On Feb. 5, 2017, a fish at Chicago’s Shedd Aquarium passed away. But fish die every day. It’s the circle of life, and no one truly mourns for one little fish. As the saying goes, there are plenty of fish in the sea.

But what about a fish that has both lungs and gills? What about a fish that can live longer than some humans? What about a fish that over 104 million people have seen? This is where Granddad’s story begins.

In 1933, an Australian Lungfish, also known as a Queensland Lungfish, was brought to Shedd Aquarium. In an effort to attract more visitors, it went on public display during Chicago’s Century of Progress World’s Fair. Given the name “Granddad”, what began as an intriguing new exhibit became an extraordinary feat of nature. In fact, according to the aquarium, Granddad was the oldest living aquatic animal in any public aquarium across the world.

After 84 years of residency, the Animal Health team made the tough decision to euthanize Granddad on Feb. 5 due to rapid health failure.

Australian Lungfish are an endangered species that live in a very small habitat. There are only a few rivers and reservoirs on the eastern coast of Australia that provide the right environment for the species. With a lifespan of 50-100 years, the organisms have existed for over 100 million years. They spend the majority of their time laying on the river bottom but swim occasionally to gather food. Billie Mcfarlan, a volunteer at Shedd Aquarium for two and a half years, is amazed by their existence.

“They call them ‘sleepy fish’, but there’s so much more to them,” said Mcfarlan.

The most interesting fact about these fish is their respiratory system: they have both lungs and gills. Though they generally obtain oxygen from water, they have the ability to swim to the surface and gulp air in case of an absence of waterborne oxygen.

Adult lungfish have few to no natural predators, leaving many to wonder the cause of their population decrease. However, the answer is simple: dams. Upstream, dams block lungfish from swimming to the proper breeding site. Downstream, more sediment decreases water quality and causes bank erosion, severely diminishing the lungfish habitat. Due to the small area where they spawn, habitat is an essential factor to keep this species alive.

Although Australian lungfish may spend most of their day sitting on the bottom of the river, they have a purpose in our world. Not only do they control the small fish population, but they provide an example of nature defying its own laws. It’s not common that generation after generation can visit the same fish, one that existed when photographs were still black and white.

“They’re prehistoric, and every day we’re finding out more and more about them,” Mcfarlan said.

To learn more about Granddad’s story, visit the Shedd Aquarium’s tribute. To learn more about the species, visit the Australian Government’s Department of the Environment and Energy.