Empire is celebrating films of the 80's this month and one of their feature films is one of my favourite mermaid films; Splash.
Daryl Hannah talks befriending fish and underwater kissing as well as how needing a loo break could hold up filming by a whole day.
Once Madison’s mermaid costume was on, it was on for the day. "If I had to pee, that would ruin the entire day's shoot because it took so long to put on and take off," rues Hannah. "My circulation would be gone in my extremities, so it took a while before I could walk again. It made me very sympathetic to fish! I remember when I was filming the scene in the lab tank I was very upset about a big fish that was being kept in a smaller tank."
http://www.empireonline.com/movies/features/daryl-hannah-shares-secrets-splash/