Fish once labeled a 'living fossil' surprises scientists again
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[June 19, 2021]
By Will Dunham
(Reuters) - The coelacanth - a wondrous
fish that was thought to have gone extinct along with the dinosaurs 66
million years ago before unexpectedly being found alive and well in 1938
off South Africa's east coast - is offering up even more surprises.
Scientists said a new study of these large and nocturnal deep-sea
denizens shows that they boast a lifespan about five times longer than
previously believed - roughly a century - and that females carry their
young for five years, the longest-known gestation period of any animal.
Focusing on one of the two living species of coelacanth (pronounced SEE-lah-canth),
the scientists also determined that it develops and grows at among the
slowest pace of any fish and does not reach sexual maturity until about
age 55.
The researchers used annual growth rings deposited on the fish's scales
to determine the age of individual coelacanths - "just as one reads tree
rings," said marine biologist Kélig Mahé of the French oceanographic
institution IFREMER, lead author of the study published this week in the
journal Current Biology.
Coelacanths first appeared during the Devonian Period roughly 400
million years ago, about 170 million years before the dinosaurs. Based
on the fossil record, they were thought to have vanished 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.
After being found alive, the coelacanth was dubbed a "living fossil," a
description now shunned by scientists.
"By definition, a fossil is dead, and the coelacanths have evolved a lot
since the Devonian," said biologist and study co-author Marc Herbin of
the National Museum of Natural History in Paris.
It is called a lobe-finned fish based on the shape of its fins, which
differ structurally from other fish. Such fins are thought to have paved
the way for the limbs of the first land vertebrates to evolve.
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. Females are somewhat larger than males, reaching about
seven feet (two meters) long and weighing 240 pounds (110 kg).
The two extant species, both endangered, are the African coelacanth,
found mainly near the Comoro Islands off the continent's east coast, and
the Indonesian coelacanth. The study focused on the African coelacanth,
using scales from 27 individuals in two museum collections.
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Staff of department of fish studies at the National Museum of Kenya
on Nov. 19, 2001, display a coelacanth fish caught by Kenyan
fishermen at the coastal town of Malindi in April 2001.
REUTERS/George Mulala/File Photo
Previous research had suggested roughly a 20-year
lifespan and among the fastest body growth of any fish. It turns out
that this was based on a misreading decades ago of another type of
ring deposited in the scales.
"After reappraisal of the coelacanth's life history based on our new
age estimation, it appears to be one of the slowest - if not the
slowest - among all fish, close to deep-sea sharks and roughies,"
said IFREMER marine evolutionary ecologist and study co-author Bruno
Ernande.
"A centenarian lifespan is quite something," Ernande added.
The Greenland shark, a big deep-ocean predator, can claim the
distinction of being Earth's longest-living vertebrate, with a
lifespan reaching roughly 400 years.
Ernande said the researchers were astounded when they figured out
the coelacanth's record gestation period, which exceeds the 3.5
years of frilled sharks and the two years of elephants and spiny
dogfish sharks.
The researchers said late sexual maturity and a lengthy gestation
period, combined with low fecundity and a small population size,
makes coelacanths particularly sensitive to natural or human-caused
environmental disturbances such as extreme climate events or too
much accidental fishing.
(Reporting by Will Dunham in Washington, Editing by Rosalba O'Brien)
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