Coelacanth: Rediscovery of the lost

Coelacanth for long have been considered as a “living fossil”, as scientists thought that they were the sole members remaining of a taxon which has only fossil records with no close relations alive. These species first appeared during Devonian period, roughly 400 million years ago and about 170 million years before the dinosaurs. On the basis of fossil records, they were thought to have been swiped during the mass extinction that wiped out about three quarters of Earth’s species following an asteroid strike at the end of the Cretaceous period. But to our surprise, these wondrous fishes have been found alive and well in 1938 near the east coast of South Africa.

What are Coelacanths?

A Latimeria chalumnae pup. This specimen is on loan to the National Museum of Natural History, from the South African Institute of Aquatic Biodiversity (SAIAB) and is currently on display at the NMNH Ocean Hall Exhibit. (Smithsonian Institution)
A Latimeria chalumnae pup. This specimen is on loan to the National Museum of Natural History, from the South African Institute of Aquatic Biodiversity (SAIAB) and is currently on display at the NMNH Ocean Hall Exhibit. (Smithsonian Institution)

Coelacanths are primitive osteichthyes or bony fishes which were once thought to have extinct until 1938 when it was rediscovered off the south african coast. They have four large, fleshy fins that act like limbs which some scientists believe could have been the predecessors of limbs. Based on the shape of its fins, which differ structurally from other fishes, they are often considered under class of lobed- fin fishes. Coelacanths are members of very rare order of fish (Coelacanthiformes) that includes two extant species in the genus LatimeriaThe West Indian Ocean coelacanth (Latimeria chalumnae) which is primarily found near the Comoro Islands of Africa and other being the Indonesian coelacanth (Latimeria menadoensis). They follow the oldest known living lineage of Sarcopterygii, which means they have close association with lung fishes and tetrapods, rather than to ray finned fishes.

The second Indonesian coelacanth known to science, later to become holotype (the reference specimen of a species) of the new species, Latimeria menadoensis. (Mark V. Erdmann)
The second Indonesian coelacanth known to science, later to become holotype (the reference specimen of a species) of the new species, Latimeria menadoensis(Mark V. Erdmann)

A Centenarian life span:

To determine the age of individual coelacanths, researchers used to read the annual growth rings deposited on the fish’s scales. It is very similar to the way how one reads the annular rings in tree. Previous research on African coelacanth using the same technique of age determination suggested that they have roughly a life span of 20 years and are among the fastest growing fishes. However, in recent studies, it has been proved to be a mis-reading of ring deposition on their scales. On the basis of new age estimation method, it appears that coelacanths are one of the slowest growing fishes among all other fishes. This new age estimation method employs the use of polarized light to study the scales. They are found to survive a life span of 100 years- “A centenarian life span which is quite something”.

Features which makes their life span peculiar:

  • As mentioned earlier that these ancient fish can live 100 years, meaning earlier estimates were off by a factor of five.
  • Females are somewhat larger than males, reaching about seven feet (two meters) long and weighing 240 pounds (110 kg).
  • Scientists have also studied two preserved Coelacanth embryos. They found that female coelacanths carry babies for at least five years before giving birth. A record gestation period, which exceeds the 3.5 years of frilled sharks and the two years of elephants and spiny dogfish sharks.
  • The female fish are not able to have babies until they are over 50 years old.
  • Coelacanths reside at ocean depths of as much as half a mile (800 meters). During daylight hours they stay in volcanic caves alone or in small groups.
  • The genome of the coelacanth (a deep-sea fish that closely resembles its ancestors, which lived at least 300 million years ago) revealed that some of the animal’s genes evolved very slowly as a result giving it its primitive appearance.

Slow to change:

The coelacanth can reach up to 2 metre long and is found lurking in caves deep beneath the waves. Researchers have sequenced the coelacanth’s genome, which contained nearly three billion DNA bases and what we can see is that while the genome as whole changes, the protein-coding genes – that make the living fish, are much more stable and much more unchanging. By this we can very well correlate to the fact that the coelacanth lives in a rather extreme and stable environment. They live several hundred metres down in the ocean where the environment doesn’t have a lot of competitors. So maybe it adapted to that environment a long time ago and it doesn’t have a huge need for change.

Future concerns:

Coelacanths are amongst the most primitive living fishes on this planet. Due to their late sexual maturity and a lengthy gestation period, combined with low fecundity and a small population size, these fishes are particularly sensitive to natural or human-caused environmental disturbances such as extreme climate events or too much accidental fishing.

We are already familiar to the threats imposed by us on majority of wildlife because of our self-centered and selfish activities. Thus, it is now our sole responsibility to contribute in their well being by not creating an imbalance in ecosystem, especially for those who are vulnerable to any kind of change in their surroundings.

References:

Websites: Smithsonian ; BBC News ; Current Biology Journal

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