The African coelacanth, Latimeria chalumnae, was thought to be extinct for 65 million years until an individual was caught off the coast of South Africa in 1939. The African coelacanth is one of two marine fishes in the family Latimeriidae, the second species being the Indonesian coelacanth Latimeria manadoensis. An offshoot lineage of the coelacanths played an important role in the evolution of vertebrates as the Sarcoptergyiian fossil Tiktaalik roseae presumably gave rise to the earliest tetrapods (terrestrial vertebrates). Latimeria's distant ancestors appeared in the fossil record in the Middle Devonian (360 mya) and disappeared, with exception of the two extant species, alongside the dinosaurs in the late Cretaceous (80 mya). Coelacanths have a diverse past with 83 species described throughout the fossil record. Throughout the 20th century, researchers have made progress uncovering the mysteries of L. chalumnae since its discovery in 1939. However, there are still many unanswered questions concerning this relic of ancient waters. Are there other populations of L. chalumnae thriving in the upper twilight zone besides the Comoros Islands population? How long is the gestation period? Where do the coelacanths spawn?
Artist's rendition of the African coelacanth Latimeria chalumnae. Illustration credit: Charles Douglas, © Canadian Museum of Nature http://nature.ca/en/home
The name coelacanth is derived from Greek words coel (hollow) and acanth (spines) referring to the hollow nature of the spines in the first dorsal fin and caudal fin. Coelacanths are easily distinguishable by their lobed-fins, deep bodies, and symmetrical, three-lobed diphycercal caudal fin. The second dorsal, pelvic, anal, and caudal fins are lobed (Class Sarcopterygii = lobe-finned fishes). The coloration consists of an iridescent mauve blue background with white blotches distributed throughout the body. The scales are large, bony, and overlapping creating a sort of suit of armor. The snout encloses a highly sensitive rostral organ, which functions for electroreception. The mouth is lined with small, sharp teeth. The gut contains a spiral valve intestine, which is designed to increase the surface area of the intestine for more efficient digestion. The gas bladder is filled with fat, which passively serves to regulate buoyancy. L. chalumnae grows to 1.83 meters in length and 95 kilograms in weight. The lifespan of African coelacanth's average from 20-50 years in the wild.
Coelacanths are ovoviviparous fishes, like some sharks, which exhibit internal fertilization and females retain the young in the body while the embryos develop by feeding on large yolk-sacs. It has also been shown that coelacanth pups feed on eggs produced by the mother's ovaries (oophagy). Coelacanth eggs are the largest of any bony fish - 9 cm in diameter and 300 grams in weight. Females give birth to miniature versions of adult coelacanths. Females become sexually mature at about 15 years of age and produce relatively small litters of up to 29 pups. Gestation period is still a bit of a mystery, it may last as long as 3 years, which would be the longest gestation period of all the vertebrates.
Distribution & Movements
The only confirmed population occurs in the Comoros Islands located between the northern most points of Mozambique and Madagascar. Estimated population size is 150-600 individuals. Individuals have been caught along the coasts of Kenya, Tanzania, Mozambique, and South Africa. The first specimen described to science by J. L. B. Smith was caught in the estuary of the Chalumna River, South Africa in 1939.
Coelancanths can be found in the mid epipelagic to the upper mesopelagic zones, 100 to 300 meters below the surface. Hardened lava slopes along coastlines are prime habitat for L. chalumnae. Optimal temperature range is from 15-20ºC as coelacanths prefer colder, more oxygen rich waters. During the day, coelacanths remain relatively inactive while congregated in small caves. As many as 17 individuals can be found concentrated in small caves throughout the day. By night, the nocturnal coelacanths migrate to deeper waters of 200-500 meters below surface to feed in down and upwellings (currents). It is thought that the rostral organ used for electroreception could not only function for prey location, but also, in navigation as coelacanths consistently return to the same caves throughout their large home ranges. The retinas in the eyes of L. chalumnae have evolved to receive a narrow range of colors in their light-depleted environment. The retinas contain much more color receptive cone cells than light sensitive rod cells. Although, coelacanths do have a reflective layer (tapetum) in their eyes to make use of what little light is present.
Food & Feeding Habits
Feeding observations have shown that L. chalumnae are piscivorous fish that hoover, by using their highly mobile paired fins, in currents waiting to ambush prey. An intracranial hinged joint allows the jaws to expand and protrude, possibly allowing the coelacanth to attack prey from below or above. Two gular plates below the throat allow L. chalumnae to expand the throat when swallowing larger prey. The highly electrosensitive rostral organ in the snout allows the coelacanth to detect near-by prey. A well-developed lateral line system also contributes to prey location. The massive caudal fin and deep, muscular caudal peduncle produce short bursts of speed when ambushing prey. The first dorsal fin is collapsed when ambushing prey to reduce drag. Coelacanths use a suction mode of feeding, which is achieved by quickly expanding the buccal cavity (mouth) and creating a negative pressure relative to the water in front of the fish. Prey is retained by bony, teethed gill rakers in the throat.
Adults caught as commercial bycatch have been found missing fins. This suggests that deep-water sharks, possibly in the genus Centroscymnus or Hexanchus, attack and may even prey upon adult coelacanths. Juvenile L. chalumnae can presumably fall prey to a number of oceanic predators. Humans act as predators due to the fact that coelacanths are caught as bycatch. Coelacanths brought to the surface will soon perish due to a dramatic change in pressure and temperature at the water's surface.
Economic Importance for Humans
Coelacanths, due to their extensive media attention, have developed a sort of cult following. So much so that collectors have paid as much as $2,000 USD for individual coelacanth specimens. Coelacanths are not utilized for food possibly because coelacanths have heavy, bony scales making it difficult to fillet. The skin also produces copious amounts of slime, which is also an uninviting trait for a fish utilized in consumption. Although, locals do use the oil from the skin as it is said to serve as an aphrodisiac.
Threats & Conservation Status
In 2000 the IUCN's redlist published L. chalumnae as critically endangered. The Comoran government has also outlawed the capture of African coelacanths. Though, individuals are still caught as bycatch by commercial fishermen that target oilfish Ruvettus pretiosus, which has a high market demand in Japan. African coelacanths are especially vulnerable due to low reproductive output, small population size, and a limited geographic range. To further protect this charismatic species, the Coelacanth Conservation Council was formed and alternative fishing methods have been developed for Comoran fishermen. The coelacanth has been proposed to act as a symbol for aquatic conservation much like the giant panda Ailuropoda melanoleuca represents terrestrial conservation for the World Wildlife Fund (WWF).
- Fricke, Hans, Karen Hissmann, Jurgen Schauer, Olaf Reinicke, Lutz Kasang, & Raphael Plante. 1991. Habitat and population size of the coelacanth Latimeria chalumnae at Grand Comoro. Environmental Biology of Fishes Volume 32: pg. 287.
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