Not only is the coelacanth one of the world's oldest fish species, but the individual fish may also be long-lived.

A new study suggests the ancient fish can live up to a hundred years and even longer.

Until 1938, when a coelacanth (pronounced SEE-la-kanth) was found off Africa's coast, scientists had believed the fish went extinct 65 million years ago with a related lineage of prehistoric fishes. (See more coelacanth pictures.)

After the coelacanth's rediscovery, a number of populations were uncovered in parts of the western Indian Ocean and in the western Pacific Ocean. Whether these populations were interconnected was a mystery.

"People kept catching these fish, but that didn't tell us anything about their population, how numerous they were, or if they were maybe simply strays from different parts of the ocean," said study leader Hans Fricke, an ethologist—or expert in animal behavior—formerly of the Max Planck Institute in Bremen, Germany.

Coelacanths Studied via Submersible

This lack of reliable data led Fricke and colleagues to begin a 21-year study of a coelacanth population found near the Comoros, a group of islands between the Seychelles and Madagascar.

Because the fish live at depths of about 525 to 650 feet (160 to 200 meters), sending divers down to observe the fish was out of the question.

Instead, the team used submersibles to photograph, videotape, and study the fish. Because coelacanths have unique white markings on their sides, the team was able to identify more than 140 individuals during hundreds of submersible trips.

But the team couldn't find any youngsters in the population of 300 to 400 coelacanths.

There's also little known about how the fish are born, noted Fricke, whose study appeared recently in the journal Marine Biology.

"We darted a pregnant female with a pinger [a type of tracking device] and followed her descent into the deep, so we think mothers may be going to great depths to give birth," he speculated.

Even stranger, only three or four coelacanths seemed to die each year, and their places in the population were taken by three or four new adults that would just mysteriously show up from nowhere.

Because roughly 4.4 percent of a given population of coelacanths appear to die each year—a figure at the lower end of observed mortality rates among fish—Fricke estimated that coelacanths have a longevity of about 103. Other fish, such as deepwater rockfishes of the genus Sebastes, have similar death rates and live for about a hundred years.

With so few deaths and so few replacements in the population, Fricke argues that the evidence is clear that these fish are very long-lived.

Youthful-Looking Fish Hard to Age

Even so, the fish don't show the ravages of time, which makes determining their age very hard.

What's more, normal methods for measuring fish ages, such as measuring growth rings on their scales, aren't possible with coelacanths. That's because coelacanth scales don't seem to change over time like other fish, Fricke said.