Mia Williams is a volatile and socially isolated 15-year-old. She lives on an East London council estate with her single mother, Joanne, and younger sister, Tyler, and is highly antagonistic toward both of them. Mia is a loner, appearing to have had a falling out with her best friend Keely. She provokes Keely's other friends, criticises their dance routine, and head butts another girl. Mia regularly practises hip-hop dance alone in a deserted flat.
Near the estate, Mia comes across a skinny, tethered horse in a Traveller encampment. She tries to free it, only to be caught, taunted, and assaulted by two young men, the horse's owners. A third young man, Billy, the brother of the other two, is more sympathetic. He shows kindness towards Mia and explains that the horse is old and ill.
Joanne's new boyfriend, Conor O'Reily, is a charming and handsome Irishman. He compliments Mia on her dance moves, invites Mia and Tyler to come with him and Joanne on a day-trip into the countryside. He introduces them to his favourite song, Bobby Womack's version of "California Dreamin'", and shows Mia how to catch a fish using noodling. Although Mia is abrupt with Conor, she appears to be intrigued by him.
At an internet café, Mia watches amateur breakdancing videos on YouTube. As she is leaving, she finds and steals a flyer for a club seeking dancers. Keely's friends enter and they exchange taunts. Accompanying Billy, she sneaks into a junkyard where he steals a car engine part. Mia visits Conor at work, as a security guard at a hardware store. Conor encourages Mia to apply for the dancing audition. He lends her a video camera to record an audition tape. Their interactions continue to be flirtatious. After giving Mia the camera, Conor puts on cologne and leans into Mia while asking what she thinks of it before suddenly administering a spanking for running off when a social worker visited. One night Mia secretly witnesses Conor and Joanne having sex. Mia then goes back to her room and slams the door several times. Mia sends in her tape and is invited by the club to perform in person. Late one night, with Joanne passed out drunk upstairs, and after Mia and Conor have both been drinking, he asks to see her dance routine in the living room. When she dances to "California Dreamin'", Conor then invites her to sit next to him which leads to them having sex. Before returning to Joanne's bedroom, Conor tells Mia to keep their liaison a secret.
The following morning, Mia hears her mother crying, Tyler tells her that Conor has left. Mia tracks him down to his home in Chadwell St Mary and confronts him. He explains that he cannot see Mia any more because of her age. He drives her to Tilbury Town railway station and provides her fare. Changing her mind, Mia comes back to his house and sneaks in through the house's back window. Finding a video camera and watching it, she discovers footage of Conor's wife and young daughter, Keira. Mia then urinates on the living room floor and, hearing the family return, sneaks out of the back door.
Watching Keira riding her scooter on the house's road, Mia impulsively pressures Keira to go with her under the claim that Keira's mother told Mia to take her for ice cream. Going out into the fields and reaching the River Thames, Keira tries to escape. Mia catches up with her, but in the struggle, Mia throws Keira into the turbulent river water, disappearing and resurfacing after a moment then Mia pulls her out, and takes her home as night falls. When walking along a street, Conor's car screeches to a halt beside her. Mia runs away and Conor chases her over a field; when he catches up with her, he slaps her, knocking her to the ground, and then walks away without saying a word.
The next day, Mia goes to her audition. It is immediately obvious that it is for erotic dancers. The other participants are all grown women wearing heavy makeup and provocative clothing. Mia takes the stage wearing a hoodie, but as the music starts, she walks off before performing her routine.
Mia goes in search of Billy. When she arrives at his place, Billy tells her that the horse had to be put down. Mia sinks to the ground in tears. Billy says he is moving to Cardiff, Wales, and invites her to join him.
Mia returns home to pack. Her mother tells her "right then, piss off" by way of a good bye. Mia, for once not lashing back, silently joins Joanne in dancing to Nas' "Life's a Bitch", matching her movements. Tyler joins them. Mia goes to Billy's car after hugging Tyler goodbye. The two set off for Wales as Tyler chases after the car.Katie Jarvis as Mia Williams
Kierston Wareing as Joanne Williams
Michael Fassbender as Conor O'Reily
Rebecca Griffiths as Tyler Williams
Harry Treadaway as Billy
Sydney Mary Nash as Keira O'Reily
Sarah Bayes as Keely
Katie Jarvis, who plays Mia, had no prior acting experience. She was cast for the film after one of Arnold's casting assistants saw her arguing with her boyfriend in Tilbury Town, which is the railway station featured in the film.
Principal photography began 28 July 2008 over the course of six weeks, and was filmed in chronological order. At the end of each week the actors were given the scripts for the scenes that they would perform the following week, so that when they performed each scene they were largely unaware of what would happen to their characters later in the film.
Music features prominently in the film, particularly connected with Mia's dancing. The song she uses at her audition is "California Dreamin'", as covered by Bobby Womack (1968). The CD she borrows from Conor is The Best of Bobby Womack (2008), on which "California Dreamin'" appears on track 17, as Mia requests. Towards the beginning of the film, the song "Me & U" by Cassie is also used and the video for Down 4 U by Ja Rule and Ashanti is watched by Mia when she first meets Conor. Other songs include "Jah Rule (w/ Paul St. Hilaire)" by Rhythm & Sound (Album: W/The Artists), "Life's a Bitch" by Nas, "Just to Get a Rep" by Gang Starr, "Cool Down the Pace" by Gregory Isaacs, "Your House" by Steel Pulse, "Juice" by Eric B and Rakim, "Baby girl" by Wiley, "Show Me Love" (Stonebridge Club Mix) by Robin S, "Get Up Offa That Thing" by James Brown, "In The Fading Light" by New Device, and "Original Nuttah" by Shy FX & UK Apache.
The film had its world premiere at the Cannes Film Festival on 14 May 2009. Curzon Artificial Eye and IFC Films acquired United Kingdom and United States distribution rights to the film respectively. The film went onto screen at the Edinburgh International Film Festival, Karlovy Vary Film Festival, Telluride Film Festival, and the Toronto International Film Festival. The film was released in the United Kingdom on 11 September 2009. It was then released in the United States on 15 January 2010.
Rotten Tomatoes reports that 91% of critics reviewed the film positively, based on a sample of 141 reviews, with an average rating of 7.6 out of 10. The consensus states "Cannes Jury Prize-winner Fish Tank is gritty British realism at its very best, with flawless performances from newcomer Kate Jarvis, and Michael Fassbender." The New Yorker's David Denby writes, "Fish Tank may begin as a patch of lower-class chaos, but it turns into a commanding, emotionally satisfying movie, comparable to such youth-in-trouble classics as The 400 Blows".
Fish Tank was released domestically on 11 September 2009 taking £103,180 on its first weekend and a total of £332,488. As of 15 June 2010, the film earned $374,675 in the United States and $1,612,034 elsewhere, bringing the worldwide total to $1,986,709.
A new high-definition digital transfer of the film was released on DVD and Blu-ray by The Criterion Collection in February 2011. Extras include three short films by director Andrea Arnold: Milk (1998), Dog (2001), and the Oscar-winning Wasp (2003).