Sufficient size of the tank is one of the most important things every fish keeper should be aware of, absolutely. I would never put any fish into a small tank - this is what I hate so much about dolphinariums. Btw I am actually more into keeping crustaceans - crayfish and crabs - than fish ;) But like I said - even though I am quite confident I always took the best possible care of every single creature living in my tank, I am more and more questioning the moral of this hobby. I actually haven´t had a fish tank for years already as it is simply not compatible with our current nomadic lifestyle but I might well end up giving up on this hobby even once we settle down, just because of the ethical aspect of it.