i think your tank is about an 8x2x2 (240g), which will be good for a couple years. the legth is good for a long time, but the width (and maybe the height) aren't enough for life.
I am 90% sure it is a Silver Arowana. It sounds like you have a 240 us gallon tank which is the minimum for a full grown Silver Arowana so you should be fine with that tank...
nope, its more than the standard 240, its 4 inches wider and taller, plus its a little longer than 8' I think that would land him about 300+ gallons. i'd say silver to. 1200-1300 litres?
good to see some europeans here dude! I have been to belguim 2 times to visit Graspop metal meeting! Great festival and most of all great people!