Katie Jarvis plays teenage Mia so believably it's as if writer-director Andrea Arnold pulled her right out of the brutal world of UK council estates where Fish Tank is set. Mia's accent, her hair, wardrobe, walk, and expletive-laced dialogue: all of it taken together gives us the impression of a character so complete, so real that Katie and Mia become one. We are no longer watching a character. We are watching a real person.
Jarvis' non-performance, her on-camera naturalness, makes watching Fish Tank unsettling. It's as though we are are spying on a real person. And we feel guilty because we're able to experience her world without taking any of the risks that she herself must. The reality that Arnold presents is harsh. Mia and her mother and younger sister are poor, and while not completely miserable, they definitely treat each other miserably. There is no mention of Mia's father. And judging from how casually her mother has boyfriends stay over, we assume there's been a steady procession of men through their life.
But Mia has an escape. Every day she hides herself away in an empty apartment, along with a portable stereo and a two-litre of some kind of alcohol, where she practices her own dance moves choreographed to hip hop music. She emulates the music videos she sees on TV, videos with shaking asses and exploding sexuality. But strangely, almost innocently, Mia's dancing is not to entice. Instead it's done for herself, for her own pleasure. And while her moves are often generic and even banal, Arnold shows Mia dance with such sincere intent, that we can't help but take her seriously. Perhaps her belief in her own talent will take her somewhere better.
It's this contrast between Mia's world of violent bitterness - adolescent disdain on steroids - with her world of escape that gives us a sense that Mia has a plan. It makes everything about her life a little less dismal when we see her try so hard, when we see her want to get the hell out of there. We hope along with her.
It's Mia's capacity to desire and build something good for herself that makes us see the entry of her mother's latest boyfriend - played by Michael Fassbender - as something significant. Connor is different. He is beautiful, funny, and sincere; a breath of fresh air. And despite the way Mia sneers at him, we understand this is the only way she knows how, that she in fact feels differently, and her challenge is to learn how to overcome the fear to express it. And it doesn't hurt to have Fassbender at his charming best as your motivation. The sexual tension between them is both shocking and understandable. Who wouldn't be tempted? After being surrounded by bleakness your whole life, to give-in to such a positive force would be a rational choice. Connor's capacity to build happiness is seductive.
Considering the world she comes from, Mia's naïveté is, on the one hand, unexpected, but it's also another reminder that she can hope. To hope despite, also, the world she comes from. Arnold presents us with a paradox. It's Mia's innocence that let's her dare to leap frog out of this life to another, to a place of experience. Of experience that is chosen, not determined.