Coelacanth: Reproduction

Summary: Coelacanth reproduction is the most mind-blowing episode yet! Join Kiersten as she digs deep into the life cycle of this ancient animal.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes: 

Anatomy: https://www.pbs.org/wgbh/nova/fish/anatomy.html

Vims Fish Collection: Coelacanth, https://www.vims.edu

Goliath Grouper - https://marinesanctuary.org

“New Scale Analysis reveal centenarian African coelacanths,” Kelig Made, Bruno Ernande and Marc Herbin, Current Biology 31, 3621-3628, August 2021. https://doi.org/10.1016/j.cub.2021.05.054

“Latimeria, the Living Coelacanth, Is Ovoviviparous,” by c. Lavett Smith, Charles S. Rand, Bobb Schaeffer, and James W. Ate. Science, 12 Dec 1975, Vol 190, Issue 4219, pp1105-1106; https://doi.org/10.1126/science.190.4219.1105

“‘Living fossil’ fish surprises scientists with 100-year lifespan,” by Thomson Reuters. Science, https://www.cbc.ca/news/science/coalacanth-fossil-1.6074328

Music written and performed by Katherine Camp

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

(Piano music stops)

Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

This episode continues the coelacanth series and the seventh thing I like about them is how they reproduce.

Strap in for this one listeners because this is the most mind-blowing episode of the coelacanth so far! 

There are so many unbelievable facts about coelacanth reproduction I almost don’t know where to start, but I have to start somewhere, so let’s start with their maturation age. 

Coelacanths are large fish averaging about five feet long with some individuals reaching six feet. With most large animals it takes some time to become mature enough to reproduce. For example, it takes elephants approximately ten years before they are ready to reproduce, blue whales, the largest animal alive today, mature around 15 years old, and Goliath groupers, a fish that can reach almost 8 feet in length, mature at about 20 years old. The coelacanth is no exception to this trend but they push it even farther than these three examples. A coelacanth becomes sexually mature at 55 years of age. That is an awful long time to survive before you can make more coelacanth. 

When coelacanths are ready to reproduce, a mate must be chosen. We don’t know what goes into this decision because we have not seen coelacanths copulating, yet. We don’t know what females look for in a mate, we don’t know if there is a mating ritual that males perform to attract females. We do know that most likely females choose the male and allow him to mate with her because fertilization is internal in coelacanths. I say this because other males of species that have internal reproduction or internal fertilization have various behaviors to attract females to them. The females pick the males that impress them most based on established criteria such as feather color, winning a fight with another suitor, or singing the best song. 

We’re already off to an unusual start because most scaled fish reproduce externally by laying eggs with males fertilizing the eggs after they are laid. Internal fertilization in fish such as sharks and rays is common but not so much in scaled fish.

We do know with some certainty that coelacanths are probably monogamous. In a scientific paper published in 2013, researchers genetically studied two clutches of coelacanth eggs and their mothers. Both coelacanth females were Latimeria chalumnae, the African Coelacanth. One female had 26 embryos and the other had 22 embryos. Both clutches appeared to be close to birth when the females were caught and perished. Let’s call the females with 26 embryos Clutch 1 and the female with 22 embryos Clutch 2. Results revealed that all the young of clutch 1 had four genotypes present. These were contributed by two individuals. The same results were reported for clutch 2. What exactly does this mean? It means only one male contributed his genetic material to the embryos. It was a different male for each female, but only one male contributed to the embryos. It’s an extremely small sample size, but this leads us to believe that coelacanths are monogamous. The females, at least, may only mate with one male at a time. 

Coelacanths are classified as ovoviviparous. For those of you who have listened to my caecilian series and remember the reproduction episode, you already know that ovoviviparous animals give live birth to animals that they incubate inside an egg that remains inside the female during development. This is what the coelacanth does. Now, you might be wondering how we know this since so much about their reproduction is still unknown. And that’s a great question, how do we know? 

In 1975, a gravid female was caught and upon dissection at the American Museum of Natural History, researchers found five young developing inside the oviduct of the coelacanth. These five young were attached to large yolk sacs. Since then other gravid females have been caught, as well, and dissection of these specimens has supported the findings of 1975. The female with 26 young in her oviduct appears to be the largest clutch discovered so far. 

Coelacanth eggs are pretty big. They are approximately 3 1/2 inches in diameter. Compare that to the average chicken egg at a diameter of 1 1/2 inches and you get a feel for how big their eggs get. When the young are born they are around 12 inches in length and they look like tiny versions of their parents. How long does it take a 3 1/2 inch egg to become a 12 inch fish? Probably longer than you think. 

Coelacanth females carry the young for up to five years. This is the longest gestation period of any animal that we are aware of at the recording of this podcast. Some species of sharks carry the young for three years. The coelacanth has them beat and it also explains why their eggs are so large. They need a good, long-lasting source of nutrition to develop properly. 

Once the young are born, we lose track of them. With the research we’ve been able to do with live coelacanths, we haven’t seen any young hanging around with adults so we assume that they must retreat to another habitat. There could be many reasons for this. They are much smaller than a full grown adult so they presumably eat different prey which means they could need a different environment in which to hunt. They might be escaping from their own parents territory because mom and dad might eat them. They may even move to higher depths or lower depths until they are much larger in size. Whatever the reason we have not seen any juvenile coelacanths, so for now their whereabouts remain a mystery.

The last thing we know about coelacanth reproduction is how long they live. For many years we thought they lived about 20 years and that they were extremely fast growing, but a study released in 2021 changed that. 

One way to determine a fish's age is to count the rings on their scales. Initial studies of coelacanth scales suggested a 20 year life span, but using a new technique involving polarized light researchers were able to see all the rings on the scales. The new data revealed that coelacanths can live up to 100 years. 100 years! This is also the study that determined they become sexually mature at 55 and they have a gestation period of five years. Who knew the rings on a fish’s scales could tell us so much?

That’s all for coelacanth reproduction. I still can’t get over all the amazing things I learned researching this episode and I know you are just as intrigued because it’s my seventh favorite thing about coelacanths. 

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another episode about the coelacanth.  

 

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.