Coelacanth: The ‘extinct’ fish found alive after 66 million years

Picture yourself dragging in your fishing net after a day at sea, only to catch a glimpse of a strange creature staring back at you, a creature that looks as if it just swam out of a fossil from the dinosaur age. This is what happened in 1938 to a fish that had been declared extinct for 66 million years. This "living fossil," named the coelacanth, challenged the assumptions of scientists and has become a reminder of the secrets that lie within nature. The coelacanth, a fish recognised for its fins and its prehistoric past, inhabits the ocean caves, a reminder that time and evolution do not apply to it. But now, with threats on the horizon, learning more about this prehistoric fish has never been more important. Its continued survival urges us to protect the fragile marine ecosystems it calls home, before this relic of Earth’s ancient past disappears for good.According to a paper published in Nature, the coelacanth's dramatic return began on 23 December 1938, when Captain Hendrik Goosen's trawler Nerine pulled up an odd fish near the Chalumna River (now Tyolomnqa). Museum curator Marjorie Courtenay-Latimer spotted it among the bycatch. Its blue-grey body, thick scales, and limb-like fins didn't match any known species. She sketched it and sent the drawing to ichthyologist J.L.B. Smith at Rhodes University. Smith recognised it instantly as a coelacanth, a fish known only from fossils dating back over 400 million years, with the last ones vanishing around 66 million years ago alongside the dinosaurs. "There was not a shadow of a doubt," Smith later wrote. "It could have been one of those creatures from 200 million years ago come alive again." He named it Latimeria chalumnae after Courtenay-Latimer and the river. By then, the specimen had been stuffed, ruining it for study, but the find sparked global excitement. Smith even offered a reward for another, leading to a second catch in 1952 off the Comoro Islands.Coelacanths earn their "living fossil" title through unchanged morphology since the Devonian period, over 410 million years ago. Adults grow to 2 metres long, weighing up to 90 kg, with a rounded body, broad head, and three-lobed tail. Their most striking trait? Lobed fins with bony stalks resembling early tetrapod limbs, hinting at fish-to-land evolution links. They dwell at 150-700 metres in rocky caves, emerging at night to hunt fish, squid, and eels. A low metabolism lets them survive on little food, possibly living 100 years. Females give live birth to pups after over a year of gestation, a rarity among fish. Genome studies reveal slow evolution. Researchers sequencing Latimeria chalumnae and L. menadoensis found tiny genetic divergence (0.18%), with heterozygosity rates as low as 0.0019% in Comoro individuals – far below humans' 0.069%. "The rates of heterozygosity of the coelacanth individuals from Tanzania, Comoros, and Indonesia were estimated to be 0.0023%–0.0024%, 0.0019%, and 0.0061%, respectively," the study noted on Britannica, pointing to small populations and sluggish mutation rates. Limb-related genes like bmp7 and gli3 enhancers are conserved between coelacanths and tetrapods, absent in ray-finned fish, suggesting ancient roots for land-walking traits. As per a study published in the National Library of Medicine, only two species remain: the African coelacanth (Latimeria chalumnae) in the Western Indian Ocean - Comoros, Tanzania, Madagascar, Mozambique, Kenya, and South Africa's Sodwana Bay - and the Indonesian coelacanth (L. menadoensis) around Sulawesi. The second species was discovered in 1998, extending the range. Genetic studies have identified populations, such as those in Tanzania, as different from those in Comoros. Recent eDNA studies have confirmed habitat. In 2022, researchers collected Jesser Canyon in Sodwana Bay's South African coast using ROVs and CTD bottles. Coelacanth eDNA was found in three of 15 samples, including one 5 km south, where none were expected. "Coelacanth eDNA was detected from three of 15 samples collected," the Biology Letters study concluded, confirming the test's specificity with primers Lati602F and Lati776R. Two of these were confirmed by ROV video of four individuals, demonstrating the effectiveness of eDNA for hard-to-detect species. This method could provide better distribution mapping, which is essential since both species are threatened with "critically endangered" status due to gillnet bycatch.Bycatch is a problem for coelacanths, particularly in Tanzania and Madagascar. Few individuals, possibly only hundreds and a low rate of reproduction make conservation difficult. Bottlenecks are evident in Comoro Island populations, reflected in low genetic diversity. eDNA provides hope. “Targeted eDNA sampling could potentially prove to be an effective and flexible approach to increase the rate and resolution at which coelacanth populations are surveyed and tracked,” according to the Royal Society study. Genomic knowledge calls for conservation. The rate of substitution is low, which explains the coelacanth’s lack of change but also its susceptibility. As Smith wrote in his book, a US scientist said after the discovery: “Now I can die happy for I have lived to see the great American public excited about fish.” Conserving caves and reducing nets is essential. This living fossil, back from 66 million years of extinction, demonstrates the power of resilience, but now requires our assistance to survive.