I'm not an enormous fish person (to my marine-bio-studying father's everlasting shame and disapproval), but my take is that, with the exception of a few flagship species like sharks and seahorses, most people view tanks in aquariums like they would view gardens. They aren't really seeing the individual animals as much as they are all of the fish, at once, in one collective impression of color and motion (I think this is how many zoo visitors view mixed-species aviaries as well). Similarly, many folks who are not botanically-inclined will appreciate the holistic beauty of a garden without really stopping to observe and notice the individual flowers and plants. This is probably in part because most tanks in aquariums have so many species in them that it's harder for a visitor to really focus on one individual or species unless it truly stands out to them through size, shape, color, or activity. Instead, they process it as a coral reef, or a kelp forest, or a mangrove. Zoo exhibits for mammals, on the other hand, tend to be much more clearly focused on showing off individual specimens. The average visitor goes to the zoo and sees a lion. They go to the aquarium and they see a coral reef tank.