‘Living fossils’ are also the fiercest of the seas, a study reveals: Hollow fossils can live nearly a century, and therefore live five times longer than previously thought. The life hours of these animals swing very slowly, according to studies: the acidity of the hollow reaches sexual maturity only at the age of more than 40 years, and the gestation period of live fish lasts five years, researchers report.
Due to the amazing discovery history, the coelacanth has become an icon of evolutionary biology. Initially, this bony fish with its grotesquely leg-like fins was known only from fossils up to 400 million years old. It was assumed that the relatives of these creatures belonged to the ancestors of terrestrial vertebrates. In 1938 a sensation followed: a fish resembling a fossil coelacanth was caught off the African coast. In fact, the species called Latimeria chalumnae turned out to be a living representative of this ancient family. It is clear that this fish has not changed its ancient appearance over the course of millions of years. Presumably, this was not necessary in its habitat: excavations showed that gophers, up to 2 meters in length and weighing more than 100 kilograms, live in caves at a depth of 150 to 400 meters.
Age is underestimated
Since then, the coelacanth of the Comoros has been intensively studied. Researchers have already investigated the question of the age of these fish. The evaluations were based on examination of visible growth rings (macrocirculi) on scales of twelve samples. The results led to the assumption that the fish did not live for more than 20 years. According to this, however, they will have to reach their large size relatively quickly. This seemed surprising, because other biological and ecological characteristics of coelacanths seemed more common to fish with slow development. For this reason, researchers on Kélig Mahé from the Fisheries Laboratory of the IFREMER Marine Research Institute in Boulogne-sur-Mer conducted a new study of the life expectancy and growth processes of the notable fish.
They were able to access sample materials from the French National Museum of Natural History in Paris. It houses the largest group of coelacanths in the world, ranging from fish embryos to individuals approximately two meters long. In total, scientists examined material from 27 samples. In contrast to previous studies, Mahi and his colleagues used modern methods to analyze the exact structures of scales – the so-called circles.
“We were able to show that these circles are in fact signs of annual growth, whereas the larger circles observed previously were not,” Mahi says. Specifically, investigations have now shown that the oldest specimen in the sample is 84 years old. “This means that the maximum lifespan of the hollow is five times longer than previously assumed – probably about a century.” This results in a new assessment of the coelacanth’s body growth, as the scientist says: “It is thus one of the slowest growing marine fish of this size,” Mahi says.
Five years of pregnancy
Other findings fit this picture as well: Colas have not been shown to be sexually mature until they are 40 to 69 years old. In addition, the researchers revealed details of an interesting property of coelacanths: their plasticity. The study now shows that the young animals are carried in the womb for a surprisingly long time: Examination of two coelacanth embryos showed that both were about five years old. It seemed that they were about to give birth, as evidenced by their size. “Geomorphs seem to have one of, if not the slowest, life history among marine fish,” Mahi says.
As scientists finally confirmed, the findings also have an impact on protecting rare cave dwellers. “Long-lived species, which have a slow life history and relatively low fecundity, are known to be highly susceptible to natural or human-induced disturbances,” Mahi says. “Our results indicate that coelacanths in Comoros, due to their special way of life, can be more threatened than previously assumed. Therefore, this new information about their biology is of great importance in the conservation and management of this species,” said the scientist.
Source: Cell Press, technical article: Current Biology, doi: 10.1016/j.cub.2021.05.054