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From mudskippers to walking catfish to lungfish, air-breathing fish almost seem common! So to be a bizarre beast, you have to be extra weird, like gar are.

We want to thank Dr. Solomon David for pitching us these excellent fish and for all his help with the episode! Find out more about his work with gars on twitter:
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Host: Sarah Suta (she/her)
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Before this week, if I’d had to name one thing that separates the not-fish from the fish, it would’ve been breathing air. Yes, there are other obvious differences, too, like, feet but changing the whole system an animal uses to literally take in the molecules that keep it alive feels more important, somehow. Except, in working on this episode, I learned that sometimes some fish breathe air, too and, it turns out, there are a LOT more of them that do this than I had originally thought. For example, mudskippers. These little bug-eyed guys actually breathe through their skin when they’re on land. Yes, I said fish, on land. That is also very weird. And how about the walking catfish? Despite the name, they don’t actually have feet,  but they do have an accessory organ that lets them breathe air when they, like the mudskippers, decide to just leave the water. And then there’s the lungfish. Which, okay, fair enough, they have lungs, it’s in the name, I can’t really be that surprised about that one. What I’m trying to say is, if you’re an air-breathing fish, there has to be something else weird about you to make you a Bizarre Beast. Good thing gars have that.

 [ ♪ Intro ]

 Today, there are seven living species in the gar family, and they’re only found in the Americas from as far north as southern Canada to as far south as Costa Rica. They mostly live in warm, shallow freshwater habitats, like lakes and rivers, but some species, like the alligator gar, which can grow to more than 3 meters in length,  also venture into brackish and saltwater. And where they live is really important. It’s what makes their ability to breathe air a useful adaptation, instead of just a neat party trick, and it might be partially responsible for one of their other strange traits. See, you and I, we’re “obligate air-breathers.” We don’t have any other way to take in oxygen. But gars are considered “facultative air-breathers.” They have gills that take in oxygen from the water they’re in, like a normal fish, but when that water is low in oxygen, they can surface to gulp air into a specialized swim bladder. They have oxygen options. And warm, shallow, slower-moving water tends to have less dissolved oxygen in it than cold, fast-moving water. In fact, one study found that gars breathe air more often when the water they’re in is warmer. So gars can survive in places that other fish, ones that only have gills, can’t.

And one of the things they do in those lower-oxygen places is reproduce. Female gars lay thousands of eggs at a time. And the different species have slightly different preferences about where they lay their eggs. For example, alligator gar spawn in the shallow, grassy floodplains formed when rivers flood their banks. Longnose gar prefer to lay their eggs in gravelly or weedy places in small, fast-moving streams. And Florida gar like a weedy backwater or a shallow pool. But one thing all gar eggs, or roe, have in common is that they’re poisonous, but only to some animals. Experiments where mice and crayfish were fed gar roe went...badly for those critters. And the eggs are also toxic to birds. And for humans? No gar caviar for us, either, thanks.Case reports from the emergency room on people who’ve made the mistake of trying it promise nausea, sweating, vomiting, and diarrhea. Not fatal, but definitely not a good time. To quote my co-host, Hank Green, here: “don’t eat that!”

Fish and red eared turtles, though, don’t seem to react to the toxin if they’re fed the eggs. And the fact that fish aren’t affected might have to do with the whole gar air-breathing thing. Mammals, birds, and arthropods like crayfish can potentially hang out in the kinds of lower-oxygen environments that gar frequent,  but other fish can’t. So maybe gar eggs are only poisonous to the kinds of animals that’ve been around to potentially prey on them. Or it might just be chance. Regardless, it’s pretty rare. Only something like 10 genera of fish out of over 5200 are known to have poisonous roe. As for what makes the eggs toxic, well, researchers seem to only kinda know. It’s usually just called ichthyotoxin, which means a toxin that’s made by a fish. So, not very specific. It seems to be slow-acting and the amountthat’s consumed does seem to matter.

One very weird experiment that applied alligator gar roe extract to isolated turtle hearts suggested that, whatever the toxin is, it somehow messes up the ability of cells to maintain the balance of calcium ions they need to function correctly. So, it looks like, while some turtles can eat the eggs,  applying the toxin directly to their hearts still goes badly for them. And no, I have no idea why they tried that. The study actually doesn’t say. Just don’t eat gar eggs. Seriously. You can eat their meat though, if that’s something you’re into, if you can get to it. You’re going to need something more heavy-dutythan a fillet knife, because gar scales are basically fishy armor. Along with regular bone, those scales are also made up of a material called guanine, which seems to be closely evolutionarily related to tooth enamel! You know, the hardest substance in your entire body.

 Gars aren’t the only fish with this kind of scale, either. Bichirs also have ganoid scales, and, like gars, are the living representatives of a really ancient lineage of fish, both groups separately split off from the rest of the family tree of fish more than 200 million years ago. Gars are survivors. Between the poisonous eggs and armored scales,it’s kinda no wonder they’ve stuck around for as long as they have. And what I think is really funny about this whole story of a weird family of fish is that it started off with the one thing they share in common with us: the ability to breathe air.

 First off, we want to thank Dr. Solomon David for pitching us on these excellent fish and for all of his help with the episode! If we’ve made you a fan of gars, subscribe to the Bizarre Beasts pin club and get one for yourself! The subscription window is open from now through April 4th. If you sign up now, you’ll get your fantastic gar pin in the middle of the month and the pins after that around the time each new video goes live. And if you missed the pin sign up, but love weird animals, we have other merch! You can still get a Bizarre Beasts tote bag and stickers at As always, profits from the pin club go to support our community’s efforts to decrease maternal mortality in Sierra Leone.

 [ ♪ Outro ]