How Long Do Coelacanths Live? The Century-Old Fish

How did scientists work out a coelacanth’s age?

Like trees, many fish lay down growth rings. In fish they appear on the scales and on small ear bones called otoliths, and counting them is the standard way to age a fish. On the scales, the rings are tiny ridges called circuli.

Earlier studies had counted the visible rings on coelacanth scales and concluded that the fish lived no more than about 20 years. That made the coelacanth one of the fastest-growing fish in the sea, which never quite fit. Coelacanths have a slow metabolism, take up oxygen poorly, give birth to few young and live in cool, deep water, all signs of a slow-living animal.

In 2021, researchers from the French marine research institute IFREMER and the National Museum of Natural History in Paris examined the scales of 27 coelacanths under polarized light. They found much finer marks that had been invisible before, and tested whether these formed once a year. Their results showed that the maximum age had been underestimated by about five times.

What did the 2021 study find?

The scale study changed almost everything known about the coelacanth’s life history.

The oldest fish in the sample was estimated at 84 years old when it was caught in 1960. Scales from two unborn pups also showed growth marks, which helped the team estimate a pregnancy of around five years. If confirmed, that would be one of the longest pregnancies known in any animal, longer than that of the deep-sea frilled shark, estimated at about three and a half years.

These results matched what field researchers had seen. During 21 years of submersible dives off the Comoros, Hans Fricke’s team recognized individual coelacanths by their unique white spots and saw some of the same adults again and again for more than two decades. Based on their long-term observations, they had already suggested that coelacanths might live 100 years or more.

Why do coelacanths live so long?

Long life usually goes with a slow pace of life, and the coelacanth is one of the slowest fish known. It lives in cool water of about 14–22 °C (57–72 °F), spends the day resting in caves, and hunts at night by drifting with the currents rather than chasing prey. All of this keeps its energy use very low. According to the 2021 study, its growth is among the slowest of any fish of its size, comparable to deep-sea sharks with a similarly reduced metabolism.

Slow growth goes hand in hand with late breeding. A female must survive for decades before she can reproduce, and then carries a small litter of 5 to 26 pups through a very long pregnancy. Instead of producing millions of tiny eggs like a cod, the coelacanth puts its energy into a few large, well-developed young, each up to about 35 cm (14 in) long at birth.

How do coelacanths compare with other long-lived fish?

A lifespan of about 100 years puts the coelacanth among the longest-lived fish, though not at the very top.

The record holder, the Greenland shark, is covered in how long do Greenland sharks live?, and long-lived animals of all kinds are ranked in the longest-living animals.

Why does a slow life make coelacanths vulnerable?

A long, slow life is a weakness when people start removing animals. If a female needs 40 years or more to mature and then breeds only every few years, each adult lost by accident takes decades to replace. The West Indian Ocean coelacanth is already listed as Critically Endangered by the IUCN, and the population off the Comoros is thought to number only a few hundred adults.

The main danger is bycatch, the accidental capture of coelacanths by fishermen using deep lines for other fish or deep-set gillnets. The authors of the 2021 study concluded that, because the species lives so slowly, coelacanths may be even more threatened than previously thought.

How long does the Indonesian coelacanth live?

No one knows yet. The Indonesian coelacanth, Latimeria menadoensis, has been studied far less than its African relative, and its age and growth have not been measured with the new method. Because the two species are so similar in body, habitat and behavior, it is likely to be long-lived too, but that remains to be confirmed. The story of how both species were found is told in how was the coelacanth discovered?