Mermaids of Tiburon (1962)

The titular Mermaids of Tiburon are women who spend most of the movie underwater, topless and in thongs. There is no full nudity, while their full breasts and butts are frequently shown. While the main character/narrator mentions in passing that he has "more than a scientific interest" in them there is no sex.

A mermaid is hit in the stomach by a spear. Some blood shown.