Coelacanth Facts

The coelacanth (Latimeria chalumnae) belongs to a fish lineage with a fossil record extending back more than 400 million years. Because no confirmed coelacanth fossils younger than about 66 million years were then known, the living specimen hauled onto a South African fishing boat in 1938 surprised the scientific community. This deep-water fish grows up to about 6.5 feet in length and retains conspicuous traits such as fleshy lobed fins, a three-lobed tail, and an intracranial joint. Its lineage is ancient, but the living species has not remained frozen in time; our Journal article explains why the coelacanth is called a living fossil without being literally unchanged.

Scientifically designated as Latimeria chalumnae (the West Indian Ocean coelacanth), this fish is classified in the kingdom Animalia, phylum Chordata, and class Sarcopterygii, the lobe-finned fishes. Living coelacanths are the sole surviving lineage of the order Coelacanthiformes and belong to the family Latimeriidae.

Evolutionarily, Sarcopterygii is important because the group includes coelacanths, lungfish, and tetrapods—including amphibians, reptiles, birds, and mammals. The coelacanth's paired fins share deep homologous structures with tetrapod limbs, but living coelacanths form a side branch rather than a direct ancestral species. Their body plan retains several features also seen in fossil relatives, while both genetic and fossil evidence show that the lineage continued to change.

The coelacanth retains several anatomical traits that differ from those of modern teleost (bony) fishes. Rather than a solid, ossified vertebral column, the coelacanth's central axis is a large, thick-walled, fluid-filled tube known as a notochord.

Their locomotion differs from that of other living fishes. They possess fleshy, stalk-like pectoral and pelvic fins that articulate independently. When drifting, these paired lobed fins move in an alternating, diagonal pattern that resembles the trotting gait of a four-legged land animal.

Their skulls feature a true intracranial joint, a functional hinge that allows the upper jaw to swing upwards independently of the lower jaw when taking large prey items. The snout houses a specialized jelly-filled rostral organ that acts as an electroreceptor, detecting the faint electromagnetic fields generated by the muscle movements of hidden prey in the lightless depths. Their bodies are covered with thick, cosmoid scales that provide physical protection.

The West Indian Ocean coelacanth has a highly restricted and fragmented distribution. They are primarily found off the steep, volcanic coastlines of the Comoros Islands, with scattered populations recorded near South Africa, Tanzania, Mozambique, and Madagascar. A second species, the Indonesian coelacanth (Latimeria menadoensis), resides thousands of miles away in the waters of Indonesia.

They occupy rocky slopes and submarine caves in the deep marine benthic zone at depths ranging from 500 to over 2,300 feet. They occur below warm surface waters in the cold, pressurized environment of the deep ocean.

As apex deep-sea carnivores, coelacanths maintain a high-protein diet consisting of cuttlefish, squid, deep-water snappers, eels, and lanternfish. They are known to occasionally prey upon small, deep-water sharks.

Coelacanths hunt primarily at night. During the day, they aggregate in volcanic caves and remain relatively inactive in the low-oxygen environment. As night falls, they drift out of their caves, sometimes assuming a head-down vertical posture. They use their electrosensory rostral organ while moving near the seabed, detecting hidden benthic prey. Once a target is located, the coelacanth uses its lobed fins to pivot and its intracranial joint to open its jaws and take the prey.

Coelacanths gather during the day and are not strictly territorial. Aggregations sometimes numbering over a dozen individuals can rest side-by-side within a single submarine cave.

Despite this close physical proximity, observations have recorded little overt aggression, competition, or social interaction. No hierarchy, communication, or cooperative behavior has been documented. After sunset, individuals leave the cave to hunt alone and return to a communal cave near dawn.

Coelacanths reproduce slowly. They are ovoviviparous, meaning they produce eggs that are fertilized and develop entirely within the mother's body.

The gestation period of a coelacanth is estimated to last anywhere from 3 to 5 years, marking the longest known pregnancy of any vertebrate on Earth. Inside the mother, the developing pups nourish themselves on large yolk sacs. When the gestation period concludes, the female gives live birth to a litter of 5 to 25 fully formed, independent pups, each measuring about 14 inches long. The pups descend into deep reef crevices, where they have less exposure to larger deep-sea sharks. Coelacanths have a slow metabolism, and their wild lifespans are estimated to range between 60 and 100 years.

(Population and conservation trend data sourced from the IUCN Red List of Threatened Species)

The West Indian Ocean coelacanth is classified as "Critically Endangered" by the IUCN Red List. Wild population estimates range from a few hundred to a thousand individuals, and their slow reproductive rate increases their vulnerability to extinction.

Their primary threat is not targeted poaching—their oily flesh is foul-tasting and indigestible to humans. The main documented threat is deep-water fishing bycatch. As fishing operations extend trawls and deep-set longlines into deeper parts of the continental slopes after surface stocks decline, they can catch coelacanths and haul them to the surface, where pressure and temperature changes can kill them.

The coelacanth's body plan is best understood by comparison rather than by calling the animal unchanged. A leafy seadragon shows a highly derived shallow-water fish form, an ocean sunfish shows a distinctive open-water body plan, and a whale shark represents a cartilaginous lineage rather than a close relative. Their differences help place the coelacanth within living fish diversity.

• Smithsonian National Museum of Natural History: Coelacanth
• National Geographic: Coelacanth
• IUCN Red List of Threatened Species
• African Coelacanth Ecosystem Programme (ACEP)