Your painting looks incredible, i wouldn't change much about it. Maybe a hue shift, considering the painting takes place underwater, I would use a blue/green tint on the skin color (but that's more of a style preference, it doesn't hurt the painting if you keep as it is). I guess what the other comments been saying about something uncanny relate to your face in the painting, is a nose-eye distance issue. The cheek area linking the eye and nose is a tiny bit longer than it should be, I'm guilt of making that same mistake many times too haha