Episode 463: The Big Fish Episode

It's an episode just absolutely full of fish! Thanks to Arthur, Yuzu, Jayson, Kabir, Nora, Siya, Joel, Elizabeth, Mac, Ryder, Alyx, Dean, and Riley for their suggestions this week! Further reading: Study uncovers mechanics of machete-like 'tail-whipping' in thresher sharks Business end of a sawfish: Giant freshwater stingray! The frilled shark looks like an eel: The frilled shark's teeth: The thresher shark and its whip-like tail [photo by Thomas Alexander - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=50280277]: The Halmahera epaulette shark, looking a little bit like a long skinny koi fish [photo by Mark Erdmann, California Academy of Sciences, Attribution, https://commons.wikimedia.org/w/index.php?curid=30260864]: A mudskipper, which is a fish even though it kind of looks like a weird frog [photo by Heinonlein - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44502355]: The red-lipped batfish wants a big kiss: The male blue groper is very blue [photo by Andrew Harvey, some rights reserved (CC BY) - https://www.inaturalist.org/photos/62196538, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=157789928]: The giant oarfish is very long: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we have a big fish episode! I mean, it’s a big episode about a lot of different fish, not necessarily fish that are big—although some of them sure are! Thanks to Arthur, Yuzu, Jayson, Kabir, Nora, Siya, Joel, Elizabeth, Mac, Ryder, Alyx, Dean, and Riley. I told you this is a big fish episode. Let’s jump right in with a fish suggested by Jayson, the sawfish. There are five species of sawfish alive today. The smallest can still grow over 10 feet long, or 3 meters, while the biggest species can grow over 20 feet long, or 6 meters. The largest sawfish ever reliably measured was 24 feet long, or 7.3 meters. The sawfish lives mostly in warm, shallow ocean waters, usually where the bottom is muddy or sandy. It can also tolerate brackish and even freshwater, and will sometimes swim into rivers and live there just fine. The sawfish is a type of ray, and rays are most closely related to sharks. Like sharks, rays have an internal skeleton made of cartilage instead of bone, but they also have bony teeth. You can definitely see the similarity between sharks and sawfish in the body shape, although the sawfish is flattened underneath, which allows it to lie on the ocean floor. There’s also another detail that helps you tell a sawfish from most sharks: the rostrum, or snout. It’s surprisingly long and studded with teeth on both sides, which makes it look like a saw. The teeth on the sawfish’s saw are actual teeth. They’re called rostral teeth and the rostrum itself is part of the skull, not a beak or a mouth. It’s covered in skin just like the rest of the body. The sawfish’s mouth is located underneath the body quite a bit back from the rostrum’s base, and the mouth contains a lot of ordinary teeth that aren’t very sharp. Since the sawfish has plenty of teeth in its mouth, you may be wondering how and why it also has extra teeth on both sides of its saw. It’s because the rostral teeth evolved from dermal denticles. Dermal denticles look like scales but they’re literally teeth, they’re just not used for eating. Sharks have them too, along with some other fish. In the case of the sawfish, the rostral teeth grow much larger than an ordinary dermal denticle, and stick out sideways. Both the rostrum and the head are packed with electroreceptors that allow the sawfish to sense tiny electrical charges that animals emit as they move. This might mean a school of fish swimming through muddy water, or it might mean a crustacean hiding in the sand. The sawfish sometimes uses its rostrum to dig prey out of the sand, but it also uses it to slash at fish or other animals. Then the sawfish can either grab the injured or dead animal with its mouth or pin it to the sea floor with its rostrum to maneuver it into its mouth. Its mouth is relatively small and it prefers to swallow its food whole, head-first, so it can only eat fish that are smaller than its mouth. That’s also why it doesn’t want to eat people. Its mouth is too small. Yuzu wanted to learn about another shark relation, the giant freshwater stingray, which lives in rivers in southeast Asia. It’s dark gray-brown on its back and white underneath, and it has a little pointy nose at the front of its disc. It also has dermal denticles on its back. The giant freshwater stingray has a rounded, flattened body, and it’s really big. A big female can grow over 7 feet across, or 2.2 meters. Its tail is long and thin with the largest spine of any stingray known, up to 15 inches long, or 38 cm. Its tail is so long that if you measure the giant freshwater stingray by length including its tail, instead of by width of its disc, it can be as much as 16 feet long, or about 5 meters. Some researchers think there might be individuals out there much larger than any ever measured, possibly up to 16 feet wide. The length and thinness of the tail gives the ray its other common name, the giant freshwater whipray, because its tail looks like a whip. While we’re talking about shark relations, let’s go ahead and talk about a few actual sharks. Kabir wanted to learn about the frilled shark, which looks and acts more like an eel than a shark. A big female can grow up to 6 and a half feet long, or 2 meters. Males are a little shorter on average. The frilled shark has the same anatomy found in ancient sharks from the fossil record, dating back at least 95 million years. It’s found a body type that works for it. The frilled shark lives on the continental shelf in many parts of the world, and while it technically lives near the sea floor, at night it migrates closer to the ocean surface to find fish, squid and other cephalopods, and other food. There are two species known, with the southern African frilled shark only discovered in 2009. The frilled shark is dark brown or gray, and its jaws are long and contain clusters of teeth in little rows. Each tooth has three sharp points, and there are 300 teeth, so a frilled shark has 900 points in its mouth. The points are so sharp that scientists examining dead sharks have gotten cut on the teeth, which would be really embarrassing if you’re a shark expert that was bitten by a dead shark. The frilled shark can open its jaws extremely wide to swallow fish and other animals that are up to about half the size of the shark itself. It even eats other sharks. Next, Joel wanted to learn about the thresher shark. It’s a truly big fish that can grow up to 20 feet long, or over 6 meters. It’s a fast, slender shark with a tail fin that can be as long as its body. It eats a lot of other animals, including birds and crustaceans, but it specializes in hunting fish that travel in schools, like tuna, sardines, and mackerel. It uses its incredibly long tail as a whip, slapping a fish to stun it so the shark can eat it. When it whips its tail, its body flexes so that its head points downward in the water with the tail snapping forward over it. A 2024 study determined that the thresher shark’s vertebral column is fortified to allow it to work like a catapult. The thresher shark can also use its long tail to help it leap out of the water completely, although scientists don’t know why it wants to do that. There are three species of thresher shark known to science, but in 1995 a genetic analysis revealed the possible presence of a fourth species. Scientists think it lives in the eastern Pacific and may look similar to the bigeye thresher, enough that it gets misidentified as that species when it’s seen. The three known species of thresher shark are hard to tell apart at a distance as it is. And for our last shark, Siya asked about the Halmahera epaulette shark. It’s light brown with darker and lighter spots, and is a slender shark that can grow a little over 2 feet long, or 68 cm. It lives around Indonesia, and it might live in other places too. We don’t know yet, because it was only discovered in 2013 and only two specimens have ever been found. Epaulette sharks are also called walking sharks, because they use their fins to walk along the sea floor and explore crevices in rocks. Some species can even walk short distances on land to enter tidal pools and other places where they can find food. They live in warm, shallow water, usually near reefs or islands, and they eat whatever small animals they can find. There are nine species known, but there are undoubtedly more than haven’t yet been discovered by science. You might think this is strange for a shark that can walk on land, but walking sharks are nocturnal and not very big, so it’s easy to miss them when they’re out and about. That brings us to Arthur’s suggestion, the mudskipper. The mudskipper also uses its fins to walk. Its pectoral fins are muscular and allow it to climb out of the water and onto land, climb into low branches, and even jump. Its pectoral fins look like little arms, complete with an elbow. The elbow is actually a joint between the actual fins and the radial bones, which in most fish are hidden within the body but which stick out of the mudskipper’s sides a short distance. This helps it move around on land more easily. Its pelvic fins are also shaped in such a way that they act as little suction cups on land. The mudskipper is so good at living on land that it’s actually considered semi-aquatic. It lives in mudflats, mangrove swamps, the mouths of rivers where they empty into the ocean, and along the coast, although it prefers water that’s less salty than the ocean but more salty than ordinary freshwater. It only lives in tropical and subtropical areas because it needs high humidity to absorb oxygen through its skin and the lining of its mouth a