Trying to remember the title of a mermaid movie that might be late 70s or early 80s. I thought it was called the Littlest Dolphin or Littlest Mermaid, but I can't find anything that matches under those titles. A mermaid wants to become human, but to do so, she must stab a human prince (whom she loves) in the heart with a special dagger. She can't do it of course. She has a small dolphin as a best friend. Any ideas?

1975 hans christian anderson's the little mermaid

Don't know the answer but looking for a mermaid movie that the main femaile player played a regular human and also a mermaid that lived in a cave under the house picture started in black and white but the cave and mermaid was in color. Any help is good.