Here are some examples of things I like to see when I go to a museum.
This is another photo taken at the Mystic Aquarium. It's an exhibit that shows how Flounder protect themselves from predators by blending into their environment. It's hard to tell from this photo because they are camouflaged so well, but there is a Flounder on the black gravel and a Flounder on the white gravel. What I like about this simple display is that it clearly conveys the message without the need for lengthy text panels or diagrams. A child who can't read yet or someone who doesn't speak the language will understand without having someone explain it to them. The exhibit teaches the lesson without the need for interpretive graphics.
AND just for fun, here are some images of things I think every good aquarium should have...