Peter Ericson’s review published on Letterboxd :
Raw authenticity. Those are the words I would use if I were to describe "Fish Tank" in only two words. Sure, there are moments when the stark social realism takes on a kind of dream-like, almost poetic quality, but the picture is still defined by its realism.
Writer/director Andrea Arnold skillfully weaves an engrossing and unpredictable narrative that effectively holds the viewer’s attention in a vice-like grip from beginning to end. Things are constantly bubbling beneath the surface, and situations of pulse-pounding intensity occasionally arise over the course of the movie’s 123-minute running time. The stylistic choice to shoot "Fish Tank" in an aspect ratio of 1.33:1 gives the film an appropriately claustrophobic feel.
Katie Jarvis, who plays Mia, delivers a marvelous performance that is made even more impressive by the fact that she has no previous acting experience (she was discovered while having an argument with her boyfriend); Mia may not be a particularly likable person, but one nevertheless wants to find out what is going to happen to her next. Kierston Wareing and Michael Fassbender are remarkably good in the roles of Joanne, Mia’s mother, and Connor, Joanne’s latest boyfriend, respectively. Rebecca Griffiths, who is a natural as Tyler, Mia’s younger sister, provides some restrained comic relief and also shares a genuinely touching scene with Jarvis at the end of the film.