The show was called Nigel Marvens Piranha Adverture and was shown on Discovery several times. You can get it at Amazon.com I think.
You will see some good underwater shots. Mainly P's like to live close to tree roots for shelter but then often will venture out in packs, then they will be making their way round vegetation and rocks.
I personally have found P's in home aquaria get bored sometimes and rip your plants to bits, so I keep all my personal P's with large peices of bogwood and rocks.
Nickg