piranha behavior

[John Rambo]

Does any one know why, at times, a shoal swims randomly in different individual directions, and other times, all point in the same direction and gouped together?

Does this have to do with water current, quality, hunger, being full?

 

[pyromaniac]

i think in the normal resting state the fish just hang around in a loose shoal and stay in one spot,with the ocassional arguement with one another quickly settled by fin flaring and posturing
if frightened,the whole shoal swim away together as a tight group
and when feeding or hungry they swim all over the tank like ,say a group of livebearers,just milling around ready to pounce on anything eatable. and of course while attacking bigger objects they do so as a group.
i just love the the lazy elegance of a group just hanging around in the current waiting for something to happen.