African Coelacanth (Biology)
The African coelacanth,Latimeria chalumnae,was thought to be extinct for 65 million years until an individualwas caught off the coast of South Africa in 1939. The African coelacanthis one of twomarine fishesin the family Latimeriidae, thesecondspeciesbeing the Indonesian coelacanth Latimeria manadoensis.An offshootlineageof the coelacanths played an importantrole in the evolution of vertebrates asthe Sarcoptergyiian fossil Tiktaalik roseaepresumablygave rise to the earliesttetrapods (terrestrial vertebrates).Latimeria's distantancestorsappeared 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 describedthroughout the fossil record. Throughout the 20th century, researchers have made progressuncovering the mysteries ofL. chalumnae since its discovery in 1939. However, there are still many unanswered questionsconcerning this relic ofancient waters. Are there other populations of L. chalumnaethrivingin the uppertwilight zonebesides 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 |
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Conservation Status  |
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Scientific Classification Kingdom: Animalia |
Physical Description
Thename 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,andsymmetrical, three-lobeddiphycercal 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 sensitiverostral organ, which functions for electroreception. The mouth is lined with small,sharp teeth.The gutcontains a spiral valve intestine, whichisdesigned to increasethesurface area of the intestineformore efficientdigestion. The gas bladder is filled with fat,which passively serves to regulatebuoyancy. 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.
Reproduction
Coelacanths are ovoviviparousfishes, likesome sharks, which exhibit internal fertilization and females retain theyoung in thebody while the embryos develop byfeedingon large yolk-sacs. It has also been shown that coelacanthpups feed oneggs produced by the mother's ovaries (oophagy). Coelacanth eggsare 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 sexuallymature at about 15 years of ageand produce relatively small litters of up to 29 pups. Gestationperiodis still a bit of a mystery, it may last as long as3 years, which would bethe longest gestationperiodof all thevertebrates.
Distribution & Movements
The onlyconfirmed population occurs in the Comoros Islands located between the northern most points ofMozambique andMadagascar. Estimated population size is 150-600 individuals.Individuals have been caughtalong the coasts of Kenya, Tanzania, Mozambique, and South Africa. The first specimen described to science by J.L. B. Smithwas caught in the estuary of theChalumna River, South Africa in1939.
Habitat
Coelancanthscan be foundin the mid epipelagicto the uppermesopelagic zones, 100 to 300 meters below the surface.Hardened lava slopesalong coastlinesare prime habitatfor L. chalumnae.Optimal temperature range isfrom 15-20ºC as coelacanths prefer colder, more oxygen rich waters.During the day, coelacanthsremain relatively inactive whilecongregated in small caves. As many as 17 individuals can be found concentrated in small cavesthroughout the day.By night,the nocturnal coelacanths migrate to deeper waters of200-500 meters below surfaceto feedindown and upwellings (currents). It is thought that the rostral organ used for electroreception could not onlyfunction for prey location, but also,in navigation as coelacanthsconsistentlyreturn to the same cavesthroughout their largehome ranges. Theretinasin the eyesof L. chalumnae have evolved toreceive a narrow range of colorsintheir light-depleted environment. Theretinas contain much more colorreceptivecone cells than light sensitive rod cells. Although, coelacanths do have a reflective layer (tapetum) in their eyes to make use ofwhat littlelight is present.
Food & Feeding Habits
Feeding observations have shown thatL. chalumnaeare piscivorous fish that hoover, by using their highly mobile paired fins, in currents waiting to ambush prey.An intracranialhinged jointallows the jaws toexpand and protrude,possibly allowingthe coelacanth to attack prey frombelow 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-developedlateral line system also contributes to prey location.Themassivecaudal fin and deep, muscular caudal peduncleproduceshort bursts of speed when ambushing prey. The first dorsal fin iscollapsed 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 waterin front of the fish. Preyis retained by bony, teethed gill rakers in the throat.
Predation
Adultscaught as commercialbycatch have been found missing fins. Thissuggests that deep-water sharks, possibly in the genusCentroscymnus or Hexanchus,attack andmay evenprey upon adult coelacanths. Juvenile L. chalumnae can presumablyfall 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 surfacewill soonperish 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, whichis also anuninviting traitfor a fish utilizedin consumption. Although, locals do use the oil from the skin asit is said toserve as anaphrodisiac.
Threats & Conservation Status
In 2000 the IUCN's redlist publishedL. 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 targetoilfish Ruvettus pretiosus, which has a high market demandin Japan. African coelacanths areespecially vulnerabledue to low reproductive output, small population size, and a limited geographic range. To further protect this charismatic species, the Coelacanth Conservation Council was formedand 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 giantpanda Ailuropoda melanoleuca represents terrestrial conservation for the World Wildlife Fund (WWF).
Further Reading
- 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.
- Helfman, Gene S., Bruce B. Collette, Douglas E. Facey, & Brian W. Bowen. 2009. The Diversity of Fishes: Biology, Evolution, and Ecology. 2nd edition. Wiley-Blackwell West Sussex, United Kingdom.
- Musick, J.A. 2000. Latimeria chalumnae in IUCN 2012. IUCN Red List of Threatened Species. Version 2012. <www.iucnredlist.org>.
- Torres, Armi G., & Rainer Froese. 2001. Reproduction of Latimeria chalumnae. <www.fishbase.org>.
- Thomson, Keith Stewart. 1991. Living Fossil: The Story of the Coelacanth. W. W. Norton & Company New York, New York.
- Yokoyama, Shozo, Huan Zhang, F. Bernhard Radlwimmer, & Nathan S. Blow. 1999.Adaptive evolution of color vision of the Comoran coelacanth (Latimeria chalumnae). Proceedings of the National Academy of Sciences Vol. 96: pg. 6283.
