Coelacanth: Hunting and Diet

Summary: How does this deep sea fish find food? Just like everything else with the coelacanth, it’s fascinating! Join Kiersten as she explains how the coelacanth hunts and what it likes to eat. 

 

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

 

Show Notes:

“The coelacanth rostral organ is a unique low=resolution electro-detector that facilitates the feeding strike,” by Rachel M. Berquist, Vitaly L. Galinsky, Stephen M. Kajiura, and Lawrence R. Frank. Scientific Reports 5, #8962 (2015) https://doi.org/10.1038/srep08962

“The first direct evidence of a Late Devonian coelacanth fish feeding on conodont animals,” by Michel Zaton, Krzysztof Broda, Martin Qvarnstrom, Grzegorz Niedzweidzki and Per Erik Ahlberg. The Science of Nature 104, #26 (2017), https://doi.org/10.1007/s00114-017-1455-7

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

Music written and performed by Katherine Camp

 

Transcript

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

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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 and their diet and how they hunt is the sixth thing I like about them.

If you remember from episode two, Anatomy, coelacanths have what is called a rostral organ. This organ is believed to help them detect electric fields in their environment. Why do they need to detect electric fields? I love this question, listeners, and I’m proud of you for asking it! Some fish have the ability to detect weak, low frequency electric fields produced by living tissue that is in contact with water. These fish typically have some kind of electrosensitive organ that detects the electric fields and these fish tend to be meat eaters. See where I’m going with this?

The electric fields that living creatures give off is how the coelacanth finds its food. Let’s delve into the details of their rostral organ and see how this thing works.

Most fish with an electrosensitive organ that have been studied have complex labyrinths of hundreds to thousands of sensory canals. These canals are distributed throughout both the top and bottom of the head and are also often found around the mouth. These canals are typically arranged in clusters that are reminiscent of a directional antenna. All of the canals connect to an electrosensitive organ. The layout of the canals allows the fish to sense other animals near it from several different directions. This can help them find food, recognize conspecifics, or detect predators when they are at close range. Every animal’s electric field will be different and our fish can use those differences to discriminate between the animals near them. 

The coelacanth’s rostral organ is an electrosensitive organ but, just like everything else we’ve learned about so far, it’s not quite like other fish’s. To discover more about this organ, a team of scientists used an MRI machine on a preserved specimen of Latimeria chulumnae to get a good look at it. What they found was slightly unexpected but explained a few things that we’ll talk about in just a moment. 

The rostral organ of the coelacanth has only three sensory canals, as opposed to hundreds or thousands seen in other extant species of fish. These canals are called tubules and they are all restricted to a small area of the upper snout. They also have no electroreceptors connected to the lower surface of the snout or lower jaw. Seeing the smaller scope and size of the rostral organ, the researchers asked what good is it really doing the coelacanth. 

Using the 3D images they got with the MRI, they approximated the sensitivity of each tubule which allowed them to estimate the range of the rostral organ. What they found was that the coelacanth can only detect animals directly in front of their snout. Their rostral organ is only a low-resolution electro-detector so they do not get any complex information from the electric fields they detect and the field must be very close to them.

This makes them unique in living fishes that use electrosensory organs to detect prey because they cannot track the prey items movements. They have to wait until the prey is practically in their mouths before they sense them. Remember I said this studies’ findings explained something about the coelacanth, well the is it. It explains why they hunt the way they hunt.

When we first developed technology that allowed us to study live coelacanths in situ, we noticed a strange behavior. Sometimes coelacanths would drift along in a current with their heads down and their tails up, essentially in a headstand posture. We had no idea what was going on, until someone saw them snatch a fish. This is the way coelacanths hunt. 

It’s called drift hunting and it’s a passive way of hunting. The fish just floats along with the current of the water and waits for the right prey to come along. Then BAM!, dinner is served. This explains why their rostral organ is so focused on the snout region of their body. 

Once the coelacanth’s rostral organ indicates that an appropriate prey item has approached within 10 to 20 centimeters in front of its mouth, it snatches it out of the water. The specific feeding mechanism of the coelacanth is called suction-inhalation. I don’t think that really needs too much explanation. They suck their food into their mouth along with large amounts of water. This does explain why the coelacanth has such a large mouth. If you’re sucking your prey in whole, you want to have a big mouth. 

Coelacanths have well-developed protrusible jaws that are capable of great forward motion. Their extremely muscular lower jaw also contributes to their powerful suction-inhalation. They also have an expandable gular structure, under the chin, that helps increase the power and gape of the mouth. The intracranial joint that coelacanths have retained, while other species of fish have lost it through millennia of evolution, may also help with the flexibility of the head which in turn helps with mobility of the jaws.

This suction-inhalation does allow them to hunt animals that other fish of their size cannot reach. Researchers have seen coelacanth suck animals out of hidey holes in craggy canyon walls. And this method of cap ture is fast! It takes only a second for the coelacanth to inhale a prey item.

Inside the mouth, coelacanths do have three types of teeth. It does not appear that they use the teeth for grinding or shredding their food. It is more likely the teeth are there to prevent prey from escaping their giant maw.

Now that we know how coelacanth find their prey, what kind of prey are they looking for? This is a good episode for great questions, listeners. Y’all are on a roll today!

Coelacanths are classified as piscivores. Pisces is the Latin word for fish, but those of you born between February 19th and March 20th already knew that!  So a piscivore is an animal that eats fish. Coelacanth are not terribly picky about what they eat and their diet can include cuttlefish, squid, octopus, snipe eels, small sharks, and other benthic fishes. So, essentially whatever fits in their mouth. 

It appears they’ve been eating like this since the beginning of their time on earth. In a research paper published in 2017, the first direct evidence of a coelacanth eating eel like animals was discovered in the digestive tract of a fossilized specimen found in Poland. The coelacanth came from the Late Devonian period and a remnant of the eel was found preserved in the digestive tract. They also found coprolite, fossil poop, possibly from the coelacanth with the same remnants inside. We can’t know how these coelacanths hunted their food but we can now say that they’ve been eating the same kind of food for quite some time. 

In 2000, researchers looked at where coelacanths hunted, how abundant prey items were where they hunted, and how much food they might be eating.

They found that coelacanths hunted between 650 feet and 1300 feet below the surface of the water. They also measured prey density in relation to depth which increased as you descended deeper. I was a bit surprised by that actually. I thought there would be less prey as you moved further down. Maybe I need to do another series on some deep-sea wildlife.

They also estimated how much food the coelacanths were eating during each hunting session. Assuming the individuals studied were 100% successful on each hunt, medium-sized individuals were consuming about 122 grams of food and large females were consuming 299 grams of prey. Doesn’t seem like a lot considering an average sized Gala apple weighs between 150 to 250 grams. Although, an apple a day…right?

That’s all for this episode on the coelacanth. I hope you found their hunting behavior and their diet as fascinating as I did because it is my sixth favorite thing about them. 

 

 

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Join me next week for another episode about the coelacanth.  

 

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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.