That's a L-type show tank in a public aquarium (neoprodigy had been there during his trip to SE Asia). It's hard to estimate the tank size, it's simply huge enough. Those arapaima gathered around there is due to it's the feeding spot, and whenever people stand in front the window, the arapaimas think it's feeding time. That's awesome hearing them make subwoof type loud "bang" when getting their preys. Some of them are over 10ft (maybe 12ft). I have to say that public aquarium is not a great one (bad fish caring, etc.), but, that arapaima tank is worth to spend some time.