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Meet Methuselah - the oldest aquarium-based fish in the world.

The four-foot-long lungfish is believed to be 90-years-old and weighs 18 kilograms, which is equivalent to about 18 bags of sugar.

Biologists at the California Academy of Sciences said Methuselah, was brought to the San Francisco museum in 1938 from Australia.

According to the aquarium's workers, she likes to eat fresh figs, get belly rubs but can be a "little picky" with her food.

The Australian lungfish is a threatened species but the museum has two others which are younger and believed to be in their 40s.

It's known as a primitive species. This means it remains very similar to its ancestors in terms of appearance.

Methuselah is named after a Biblical figure, Noah's grandfather, who was said to have lived to be 969-years-old.

The previous oldest Australian lungfish lived at the Shedd Aquarium in Chicago - but died in 2017 at the age of 95.

Scientists think Methuselah is female but they aren't 100% sure so they're planning to send a tiny sample of her fin to researchers in Australia, who will try to confirm the sex and work out the fish's exact age.

Allan Jan, senior biologist at the California Academy of Sciences, is the fish's keeper.

"I tell my volunteers, pretend she's an underwater puppy, very mellow, gentle, but of course if she gets spooked she will have sudden bouts of energy," he said.

"But for the most part she's just calm. We just give her the best possible care we can provide, and hopefully she thrives."

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