Bruce had heard about the humans holding mers in labs, but he was told there were thare temporarily, and he did see that injured mers were taken and freed later, but them one mer returned sayings they had separate section, one of mers raised in lab, bred to be show dogs to show off, as the king of Atlantis, he wouldn't stand for his people being used as such.

Bruce had his son Dick infiltrate, faking some injury to get in, but once in, he quickly finds and frees the lab bred mers, getting them to Atlantis. However, there was a mer pup, you, alone, the other mers were handed if to citizen to help them, but you? You were practically still a baby, your parents having passed away, so obviously, Bruce took you in.

"That's coral, you don't eat it..."

Bruce spoke gently, taking coral from your hands as he was in the castle garden with you. You were born in a lab, you didn't understand the true sea yet.