Saturday, 18 November, 2017

The Prehistoric Coelacanths

CF488CThe Coelacanth (pronounced seel-uh-kanth) is an enormous, bottom-dwelling fish that is unlike other living fish in a number of ways. They belong to an ancient lineage that has been around for thousands of years. Coelacanths can reach more than six feet long and weigh about 200 pounds, and they’re covered in thick, scaly armor. It’s estimated they can live up to 60 years or more. There are two living species of coelacanth, and both are rare. The West Indian Ocean coelacanth (Latimeria chalumnae) lives off the east coast of Africa, while the Indonesian coelacanth (Latimeria menadoensis) is found in the waters off Sulawesi, Indonesia. They are the sole remaining representatives of a once widespread family of lobe-finned fishes; more than 120 species are known from the fossil record.

scuba1Coelacanths were thought to be extinct until a live Latimeria chalumnae was discovered off the coast of South Africa in 1938. The second living species of coelacanth, Latimeria menadoensis, was discovered in an Indonesian market in 1997, and a live specimen was caught one year later.

coelacanth-living-fossil-fish-long-life-span_36320_600x450They have a unique form of locomotion. One striking feature of the coelacanth is its four fleshy fins, which extend away from its body like limbs and move in an alternating pattern. The movement of alternate paired fins resembles the movement of the forelegs and hindlegs of a tetrapod walking on land. Their jaws are hinged to open wide. Unique to any other living animal, the coelacanth has an intracranial joint, a hinge in its skull that allows it to open its mouth extremely wide to consume large prey. Coelacanths have a rostral organ in their snouts that is part of an electrosensory system. They likely use electroreception to avoid obstacles and detect prey. A coelacanth’s brain occupies only 1.5 percent of its cranial cavity. The rest of the braincase is filled with fat. After an extremely long gestation period, possibly up to three years, female coelacanths give birth to live offspring.

coelacanth-wallpaper-1During the day, coelacanths rest in caves and crevices. They leave these daytime resting places the same time late each afternoon to feed, mostly on fish and cephalopods. Coelacanths are passive drift feeders, moving lethargically near the ocean bottom and using the current and their flexible lobed fins to move about. During their nightly feeding ventures, they may travel as much as eight kilometers before retreating to a cave before dawn. More than a dozen coelacanths may seek shelter in the same cave; they don’t appear to show any aggression toward each other.

People, and most likely other fish-eating animals, don’t eat coelacanths because their flesh has high amounts of oil, urea, wax esters, and other compounds that give them a foul flavor and can cause sickness. They’re also slimy; not only do their scales ooze mucus, but their bodies exude large quantities of oil.

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