In many ways the reef can be compared to an urban zone. Not just a town, or even a substantial city, the reef is more like a major metropolitan center bustling with activity, day and night. During this time behaviors alter radically. Predation is at it's peak. As snorkelers, this is one of the very most exciting times to observe the reef community.
Visual ability is a fundamental survival skill among creatures of the reef, especially fish.
This is no easy task considering the highly competitive nature of reef life. By necessity, the eyes of fish are remarkably sophisticated. Many fish are also capable of binocular vision, allowing a keen sense of depth perception necessary for navigating the complex, three-dimensional coral world. Vision requires light, and we find that different species of fish have adapted successfully by evolving eyes that function best under specific lighting conditions. In general, fish that thrive in the abundant light of day, have eyes with small pupils facilitating excellent focus.