adminA coelacanth (pronounced “seel-uh-kanth”, selakanth in Afrikaans) is a large marine lobe-finned fish belonging to the Order Coelacanthiformes, a group of primitive bony fish. It became to be called the Coelacanthus after it was discovered that the spines were hollow (coel, Greek word for “space” and acanthus for spine). This was the first coelacanth to be described.
This fish is very important in that it is the sole living representative of a very ancient vertebrate group hence it provides scientists with a window to the past and also it comes from a very old lineage which dates back to 390 million years, preceding dinosaurs by more than 100 million years.
The coelacanth comes from a group of fish that was well known in the fossil record where they were once spread in seas and inland waters throughout the whole world. About 70 species of extinct coelacanths in four families and 28 genera are known. The coelacanth fossil record ended abruptly 70 million years. It is listed in Appendix 1 of the Convention on the International Trade in Endangered Species (CITES) which prohibits trade in this particular species.
The possibility that coelacanths had survived in deep seas was ignored. It was a great surprise on 22 December 1938 when Captain Hendriick Goosen, caught the first living coelacanth near the Eastern Cape Coat in South Africa. A search for the second coelacanth took 14 years and was caught off an island called Anjouan, Comoro Islands on 20 December 1952.
The Comoro Islands are located in between Mozambique and Madagascar. At least 177 coelacanths have been caught since 1938. The coelacanth at the Natural History Museum was caught by Comoran fishermen at Anj-ouan (Comoro Islands) in October 1978 and donated to the then
Rhodesian government. Mr. John Minshull ( The director of Queen Victoria Museum) was flown to collect the specimen. Coelacanths have survived the passing of time in more or less their original form, surviving terrific climatic changes and upheavals during the continental drift that wiped out many other animal species. Across these million years, countless other forms of fish evolved and flourished, but the coelacanth has outlived them all.
What does a Coelacanth look like?
An adult coelacanth can grow up to 1, 8m in length and weigh 95kg. It is dark blue in colour with pinkish white blotches that can be used by researchers when they are seen in their natural habitat underwater to designate individuals, but these change to grey/ brown after death.
The coelacanth has several very distinctive anatomical features. The skull is in two parts with an intracranial joint which is operated by a special muscle that allows up and down movement between them. The joint allows the coelacanth to open wide its large mouth which has bony plates and sharp cat-like teeth in order to swallow fish and other prey. The coelacanth is the only living animal with that structure today. The brain is tiny occupying about 1,5 percent of the brain case encased in a hardened skull. No known living vertebrae has so miniscule a brain in relation to its body size. The eyes are well developed with reflecting cells called tapetum “as in domestic cats” to enhance night vision by intensifying white light.
As a result, the coelacanth is virtually colour blind but can see extremely well in the dim light of the great depths where it lives.
Coelacanths belong to a group of bony lobe-finned fishes and have eight fins (two dorsal, two pectorals, two pelvises, one anal and one caudal). The lobed fins project from the body on stalks rather than attaching directly to the body as in other fish. The fins contain in their trunks bones mimicking those of Eusthenopteron (a lobe-finned fossil fish) which later developed into arms and legs in the ancestors of the amphibians.
The first dorsal fin of the coelacanth is much like that of other fishes. It can be folded down and move the fish from side to side. The other fins have a well developed muscular, arm-like basal lobe projecting the body wall, and a fringe of unbranched rays like a fan attached to the outer end of the stump. The fleshy scale-covered lobe can be bent or rotated so that the fish has the services of a mobile, strong, adaptable limb. The pectoral and pelvic fins are paired as can be seen as “pre-adaptations” to land locomotion. The right pectoral fin moves in conjunction with the left pelvic fin, the action that became four-legged land walking in their cousin Eusthenopteron’s descendants. The caudal fin (tail) is trilobated (divided into three sections) with a small tail fin in the middle. The tail is powerful, enabling the coelacanth to bolt forward in great thrusts to attack prey or escape predators.
The coelacanth is covered in scales that are thick, hard, woven tight and rough. They are lined with serrated rows of hardened tooth-like pointed denticles which give them their roughness and provide the coelacanth with protection against rocks.
Most of the skeleton is made of cartilage. There is no vertebral column but a notochord which is a hollow tube filled with an oil-like fluid. It extends from the skull to the tip of the caudal fin. It is tough and elastic and may act like a spring. It does the job of the backbone to the fish since no complete vertebrae are developed around it. In most other vertebrates the notochord disappears in the embryonic state of life.
The swim bladder lies beneath the notochord embedded in fat. In most fish, the swim bladder is filled with air but in the coelacanth it is packed with oil and fat. Its function is to increase buoyancy.
Coelacanths give birth to live young that are 32cm. The eggs are fertilised internally and are retained in the mother’s womb. Each egg is about 90mm in diameter and weighs 320g. Live bearing is a primitive feature and most fish do not give birth but lay eggs that are fertilized externally.
The coelacanth lives at a depth of 150- 300mm where water temperatures are between 13- 22ºC. It is respirationally stressed in warmer water and cannot survive for prolonged periods in shallow zones. The amount of oxygen which can be taken up from the water via the gills is susceptible to water temperature and distribution in natural habitat.
Being one of the most amazing pre-historic fish that is still alive, the Natural History Museum of Zimbabwe is privileged to house it. This helps us to look back in the past. Thus on the 14th of May 2012, the coelacanth display will be officially opened to the public so that everyone can have a look at this rare specimen that we have.
Ends.mavhu
Online Reporter