Coelacanth specimen

Deep dive

Scientists just discovered this "living fossil" has an incredible lifespan

This long-lived fish may just outlive you.

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A shadowy figure lurks beneath the blue ocean pixels in Animal Crossing: New Horizons. Your avatar throws out their fishing rod — hoping to snag the beast — but after a brief tug, it swims out of their grasp.

Like Ahab and his whale, catching the coelacanth is a difficult task in the world of Nintendo — the elusive fish is one of the rarest in the game. The nature of this big, ancient fish has often eluded real-world scientists too: Thought to have gone extinct 65 million years ago, it was rediscovered in 1938 off the coast of South Africa. Today, it’s debatably a “living fossil,” straddling the line between ancient relic and enduring animal.

According to new research published Thursday in the journal Current Biology, the coelacanth is not only alive — albeit, endangered — but it may live longer than the average human, rewriting the evolutionary history of this enigmatic fish.

“We were quite taken aback!” co-author Marc Herbin, a senior lecturer at the National Museum of Natural History in Paris, tells Inverse.

A coelacanth embryo with a yolk sac attached. Researchers have discovered that the deep-sea fish can live for roughly a century.MNHN

What’s new — Using new age-dating technology, scientists have discovered that the coelacanth may live for nearly a century: Their oldest specimen was 84 years old. Previous estimates put the average lifespan of a coelacanth at 48 to 60 years old.

This makes the 6.5-foot long coelacanth one of the “most long-lived fish species,” the study reports.

The researchers gathered other surprising information about the animal’s life history, including its:

  • Late sexual maturity: 40 to 69 years old for males and 58 to 66 years old for females
  • Long gestation period: female coelacanths can only reproduce every five years
  • Slow body growth relative to its massive size (the fish can weigh up to 231 pounds)

These findings reveal the deep-sea creature’s unusually slow aging process and new information about the overall population of the fish.

“The turn-over rate of the population is very low, even lower than previously thought,” Herbin says.

A figure from the study comparing the new methods researchers used — in red — to older methods, allowing them to calculate the true age of the coelacanth.Couette, UMR CNRS

How they did it — The scientists used an entirely new method to reveal the true age of the coelacanth.

The last time researchers officially investigated the direct age of the coelacanth was in a 1977 French study: While scientists have thought these fish could live to 60, that’s more of an estimate than an official data point.

The 1977 study estimated the age of the fish based on concentric circle markings — known as macro-circuli — on its scales. These are visible using a light microscope. Using this previous methodology, scientists could only reasonably estimate coelacanths lived for up to 17 years.

The scientists in this study used polarized light microscopy to analyze the scales of 27 coelacanths captured off the coast of the Comoros Islands between 1953 and 1991.

Polarized light allowed the scientists to analyze the scales in much greater detail, revealing “new circuli that were thinner and more numerous” than previously found, the researchers write.

The researchers counted these smaller circuli in the same way that the 1977 researchers had, confirming that the marks grow annually. This informed the coelacanth’s updated age and likely lifespan.

“We showed that micro-circuli are formed annually and thus can be used to estimate the age of coelacanth,” Herbin says.

The team also compared the body growth of coelacanths to other marine animals using their new scientific methods, finding that the coelacanth is one of the slowest-growing fish and ages in a similar fashion to deep-sea sharks.

A close-up of the scales of a coelacanth, which researchers used to estimate its age. Laurent Ballesta

Why it matters — These findings reveal the powerful potential of new technology to rewrite the evolution of marine life.

The study also supports a scientific argument known as the “life history theory.” This proposes that delayed sexual maturation is one evolutionary tactic that can increase the chance of survival. The coelacanth may have fewer offspring than, say, a mouse, but it’s banking on the fact that its offspring will have high survival rates.

But because of their unusual aging process, the coelacanth has a smaller population size, making it vulnerable to disturbances such as “extreme climate events or accidental fishing” according to Herbin.

The IUCN Red List currently lists the African coelacanth as an endangered species. These new findings lend greater urgency to conservation efforts to protect the coelacanth. The researchers write:

“Our results suggest that [the coelacanth] may be even more threatened than expected due to its peculiar life history.”

What’s next — Despite the scientists’ remarkable discovery, there’s still much we don’t know about this enigmatic big fish. For example, researchers still don’t know how they hunt for food or where they reproduce.

“Many many things are still unknown [about] this animal, especially its behavior,” Herbin says.

However, with this new information on coelacanth aging, scientists are a bit less in the dark about this cave-dwelling, deep-sea fish — an easier find in Animal Crossing than in the real world.

Abstract: The extant coelacanth was discovered in 1938;1 its biology and ecology remain poorly known due to the low number of specimens collected. Only two previous studies have attempted to determine its age and growth. They suggested a maximum lifespan of 20 years, placing the coelacanth among the fastest-growing marine fish. These findings are at odds with the coelacanth’s other known biological features including low oxygen-extraction capacity, slow metabolism, ovoviviparity, and low fecundity, typical of fish with slow life histories and slow growth. In this study, we use polarized light microscopy to study growth on scales based on a large sample of 27 specimens. Our results demonstrate for the first time nearly imperceptible annual calcified structures (circuli) on the scales and show that maximal age of the coelacanth was underestimated by a factor of 5. Our validation method suggests that circuli are indeed annual, thus supporting that the coelacanth is among the longest-living fish species, its lifespan being probably around 100 years. Like deep-sea sharks with a reduced metabolism, the coelacanth has among the slowest growth for its size. Further reappraisalsof age at first sexual maturity (in the range 40 to 69 years old) and gestation duration (of around 5 years) show that the living coelacanth has one of the slowest life histories of all marine fish and possibly the longest gestation. As long-lived species with slow life histories are extremely vulnerable to natural and anthropogenic perturbations, our results suggest that coelacanths may be more threatened than previously considered.
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