Demystifying the Coelacanth

Coelacanth in the ocean

A coelacanth (image: National Geographic)

A few days ago, Robin Stobbs (a frequent commenter on this blog) sent me an email in which he addresses some common misconceptions about the coelacanth. The coelacanth has been nicknamed the “living fossil” because until the discovery of live specimens it was only known through fossils.

I was always fascinated by this fish (although not nearly as fascinated as Robin who has spent more than 30 years of his career studying the coelacanth) but was not aware that it was the topic of more than a few bewildering myths and misconceptions. I found this extremely interesting, both because these fish are cool, and because I wasn’t aware of the pseudoscience and woo associated with them.

Robin was commenting on a coelacanth blog (extracts of which are in quotation blocks here):

In 1938 Majorie Courtenay-Latimer the first curator of the Natural History Museum in East London, South Africa, found amongst a ton and a half of a trawler catch a breathtaking blue coelacanth (pronounced “SEAL-a-canth).

Archival records in the library of SAIAB (ex JLB Smith Institute of Ichthyology in Grahamstown, South Africa) show quite clearly that the captain (Hendrik Goosen) and crew of the trawler ‘Nerine’ went to great lengths to preserve and set aside that coelacanth for Marjorie. The fact is the fish was not under a pile of trash fish. Nor was it blue when first seen by Marjorie C-L since like most blue-coloured fishes the colour fades very rapidly after death and that fish had been stone dead for many hours before it was brought into East London harbour.

Professor Smith waited until 1952, some 14 years after the first discovery before the next coelacanth was caught off the Comoro Islands, a remote volcanic archipelago at the head of the Mozambique Channel, halfway between Mozambique and Madagascar.

JLB (as he was known to family, friends and colleagues) was forced to wait out the war years following which he went to great lengths to distribute reward pamphlets along the East African coast. Meanwhile Comoran fishermen had been occasionally catching coelacanths unaware of their scientific value. So it was only the next known to science that was caught off Domoni in 1952!

Coelacanths are able to swim forward, backward, upside down and on their heads.

Like any other fish – especially those that propel themselves by using their paired fins rather than their tail and caudal fin!

Coelacanths live 400 meters beneath the surface. During the day they are inactive seeking protection in volcanic caves. At night these nocturnal predators are on the hunt. Their luminescent alien-green eyes have adapted to extremely low light levels – so much so that they do not hunt during a full moon.

An analysis of catch records from the Comoros (and recently updated by Rik Nulens[1]) show that coelacanths have been caught or observed from as shallow as 50 metres with unconfirmed sightings and a catch from less than 30 metres. Coelacanths living off Madagascar and the East African mainland coast do not have volcanic caves for refuge. Instead they seek shelter in overhands or shallow ledges.

Nobody has tested the low-light vision of Lartimeria and it is only presumed they have low light vision from the eye anatomy and eyeball size! My analysis of recorded catch dates compared to moon phase show that there is no correlation between the two – as many coelacanths have been caught off the Comoros during periods of full moon as there have during the new moon! There is, however a skewed idea resulting from the fact that the target species of Comoran fishermen is the oilfish, Ruvettus pretiosus, and this is primarily caught on nights when ambient light is of a low order.

The hollow spine of the coelacanth is composed mainly of a flexible cartilage – similar to a shark. Its spinal fluid is viscous golden and rumoured to act as an elixir. Coelacanths are thought to live for at least 40 years.

 

The coelacanth’s swim bladder is a slender oil-filled tube embedded in fat below the spine – it serves to increase its buoyancy.

The fluid contained within the ‘spinal cord’ is a low viscosity lipid, under slight pressure, and is similar to the lipids that fill every sinus and organ of the entire body. The swim bladder is fat-filled. Buoyancy is maintained by the entire lipid-filled body of the fish and so, like many sharks, the fish is capable of considerable vertical movement in the water column – there are no gas-filled sinuses that undergo compression or decompression!

The superstition about this fluid being sought after by Orientals because of some supposed elixir was started by some irresponsible reporting and an article in the Tropical Fish Hobbyist in the 1980s!

In 1987 a submersible located and filmed wild coelacanths off the Comoro Islands.

And since then coelacanths have been flmed or photographed in their habitat by divers and ROVs in Indonesia, Madagascar, South Africa and along the Tanzanian coast.

In 1998, Professor Mark Erdman, University of California Berkeley, discovered a new golden brown Indonesian coelacanth Latimeria menadoensis some 10,000 kilometers from the Comoro Islands in the Indian Ocean.

Actually the Indonesian coelacanth has the same colouration of the Indian Ocean ones – a clock spring steely blue with white to off white or pink blotches the pattern of which is characteristic of the individual (rather like a fingerprint).

Three hundred years before Agassiz found the first fossilized coelacanth, Mayan metallurgists were making exquisite miniature silver coelacanth jewelry [sic].

This has been shown to be false. The silver coelacanth votives were made by modern silversmiths – I don’t have the reference at hand but it was reported b Hans Fricke et al among others. There is nothing coelacanth-like in the little silver ornaments supposedly made by Mayans!

***

Thank you very much for taking the time to share your knowledge Robin.

***

[1] “An updated Inventory of all known specimens of the coelacanth, Latimeria spp.” Rik Nulens, Lucy Scott and Marc Herbin. Published as a Smithiana Special Publication by the South African Institute of Aquatic Biodiversity (SAIAB), 22nd September 2011

Image from National Geographic.

 

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One response to “Demystifying the Coelacanth

  1. 🙂 the coelacanth was the first exposure I had to dinosaurs and then evolution, I still remember my mom telling the story about its discovery to me as a little kid.

    Also, have the book by Smith in Afrikaans, “Ou Vierpoot”.

    funny when one thinks back to what triggered and pique some interests.

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