The coelacanth is an ancient type of fish that may grow up to 6.5 feet long and can be found off the beaches of East Africa and Indonesia. They live in the ocean’s “twilight zone,” which is 500 to 800 feet below the surface and is faintly lighted. Little is known about these sluggish behemoths. Experts originally believed they died out with the dinosaurs 65 million years ago. Scientists didn’t understand the marine mammoths were still swimming in the deep until the first living specimen was caught in 1938.
Because of their unusual behavior—they spend most of the day huddled together in volcanic caves—scientists have only seen a few coelacanths. Because the creatures are designated as severely endangered, fishing them is illegal, and only a small percentage of them ever make it to the surface. However, research published in Current Biology this month has begun to reveal some of the secrets of these scaly creatures.
The most recent study, which was not sponsored, discovered that coelacanths live five times longer than previously thought. Before this study, marine ecologists thought the behemoths lived to reach 20 years old, making them one of the most rapidly growing aquatic species. Ecologists now believe they may live to be 100 years old, a highly uncommon feat.
A long lifespan isn’t surprising to biologists who are familiar with the strange species. Slow metabolism, poor oxygen extraction capacity, tiny batch production, and ovoviviparity, or when a mother carries eggs within her body until they are ready to hatch, are all signs of a long-lived, slow-growing organism.
According to Bruno Ernande, a marine ecologist at the French Marine Institute and co-author of the study, “that exceptionally high development rate was originally thought to be extremely unusual compared to other characteristics [of coelacanths].” “It didn’t fit the picture at all. As a result, we decided to look at the age range of coelacanths again.”
Getting to the bottom of hidden growth rings
Scientists count growth rings on a fish’s scales to determine its age, similar to how tree trunk rings are counted. Each ring represents a year in one’s life.
Previous research has used reflected light, such as that found in a flashlight, to observe these growing rings. Ernande and his colleagues, on the other hand, used polarised light, a more recent technology that accentuates the contrast between the rings.
The researchers looked at 27 preserved specimens of various ages and genders in total. Embryos were the youngest, and the oldest was 84 years old.
“What we discovered when we employed this novel technique was that there were practically undetectable rings that went missed before,” Ernande explains. He and his crew discovered five faint rings for each larger, thicker ring. “So, basically, this is how we concluded that the age of coelacanths was five times underestimated.”
Coelacanths can live to be 100 years old, and they don’t attain sexual maturity until they’re in their forties or sixties. The aquatic giants not only live long lives, but they also have a 5-year gestation period, which is possibly the longest of any marine fish and a good deal longer than most mammals.
Every fifth year, coelacanth specimens deposit bold bands, according to Ernande’s team. They know it’s not due to environmental conditions because the ribbons weren’t homogeneous between species, but it could be related to reproduction cycles that last five years. However, he emphasizes that this is all speculation.
Why isn’t age merely a number?
Coelacanths are threatened by fishing, channel dredging, submarine blasting, and deep-water port building, all of which have classified the creatures as endangered and jeopardized their 360-million-year existence on the earth.
Furthermore, animals with a sluggish reproduction rate, such as coelacanths and the great ape, are especially vulnerable to environmental or human-caused changes. While some fish may carry over a million eggs per gestation, coelacanths only carry roughly 20, according to Ernande, due to their sluggish maturation and gestation.
“Any human-caused or unintentional death takes a long time to replace,” Ernande explains.
Understanding the true life span of these living fossils is critical for determining the species’ demography, which can then be used to inform conservation policy.
“There is still a lot to learn about this species,” Ernande explains.
Grace Wade is a contributor and associate editor on Insider’s health reference team.
