Available on DVD: “Fish Tank”

At first the title of Fish Tank is obscure, relating as it does to a 15-year-old’s coming of age in England rather than a literal aquarium.

But as this tough, mesmerizing film takes hold, the metaphor makes itself clear, from director Andrea Arnold’s boxlike framing to the impassive but compassionate way she watches her characters swim in their own murky psychological waters.

Teenage Mia (Katie Jarvis) lives with her little sister and her single mother, Joanne (Kierston Wareing), in a drab housing project in Essex; as Fish Tank opens, Mia is in the midst of an argument with her best friend, fighting with her mom and getting away from her troubles by dancing alone in an abandoned flat. Taking a British realist cue from Ken Loach (Wareing coincidentally made her astonishing debut in Loach’s It’s a Free World), Arnold films the lives of her subjects with fierce, up-close urgency. But Arnold injects her own lyrical touches in Fish Tank that make it more poetic than most films of the miserabilist school: amid a gray post-industrial wasteland Mia may come upon a lone horse, for example, or take a wild digression into a lowland worthy of Thomas Hardy.

The plot of Fish Tank takes off when Mia’s mum brings home an attractive lover named Connor, played by Michael Fassbender with quiet, seductive guilelessness. (Most recently seen in Inglourious Basterds, Fassbender delivered his own breathtaking breakout performance as Bobby Sands in Hunger.) Connor, it seems, might finally give Mia the protection and support she has clearly been missing most of her life.

In many ways Fish Tank joins An Education and Precious as an acute, empathic portrait of a girl growing up, but more than those films Arnold leaves viewers with a feeling of unsettled ambiguity.

Jarvis, whom the director reportedly discovered at an Essex train station, is nothing less than a revelation in a performance that is tender, spiky and utterly fearless in its physical and emotional range.