Thousands of fingerling salmon were released into Elliott Bay with the hope that they would return to the aquarium fish ladder to spawn. Inside the aquarium, visitors walked along ramps viewing sponges, jellyfish, snails, clams, and crabs, most of them native to Puget Sound. The glassed-in Aquarium Dome allowed visitors to sit on benches and watch fish watching them.
Sea otters performed tricks in return for horse clams, while an octopus clung to a pier. Many of the animals inhabited outside viewing areas in their natural habitat of Puget Sound, enabling visitors to watch sandpipers hunting for food and ducks nesting in grass.
Mayor Wes Uhlman said the aquarium and the crowd "expresses the relationship we in Seattle have with the sea." Former city parks director Dave Towne called the grand opening "the biggest new show in town."
King County voters approved construction of the aquarium as a part of the Forward Thrust proposals on February 13, 1968.