Amphibian Man

Amphibian Man is a 1962 Soviet science fiction film. It is based on the novel with the same name by Alexander Beliaev. RUSCICO has a DVD release. Different, that's what Amphibian Man is -tragic and beautiful and sweet and strange. It's like a fairy tale. The music plays an important role in the character and plot development.

Youtube has it in parts in Russian with English subtitles. Part 1
The other sections are here.

1000 Misspent Hours says,

It’s kind of like a gender-twist version of “The Little Mermaid,” only with class conflict, mad science, and Russian-language mariachi music— in other words, something the world never knew it had been missing until the day it showed up unbidden on the doorstep.