The vibe I get from Del Toro is that the film is completely representational of cinema and the story therein is a secret condemnation of how the evolved movie machine is attempting to destroy the true artistry of film.
The monster being studio greed, represented by the color green.
The protagonists each represent varying degrees of past film ages OR sometimes literal personifications of it.
She's mute - like a silent film. Lives above a movie theater. Both her and Giles have a love for movies. She tap dances and even has a big musical number with The Fish in black and white. Idealistic and romantic and perfect, she's the "Golden Age" of cinema.
“In this movie, Sally [Hawkins] has to look like a real movie star. That was very important for [del Toro]."
He's the middle "Star Age" of cinema. He's an aging, struggling artist who's own profession is dying out due to being replaced by the new thing. Just like the modern actor who's been replaced by special effects and movie franchises. He orders the green pie because he's drawn to the server, like audiences flocked to theaters to see their favorite actor. Ultimately it's acknowledged the pie is awful and that underneath the shiny, attractive shell of the Server there's no understanding or substance.
Not the real villain. But, since he was a kid he's been eating the green candies which has poisoned and twisted him into an evil dude with gangrene. He also hates TEAL and only agrees to buy the car when the salesman tells him it's actually GREEN - color of the future.
He's in charge, so you could make the case he represents the modern Studio Executive who's been corrupted by money and only cares about fulfilling the Studio's will by imprisoning The Fish to abuse, kill and dissect for profit/gain.
Like every good film Director, this guy is responsible for managing The Fish while also having to answer to the Studio Executive about it's progress and follows orders. He attempts to work both sides and remains instrumental in saving The Fish. Ultimately though, in the future, he's ultimately discarded -- no longer needed in a harsh future world full of dissection and analytics and data and void of singular artistic voices.
The Fish is the personification of film artistry itself who's been ripped from its natural beginnings into a harsh place driven by corporate greed. (Fish = Film). In the end of this incredibly romantic ode however, it's art itself that kills the monster and brings back the Golden Age.
"A tale of love and loss and the monster that tried to destroy it all."
It's in this way that by watching (and supporting) this movie you are helping save film artistry, killing the monster.
The movie was originally supposed to be B/W, a nod to classic film.
He told me about this story, saying, “I have this fantastic story. It’s a love story, a girl and a guy, and the guy’s a fish.” And I was like “What?” [laughs] Of course, when it was black and white, I thought, “Wow, this is fantastic, to shoot a black-and-white movie. It’s like in the old days.”