Paper: Mahé, K., Ernande, B., & Herbin, M. (2021). New scale analyses reveal centenarian African coelacanths. Current Biology.
We are still making sense of coelacanths. Thought to be extinct, these rare, critically endangered, 400 million-year-old ancient fishes are now thought to live for 100 years and might be in even more danger than previously thought.
Coelacanths: Our ancient and endangered cousins
Our fish ancestors looked less like Nemo, Dori, and 99% of modern-day fishes, and more like lobe-finned fishes – a rare group of fishes from which all tetrapods evolved (and yes, fishes is the correct term for more than one species of fish). The majority of them went extinct around 360 million years ago between the Devonian and Carboniferous periods. Coelacanths and lungfishes, however, while not our direct ancestors, are the only lobe-finned fishes alive today. Therefore, they provide a window to the past so that we can better understand our own lineage.
While the population of lungfishes is stable, coelacanths are rare and endangered. Thought to have gone extinct 70 million years ago, African Coelacanths (Latimeria chalumnae) were first discovered in 1938, while Sulawesi Coelacanths (Latimeria menadoensis) were discovered until in 1998. Both species inhabit remote benthic caves between 200 to 300 meters below sea level. According to the IUCN, African Coelacanths are critically endangered and Sulawesi Coelacanths are vulnerable. Their remote habitat and low numbers make them difficult to study and as a result, our knowledge about them is limited.
Making sense of their life-span
To make matters worse, we have conflicting information about coelacanths. The estimated life span of African Coelacanths is 20 years. With a body size that can reach 2 meters in length and weigh up to 105 kilograms, this evidence suggests that African Coelacanths are among the fastest-growing fish on the planet, on par with tuna, which are warm-blooded, fast-moving, deadly predators with a high metabolism. However, African Coelacanths could not be more different than tuna. They are ovoviviparous, produce a small number of offspring, move slowly, and have a slow metabolism. All characteristics of slow-growing fish.
New scale analysis reveals a long-lived coelacanth
To make sense of this discrepancy, scientists re-examined the methods used to study the age of coelacanths. Like trees, rings on a fish’s scales are used to determine the age of a fish. Previous studies counted readily visible rings called macro-circuli, to estimate the age of coelacanths. However, this time scientists used polarized light, which reveals more details of the scale’s topography. With this new method, scientists discovered tiny, previously unidentified rings called micro-circuli. Their results suggest that coelacanths are five times older than it was previously thought. Their lives span could reach 100 years old.
These results place coelacanths among the slowest growing fishes. The two embryos in this study were both five years old and growth models predict that male African Coelacanths reach reproductive age between 40 to 69 years old and females between 58 to 66 years. Their growth rates match the ones of other deep ocean fishes like deep-sea sharks and roughies.
Conservation
Coelacanths might be in even more danger than previously thought. Slow-growing animals have fewer offspring, but place a greater investment in their young so that they have a greater chance of survival. This survival strategy works under normal conditions but makes animals vulnerable to natural and man-made disasters. With fewer offspring, it takes longer for species to recover. With deep-sea trawling and shark nets often catching coelacanths, the recovery of the species might take a long time. The scientists in this study expect that their results will help to inform conservation and management efforts.
Hello! I am a science communicator who loves sharing stories about the ocean. In my free time, I enjoy running, spending time outdoors, doing puzzles and sipping on coffee while reading a good book. I am also an educator at the Museum of Science in Boston.
