Marine Biology

What is a Coelacanth



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The name coelacanth is used to describe an order of fish that were highly successful, and common in the fossil record from the Devonian period, approximately 400 million years ago, up until the Cretaceous period, which ended 65 million years ago. Their  fins were attached to their  bodies by bony 'lobes'. Arranged in pairs like the limbs of terrestrial animals, many scientists believe these fish to an intermediate in the evolutionary line that led to the developement of amphibians, and hence other four-footed land animals. The order was believed to have died out by the end of the Cretaceous.

Then, in 1938, a discovery was made aboard a South African fishing trawler. Back from a fishing trip in the Indian Ocean, a large strange fish was amongst the catch. A young museum curator, Marjorie Courtenay-Latimer, recognised it as an important discovery, but could not identify the fish. Contacting the ichthyologist J.L.B. Smith of Rhodes University, the specimen was at once recognised as a coelacanth, a fish thought to have been extinct for 65 million years! Smith named the fish Latimeria chalumnae, in honour of Marjorie, and after the Chalumna river, near whose mouth the fish was caught. Although not commemorated in the name of the fish, the captain of the trawler was Hendrik Goosen.

Smith began searching for other specimens, and 14 years after the first, another fish was caught near to the Comoros Islands. Since then more specimens of  Latimeria chalumnae have been caught near the Comoros and off the eastern seaboard of Africa. In 1998, a second species of coelacanth was discovered, this time in Indonesia. Caught near Sulawesi, this fish was named Latimeria menadoensis.

The ceolacanth displays many traits not found in modern fish. It has the thick bony scales found only in prehistoric, extinct fish. It has an unusual tail, which is divided by a bony lobe at the tip, and as stated before, all the fins are supported by more bony lobes. A unique hinged joint in the skull allows the coelacanth to swallow larger prey, and it does not have a true backbone. Instead, an oil-filled notochord serves this purpose, a design still found in other primitive fish-like animals, such as the  lancelet. The brain is tiny, occupying only 1.5% of the skull cavity, the rest of which is filled with fat. An electrosensory organ in the snout helps to detect prey.

Modern coelacanths can live for up to 60 years, and can grow up to 6ft in length, weighing in at up to 90 kg. They live in groups at depths of over 100m, inhabiting caves by day and coming out to feed at night, and can be found in waters far deeper, up to 700m deep.  The females produce eggs which are fertilised within the body, and hatch there too. Only up to 5 young fish are then born when ready, and this may be one of the reasons their numbers are scarce. They are elusive fish, seldom venturing near the surface, and the number of Latimeria chalumnae is only thought to be near a thousand. Even less is known of the Indonesian species, and both species are considered endangered. Of no value as a food fish, they are, however, sought by unscrupulous collectors. An order of fish once thought to be extinct, and known as 'living fossils', is again in danger of dying out, and this time it will be for good.

This article was written with reference to the website of the Natural History Museum, London, and also the website of National Geographic, and coelacanth pictures can be found on both.

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