I agree that a 26g is wrong, a 55g is still no good, and a 90g might not be the best, but i dont think fish really get unhappy. if i actually got an aro for a 90g(which i wont because already have fish in it and would only do it if it was alone or with small catfish on the bottom), then in 2-3 years if i decided it was too cramped id give it away, but it seems like for a while it will be fine. i recently gave away my spotted gar because my tank is only 18" wide and he was 14", and though he seemed perfectly happy(hed come up to my fingers and rub his nose on them) i knew after a bit he couldnt turn because hes not flexible like the aro and my oscar would always take food out of his mouth and it wasnt fair to him. from watching them in the store, aros seem like they can turn in real tight spaces. the gar seemed content just floating against the current. the only fish ive ever seen get sad is my red oscar, who when he gets into fights with the albino and gets bullied sometimes gets and sulks at the bottom, but he always gets over it.