(CN) --- New research about the giant, primitive coelacanth proves that these gigantic fish, previously believed to be extinct, are not only still around, but actually have a lifespan that far surpasses what anyone had predicted.
In a study published Thursday in the journal Current Biology, researchers from the French Research Institute for Exploitation of the Sea examined 27 specimens of coelacanths, the living fossils who outlived the dinosaurs, and found that they can live up to a century old --- five times the age that researchers had once believed.
Coelacanths are an ancient species of fish that swam alongside the dinosaurs, and for a long time were thought to have gone extinct with them 65 million years ago. It wasn’t until 1938 when a museum curator from South Africa happened upon this underwater giant and shocked the world with photographic evidence of its existence. Several more have been discovered since then, including a subgroup in the waters of Indonesia.
These unusual fish are nocturnal predators, can reach up to 6.5 feet long and weigh almost 200 pounds. Because of their four lobed-fins, they are believed to represent a step in the process of animals evolving to walk on all fours on land. They also have an incredibly unique hinged joint in their skulls that allow them to open their mouths wider, another trait exhibited by early organisms transitioning from aquatic to land.
The team set out to discover the aging process of coelacanths after feeling skepticism about previous studies estimating their lifespans. These fish have very unique, thick scales called cosmoid scales, which are very hard and abrasive like armor. These earlier studies sought to analyze growth rings on the scales from 12 specimens, which resulted in a life expectancy prediction of 20 years.
This felt like a peculiar approximation considering the coelacanths’ physical traits, since a lifespan of 20 years would make it the fastest growing fish of its kind. Knowing that other similar sized, deep-sea species live much slower than that, the researchers sought to try a different approach.
"Our most important finding is that the coelacanth's age was underestimated by a factor of five," says Kélig Mahé of IFREMER Channel and North Sea Fisheries Research Unit in Boulogne-sur-mer, France. "Our new age estimation allowed us to re-appraise the coelacanth's body growth, which happens to be one of the slowest among marine fish of similar size, as well as other life-history traits, showing that the coelacanth's life history is actually one of the slowest of all fish."
In order to develop their own lifespan estimation, Mahé and her co-authors Bruno Ernande and Marc Herbin obtained specimens from the French National Museum of Natural History (Muséum National d'Histoire Naturelle de Paris, MNHN), home to one of the most impressive collections of coelacanths from all different stages of life. They created an entirely new estimation process involving the use of polarized light microscopy and scale interpretation technology at IFREMER's Sclerochronology Centre.
Using their state-of-the-art technology, they were able to study the coelacanth scales in immaculate detail, observing even the smallest traces of circuli, or growth rings, that the previous studies could have missed. They found that the lifespan of these prehistoric fish had been vastly underestimated, and they were actually five times older than earlier predictions.
"We demonstrated that these circuli were actually annual growth marks, whereas the previously observed macro-circuli were not," Mahé says. "It meant that the maximum longevity of coelacanth was five times longer than previously thought, hence around a century."
Additionally, after analyzing the coelacanth embryos housed by the museum with their new technique, the authors found that they were about five years old, meaning that the average gestation period for these fish was a surprising five years long.
"Coelacanth appears to have one of, if not the slowest life histories among marine fish, and close to those of deep-sea sharks and roughies," Mahé said.
The team is hopeful that their research will contribute to the study and conservation of coelacanths, including the African coelacanth which is currently listed as critically endangered in the Red List of Threatened Species of IUCN. They believe the next step in their studies will be to test the effects of global warming on the coelacanth scales to see if temperature will impact their growth.
"Long-lived species characterized by slow life history and relatively low fecundity are known to be extremely vulnerable to perturbations of a natural or anthropic nature due to their very low replacement rate," Mahé said. "Our results thus suggest that it may be even more threatened than expected due to its peculiar life history. Consequently, these new pieces of information on coelacanths' biology and life history are essential to the conservation and management of this species."
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