fish tank

just to mention an English language movie for a change, I saw Andrea Arnold's Fish Tank at our local picturehouse cinema last week and loved it. To save me the trouble of raving on about it, here is an excellent review by the Guardian's Peter Bradshaw, and I agree with everything he says.

Haven't figured out where the title comes from. If it's relating to anything in the film, I missed that bit. Does it refer to the bloke's fish catching technique ?