The oldest aquarium fish in the world is at least 90. She lives in San Francisco.

In 1938, Methuselah arrived in San Francisco on a boat from Queensland, Australia and took up residence at the Steinhart Aquarium. Methuselah is a lungfish who, at around 90-years-old, is thought to be the world's oldest fish living in a zoological setting. She took the spot as eldest when Granddad, a lungfish who lived at Chicago's Shedd Aquarium, died in 2017 at 84. The San Francisco Chronicle profiled Methuselah and her best friend, California Academy of Sciences biologist Allan Jan. From the SF Chronicle:

Methuselah is also unique for several high-maintenance quirks, which have caused alarm — and comedy — at the aquarium.

"Sometimes she'll just start floating, tail up," Jan explains. "And then we'll get a bunch of calls. 'What's wrong with the fish? What's wrong with the fish!' … To the public, it looks like she's in distress."[…]

Jan says he works on "enrichments," which include training and tactile interactions, where he touches the fish to give them comfort and make them more acclimated for inevitable weighings and medical procedures. Asked what types of tactiles Methuselah enjoys, he says "literally belly rubs."