The story of the coelacanth, a fish that was thought to be extinct for millions of years and that we had been fishing all this time

That nature is amazing is a statement that should not come as a surprise to anyone. In the 4.5 billion years that the Earth has been around, humanity is only a second, but there are “animals” that appeared almost a billion years ago (according to recent records). Millennium after millennium, they evolved, but many fell by the wayside due to major natural disasters or simply because another species passed them by.

But every now and then, nature gives us a little surprise in the form of an animal that was thought to have been extinct for hundreds of millions of years, but which, by chance, is showing signs of life again. That is the story of the coelacanths, which are some very special fish.

Living fossilsThe planet is big. It’s another obvious fact, like the fact that nature is amazing, but it serves to talk about how, obviously, we can’t monitor everything. Without going any further, although we know the surface quite well, the oceans remain a mystery. And, sometimes, some species that had been missing for decades are “rediscovered.”

However, there is another interesting case: that of animals that have evolved very little, over hundreds of thousands of years. These are species that have undergone very few mutations in millions of years and which we call “living fossils”. They are usually fish and the protagonist of our story is one of them, which is famous not only for its “immutability”, but because for decades we thought it was extinct.

The coelacanth. The coelacanthiomorphs They are not as hideous as other living fossils. In fact, they could easily pass for a modern fish, but they have something special: they appeared in the Devonian period about 400 million years ago and many fossilized remains have been found dating back 350 million years. They belong to the Sarcopterygian family (this is important for something we will see later) and they were lobe-finned fish. In fact, they had many fins, with the lower ones having a remarkable length and consistency.

Based on the fossils found and the fact that we had never seen a coelacanth (or thought we had never seen one), the fish was classified as another of those species that had become extinct millions of years ago. Everything changed in 1938.

“A living fish from the Mesozoic,” said Nature in 1939

The event of the centuryOn December 22 of that year, South African fishermen caught a rare specimen using a trawling technique in a river at a depth of about 60 metres. It was 1.5 metres long and weighed about 50 kilos, so they must have been delighted. However, they did not keep it, because when it arrived at the port of East London, the curator of the East London Museum, Marjorie Courtenay-Latimer, realised that it was a special specimen. She could not identify it, so she stuffed it so that someone could investigate it in depth.

Not knowing what it was, Marjorie sought a more expert opinion from Professor JLB Smith. She sent him a series of notes and a sketch of the fish… and the surprise must have been huge: it was a coelacanth. The professor replied with a telegram: “It is very important to preserve the skeleton and gills.”

Surprise! Smith and Latimer maintained close contact, commenting The two men went through the various steps of the investigation by correspondence and came to a conclusion: “The fish resembles forms that have long since become extinct and must be of great scientific value.” It certainly was. As it had been discovered in the Chalumna River and the specimen had been sent to him by Latimer, he named it the Latimeria chalumnae. And that’s it.

Smith wanted to find another specimen and posted advertisements in several languages ​​on the coasts of south-east Africa, but it took 15 years until, in 1952, a merchant captain claimed to have information about a specimen captured in the Comoros Islands, some 2,500 kilometres from South Africa. Smith moved heaven and earth to get there as soon as possible and, after convincing the South African Prime Minister of the importance of the event, was able to fly to see the specimen thanks to the country’s air force.

If you see this fish, stop it!

More capturesWith that second specimen, Smith was able to carry out a more exhaustive analysis, but little by little other coelacanths began to appear. The National Geographic Society, with support from the German magazine Geo, financed an expedition that allowed the first underwater images of the coelacanth to be taken in its natural environment. This happened in 1987 and, over the years, we have seen more and more fish from this family.

And it turns out that they were not only in South Africa, since in 1998 another species was discovered: the Indonesian coelacanth or Latimeria menadoensisThese live in the Indian Ocean at great depths and this is curious, since they reflect an evolutionary divergence similar to that between humans and chimpanzees.

How does he come back to life? The answer to this is simple: it was never dead. At least, not completely. But… how did it survive for millions of years almost without variations? For this, there is a combination of four keys to the coelacanth:

• Their fins were adapted to maneuver at great depths in complex environments.
• The environment is stable, as they live in deep ocean caves that have not changed much over millions of years. It is an environment with few predators and no competition, so the coelacanth was not forced to evolve.
• Their metabolic rate is low, so they can survive in environments where food is scarce.
• Since its habitat has not undergone as many changes as those of shallower or surface areas, the fish simply did not feel the evolutionary pressure.

Sexual unknownsWe know that they live in areas between 150 and 300 metres deep and that they come up at night to hunt reef fish, but their reproduction remains a mystery. It is estimated that sexual maturity occurs at 20 years of age and they are ovoviviparous with eggs up to ten centimetres long. Gestation lasts a year and the offspring are perfectly capable of surviving on their own, so there is no parental care. However, we do not know what their reproductive behaviour is.

Photo by Chris Bloom

Another missing link? Beyond its physiognomy, the coelacanth is a very special fish. esteem They can live up to 100 years, and in fact, a specimen was captured in 1960 that was about 84 years old. It is estimated that they reach maturity at 55 years of age, a conclusion we reached based on the analysis of the growth marks on their scales.

Remember when I mentioned that fins were important? Aside from all this and the scientific milestone of discovering that they were still alive, sarcopterygians are considered to be the most tetrapod-like fish, and they are the fish that initiated the transition from marine life to terrestrial life. The first to colonize the surface, that is. This is estimated to have occurred in the Devonian thanks to the development of limbs in marine creatures, something that coelacanths possess.

However, despite such powerful fins, the closest relative of tetrapods are the lungfishwhich is a distant cousin of the coelacanth in another branch of the sarcopterygians.

Image | Chris Bloom

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