perhaps this wasn't how you intended it to come across, but this is the same argument that herptile keepers use to justify sticking snakes in tiny containers. Octopuses do like an enclosed space for security, but not as their total living area -- in other words, they like to hide in tight spots but when they are active they are very active and need lots of room, quite apart for the amount of attention required to keeping their minds occupied (they get bored of play-things very quickly, so always need novel items to entertain themselves; much like apes really - except apes don't tend to gnaw off their own arms!). The problem for public aquariums is that most octopuses are nocturnal and so a large complex tank appears to be empty most of the time.chrisbarela said:
chrisbarela has some good ideas in post #5 and also the basic reason why it doesn't happen ("the response has always been the cost won't equal the amount of use."). For a good octopus tank I'd imagine a proper rocky reef with lots of nooks where food is randomly hidden so the octopus has to actually search it out, a good comparison might be scatter-feeding for gorillas. If you've ever seen footage of them in the wild they are very active, and continually exploring their environment. In general octopuses eat hard-shelled animals (crustaceans, shellfish, etc) and ignore soft-bodied animals like starfish and sea cucumbers, so you could design it as a living reef if care was taken in choosing the inhabitants (but no fish because octopuses love fish, and some fish love octopusesDavidBrown said:
). There could be dens with openings visible to the public so they can still see it when its asleep.