... since he didn't have the natural telepathic abilities that his counterpart Arthur Curry of Earth-One possessed. That Aquaman gained his powers thanks to being born a hybrid of a human father and an Atlantean father. Each Aquaman had numerous adventures in the oceans around the world, with the silver age version joining the Justice League of America while his earlier twin remained a relative recluse aside from occasional appearances alongside the war time All-Star Squadron.
Aside from slightly different color schemes (yellow instead of green gloves and fins for the first Aquaman) and origins, each were cookie-cutter counterparts of the other in most significant ways. They each faced arch-foes with "Black" dispositions... as in Black Jack the pirate and Black Manta the terrorist (and aforementioned arch-foe), with their legions of minions, as well as encountering their closest relation several times... on Earth-One this was the evil Ocean Master aka Arthur's brother Orm Curry, and on Earth-Two the good Sea Sleuth aka Phineas Pike a detective of the oceans and close friend to Aquaman. And of course, their greatest allies were the creature with whom the shared the seas throughout their careers and for whom they often gained the upper hand against their foes. Each endured for decades as their world's premier heroes of the oceans.