The giant coelacanths, a kind of fish considered extinct by marine biology, there are still individuals swimming in the depths of the ocean. The species, which has a few hundred millions of years, lives in a deep and complex habitat to study. But new research may show that they live much longer than marine life experts believed until now.

Until now, it was thought that these fish lived for about 20 years, however, this new study shows that each individual can easily reach a century of life. If confirmed, it would make African coelacanths one of the slowest-growing fish in the oceans, along with deep-sea sharks.

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hard to study

As a marine animal that lives in the depths of the ocean, coelacanths have some characteristics that are common in animals that live in this type of habitat, such as a slow metabolism and low fecundity. In addition, they take time to age and also to reproduce, which is something already known about these creatures, who live in one of the quietest places at the bottom of the oceans.

“Our new age estimate allowed us to reassess the body growth of coelacanth, which happens to be one of the slowest among marine fish of similar size,” said Kélig Mahé, marine biologist at the Ifremer Institute in France, to the Science Alert.

Calcified structures in the scales can help measure the age of coelacanths. Credit: Laurent Ballesta/Science Alert

He and his team studied the largest group of coelacanths ever collected, with 27 individuals of varying age, one of them with an estimated age of 84 years. According to them, these fish reach maturity at around 55 years of age and each gestation lasts around five years.

The researchers also found very small calcified structures, known as circuli, in the scales of coelacanths. These structures can be used to measure the aging of these fish, similar to the way we use the rings on the trunk of a tree to know its age. This was the first time that these markings were located in this species and, according to experts, they really correspond to the age of growth of the fish.

not so lonely

“We demonstrated that these circulations were, in fact, annual growth marks, as opposed to the macrocirculations observed previously,” said Mahé . “This meant that the maximum longevity of coelacanth was five times longer than previously thought, therefore, about a century”, added the biologist.

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Capable of reaching up to two meters in length, coelacanth can be considered a “living fossil”, since species with close relationships to it have already been extinct. However, recent research shows that this fish may be less alone than imagined in its evolutionary tree. A study earlier this year revealed that this fish has been borrowing genes from other underwater species over the years, in a process known as horizontal gene transfer.

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