| Name | Coelacanths | Diet | Carnivorous |
| Scientific name | Latimeria | Weight | 90 kilograms (200 pounds) |
| Pronunciation | SEE-luh-kanth. | Length | 2 meters (6.6 feet) |
| Classification | Actinistia, Coelacanthiformes, Latimeriidae | Location | East coast of Africa & Indonesia |
The Coelacanth
The coelacanth is a large bottom-dwelling fish, unlike any other living fish species you have ever seen.
That’s because this fish belongs to the prehistoric past, and the fact that it’s still living today is in itself a miracle.
Until 1938, the coelacanth was only known from fossils.
It was assumed to have gone extinct during the end-Cretaceous extinction event about 65 million years ago.
The coelacanths were once a large group of lobe-finned fish with up to 90 species living in freshwater and marine environments worldwide.
Today, only two living species are left, but they have remained relatively unchanged despite being alive for more than 360 million years.
Modern coelacanths are bigger than their extinct ancestors known from the fossil record.
They’re powerful predators known to feed on smaller fishes and other marine prey.
In this article, we’ll explore all the fascinating facts about this group of fish that’s often described as a living fossil because of how long ago it evolved.
Taxonomy and Classification
The name coelacanth refers to any of the two living species of lobe-finned fishes in the Latimeria genus.
The two species in the genus are Latimeria chalumnae (also known as the West Indian Ocean coelacanth) and Latimeria menadoensis (Indonesian coelacanth).
Sometimes, the name is also used to refer to their other relatives within the Coelacanthiformes Order.
This is a broad group of lobe-finned fish, meaning they belong to the Sarcopterygii subclass of bony fish.
Members of this group are characterized by their possession of muscular buds in their fins instead of bony spines like the ray-finned fishes (Actinopterygii).
Coelacanths are more closely related to the lungfish and tetrapods (amphibians, reptiles, birds, and mammals) than they are to the ray-finned fish species.
Living coelacanth species are often described as “living fossils” because of how long ago they lived and their primitive appearance.
Early coelacanths likely evolved about 410 million years ago and were quite widespread during the Devonian Period, about 360 million years ago.
Experts initially assumed that they went extinct during the Late Cretaceous Period, about 66 million years ago.
However, a live coelacanth was caught in 1938, showing that this family of lobe-finned fish survived long beyond this period.
Physical Characteristics
Modern coelacanths are relatively large fishes with an elongated cylindrical body and a rounded snout.
They can grow to an average length of about two meters (6.6 feet) and weigh up to 90 kilograms (200 pounds).
Coelacanths have eight fins.
They have two dorsal, pectoral, and pelvic fins, while they have one anal fin and one caudal fin.
The pectoral and pelvic fins of this fish are robust and fleshy.
That’s because they’re supported by limb-like bones.
This type of fin is referred to as “lobed fins” and is considered a precursor to the limbs of terrestrial vertebrates (tetrapods).
The caudal fin (tail fin) is symmetrical and consists of three lobes.
The upper and lower lobes are of equal size.
Coelacanths have several primitive features not seen in other living fish species.
For instance, they’re the only fish species with an intracranial joint.
This is a type of hinge on the skull that allows them to swing the anterior portion of their skull upward, enlarging their gape significantly.
They also have a “rostral organ” on their snout, which serves an electrosensory purpose.
The backbone of this fish consists of a hollow, fluid-filled “notochord,” which extends through the entire length of their body underneath their spinal cord.
This notochord has been replaced by a bony vertebral column in most adult vertebrates.
Coelacanths are typically blue to brownish-black in color.
The specific color depends on the species.
The Indonesian coelacanth is brownish-gray, while the West Indian Ocean variety has a bluish hue.
Both species have mottled spots on their body, a form of disruptive coloration that helps them blend into their deep-sea environment.
Habitat and Distribution
Coelacanths are marine fish species known for their preference for deep-sea environments, typically near the continental slope.
They inhabit depths of about 180 to 200 meters (600 to 650 feet).
Although some individuals have been observed at greater depths, this range is more common.
This deep-sea environment occupied by this fish is characterized by low light conditions since sunlight does not penetrate to such depths.
Coelacanths have large eyes and sensitive electroreceptive organs to help them navigate and locate prey in the darkness of their habitat.
This fish is typically associated with steep, rocky, and rugged areas on the continental slopes.
These underwater formations provide crevices and caves where coelacanths can seek shelter to hide or rest.
As the name suggests, the West Indian Ocean coelacanth (Latimeria chalumnae) lives in parts of the Indian Ocean off the eastern coast of Africa.
It has been found in the waters of various east and southern African countries, including Kenya, Mozambique, Tanzania, and South Africa.
A few individuals have also been caught around the Islands of Comoros Archipelago all the way past the western coast of Madagascar.
The Indonesia coelacanth (Latimeria menadoensis) has a geographical range along the coast of Manado Tua Island and Indonesia.
It’s important to note that coelacanths are rare and elusive.
Their distribution is limited to specific deep-sea environments, and this has made it challenging to determine their exact range and distribution.
Behavior and Social Structure
Coelacanths are slow-moving fish that inhabit deep-sea habitats.
They have a unique form of locomotion, which involves using their paired fleshy fins to stabilize their body as they drift through the water along with the ocean currents.
The fleshy fins extend away from their body and move in alternative patterns similar to tetrapod limbs.
But coelacanths don’t use their fins for locomotion on the seafloor.
Instead, they use their caudal fins to generate quick thrusts.
Coelacanths are highly maneuverable and can orient their body in almost every direction while swimming.
Although they live in deep-sea environments with very limited light penetration, coelacanths have large eyes adapted for seeing effectively in poor light conditions.
They also have a well-developed electroreceptive system that can detect electrical signals generated by their prey.
Coelacanths are primarily nocturnal, meaning they are more active during the night.
They spend the day in underwater caves or crevices that provide shelter from potential predators.
They forage at night when fish and other marine prey are more abundant.
Coelacanths are not territorial, and they remain fairly peaceful even when they encounter others of their kind.
They have been known to remain calm even in crowded caves.
They’re non-migratory, although they tend to cover vast areas of their deep-sea home while foraging for food.
Coelacanths are generally solitary and non-social creatures.
While multiple individuals may be found in the same area, they do not form long-term pairs, groups, or herds.
This is beneficial for them since resources tend to be scarce in the deep-sea environment where they live, favoring a more solitary lifestyle.
Diet and Feeding
Coelacanths are piscivores, which means they feed mainly on fish.
Their diet consists of small fish species that are abundant in the benthic environment where they live.
However, they may also prey on squids, octopuses, and other cephalopods.
They are opportunists, meaning they feed on various prey animals depending on what’s available within their habitat.
Some known prey species of the West Indian Ocean coelacanth include the goatsbeard brotula, rattails, and beryx fish.
Coelacanths are not agile predators.
They are “passive drift feeders” that drift slowly in the water, propelling their bodies minimally.
They have to wait for prey to drift close before lunging at it with their large mouth.
Coelacanths also have an advanced electroreceptive system to detect weak electrical signals produced by the muscles and nerves of prey.
This sensory adaptation is crucial in the dark, deep-sea environment where visibility is limited.
Thanks to their intracranial joints, coelacanths can open their mouths really wide.
This wide gape allows them to swallow relatively large prey whole.
Reproduction and Life Cycle
Coelacanths live in deep-sea environments, and this makes it challenging to observe many of their habits, including how they reproduce in the wild.
Consequently, we know very little about the specifics of their mating rituals, copulation, and birth.
We do know that they exhibit internal fertilization, which involves the transfer of sperm into the body of the females by a specialized organ or structure.
Female coelacanths may carry between 20 and 65 eggs that are fertilized internally.
They are ovoviviparous, which means the eggs will develop within the female’s body, and the young are born alive.
Coelacanths have a relatively long gestation period.
While the exact duration has not been adequately documented, some estimates suggest it lasts up to five years.
Coelacanths give birth to five to 26 pups after their long gestation period.
The pups are born alive and are fully developed by the time they’re found.
They receive no parental care since they’re born relatively mature and equipped to survive in their deep-sea environment.
Juveniles are equipped with functional lobed fins and other characteristic features of an adult coelacanth.
They’re also capable of hunting small prey on their own shortly after birth.
Coelacanths exhibit indeterminate growth.
This means they continue to grow throughout their life.
Their growth rate is slow, and they have a very long lifespan.
Older individuals tend to have more iridescent spots on their bodies compared to juveniles.
The estimated lifespan for a coelacanth is about 100 years.
This is based on an analysis of growth marks on their scales.
It takes several years for this fish to reach maturity, typically around age 55.
Ecological Role and Interactions
Coelacanths are top predators in the deep-sea marine environment where they live.
They prey mainly on fish and cephalopods, and their feeding activities help regulate the population of their prey species.
This prevents overpopulation and overexploitation of marine resources by these prey species, which could disrupt the balance of the local ecosystem.
Regulating prey populations this way also has a cascading effect on the entire food web.
Coelacanths themselves are prey to bigger fishes within their ecosystem.
Sharks are the major predator of this primitive fish, and they’re quite common in the areas inhabited by the coelacanths.
A few coelacanth individuals have also been found with shark bite marks on them, further supporting the idea that they’re preyed on by sharks.
Conservation Status and Threats
Coelacanths are rare and elusive creatures, so much so that they were once considered extinct.
Today, there are still two species of this fish living in the waters of the Indian Ocean.
But they’re not quite abundant yet.
Latimeria chalumnae (West Indian Ocean coelacanth) is critically endangered.
The Indonesian or Sulawesi coelacanth (Latimeria menadoensis) is also categorized as a vulnerable species by the IUCN.
Coelacanth populations are at risk because of their slow rate of reproduction.
Giving birth to a few offspring after a five-year-long gestation period makes the species vulnerable to simple environmental factors such as predation and habitat loss.
Coelacanths are deep-sea inhabitants.
Human activities that threaten or destroy their typical habitat, such as deep-sea mining, can adversely affect their populations.
Commercial fisheries do not typically target coelacanths.
However, they’re sometimes accidentally caught in deep-sea trawl nets, which can also threaten their populations.
Efforts to conserve the coelacanths are currently focused on researching their population, understanding them, and tracking their distribution across their current known range.
This will make it easier to devise strategies that will help protect the unique habitats of these fish species.
Conservation measures may also include implementing regulations to reduce bycatch and introducing selective fishing methods that will help protect coelacanths from commercial fishing activities.
Unique Adaptations and Survival Strategies
One of the most distinctive features of coelacanths is their lobed pectoral and pelvic fins.
Thick, limb-like bones support these fins, and their robust nature allows for precise control of the fish’s movement in the water.
This crucial adaptation helped animals evolve from fish to terrestrial tetrapods (four-limbed vertebrates).
Another unique adaptation of the living coelacanth species is their fatty lungs.
This is a fat-filled organ that performs a similar function as the swim bladder of modern fish species.
The organ helps the coelacanths control their buoyancy, which is an essential adaptation for their deep-sea habitat.
The parallel development of a fatty organ for buoyancy control suggests a unique specialization for deep-water habitats.
Cultural Significance and Human Interactions
Although only a handful of living coelacanth individuals have been found so far, this fish holds immense significance, especially in the scientific world.
It is commonly referred to as a living fossil because of how long ago the fish evolved.
The rediscovery of the coelacanth in 1938 was a monumental event in paleontology and evolutionary biology.
Finding a species that was assumed to be extinct all this while is similar to finding a dinosaur alive today and generated significant buzz when it occurred.
Consequently, the coelacanths are still regarded as symbols of prehistoric life and evidence of how long life has persisted on the planet.
Even more significant is the evolutionary status of the coelacanth as a possible bridge between aquatic and terrestrial life.
The limb-like fins of this fish are one of the most remarkable adaptations that made the transition of life from fully aquatic to terrestrial possible.
People generally don’t eat coelacanths because they don’t taste good.
Their flesh contains high amounts of urea, oil, wax esters, and other compounds, which give them a foul flavor.
Future Prospects and Research
Since their rediscovery, scientists have been interested in studying coelacanths and better understand their genetic composition.
As one of the oldest species of lobe-finned fish that is still alive today, coelacanth’s genome might hold the key to understanding the evolution of vertebrates, including humans.
Scientists are also trying to understand the genetic adaptations that allowed coelacanths to survive for so long.
These studies will have a wide range of implications in the fields of paleontology and evolutionary biology.
Researchers are also using genetic analysis to better understand the populations and genetic diversity of coelacanths.
The genetic relationship between the two living species of this fish may provide vital information needed for their conservation and that of other vulnerable species in Earth’s oceans worldwide.
Conclusion
Coelacanths are among the most bizarre living species today.
Once thought to be extinct, the discovery of two living species of this prehistoric fish is one of the most significant scientific miracles of the past century.
Coelacanths live off the east coast of Africa and in the waters of the Sulawesi Sea in Indonesia.
They’re deep sea dwellers known to prey on small fish and crustaceans.
Coelacanth populations are yet to rebound fully and may never do so because of their low reproduction rate.
This is why we have to speed up efforts to learn more about them and protect the few individuals that are still living today.
Sources:
- https://en.wikipedia.org/wiki/Coelacanth
- https://en.wikipedia.org/wiki/Indonesian_coelacanth
- https://en.wikipedia.org/wiki/West_Indian_Ocean_coelacanth
- https://www.britannica.com/animal/coelacanth
- https://ocean.si.edu/ocean-life/fish/coelacanth
- https://australian.museum/learn/animals/fishes/coelacanth-latimeria-chalumnae-smith-1939/
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