In Splash, Allen is shown going overboard into the sea when he was a child. Allen sees a young mermaid (young Madison) and he is suddenly safe and stays underwater the entire time and remains unharmed until he is rescued.
When Allen is an adult, he jumps into the water after Madison to help her escape. He is struggling to swim until Madison grabs him. During the end credits of the film, it shows Madison and Allen swimming underwater towards Madison's underwater home. Allen does not come to the surface for air the entire time.
Is there any evidence to suggest that Allen can breathe underwater when Madison is with him?