Thanks to River for suggesting this week's topic, the pufferfish!

Further reading:

Grass puffer fish communicate with each other using a non-toxic version of their deadly toxin

Mystery pufferfish create elaborate circular nests at mesophotic depths in Australia

Pufferfish, puffed:





A starry puffer, un-puffed [picture by Diego Delso, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=116912671]:



A grass puffer, un-puffed:



The mystery structure that turns out to be made by pufferfish:



Show transcript:
Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.
This week we’re going to learn about a weird fish suggested by River, the pufferfish!
Lots of fish have the name pufferfish, and sometimes they’re also called balloonfish, swellfish, bubblefish, or globefish. You might be able to guess from the names what they can do, but just in case you don’t know, the pufferfish can puff up to make itself big and round. The question you might have at this point is why, and how do they do this?
There are lots of pufferfish in various genera, all of them in the family Tetradontidae. Tetradontidae means “four teeth,” because obviously when you find an incredibly poisonous fish that can blow itself up like a balloon, sometimes with spikes that emerge from the skin, of course you’re going to name it after its teeth.
Most pufferfish live in the ocean, although some live in places where freshwater mixes with ocean water, and some species even live in rivers. It prefers warm, shallow water and eats invertebrates and plant material. Larger pufferfish can use their four big front teeth to crush the shells of mollusks, like clams and mussels.
Most pufferfish are quite small and often brightly colored with spots, stripes, and other markings. You’d think the biggest pufferfish has to be the one called the giant freshwater pufferfish, but while it is big, it’s not the biggest. The giant freshwater pufferfish can grow up to 26 inches long, or 67 cm, which is over two feet long. But the starry puffer is almost twice that length, up to 47 inches long, or 120 cm. That’s almost four feet long!
The starry puffer lives in tropical and subtropical parts of the Pacific Ocean, especially in the Indian Ocean and the Red Sea. It has a big head, two pairs of nostrils, and is a mottled gray and white in color with little black spots all over. It mostly eats crustaceans and mollusks, but will also eat algae, sponges, coral, urchins, and other invertebrates.
The pufferfish is a slow swimmer, but it has two really good defenses. If it feels threatened—for instance if a big fish tries to catch it, or it’s caught in a fishing net and hauled to the surface, or if a diver tries to make friends, the pufferfish will swell up until it looks like a balloon with fins. It does so by gulping air or water into its elastic stomach until it’s completely full.
If you’re wondering how this can help the fish, not only does this make the pufferfish look much larger, it also makes it harder to swallow. Not only that, the pufferfish has spines that may be hidden in the skin most of the time, but when the skin tightens as the fish expands into balloon shape, the spines poke out. Suddenly a potential predator isn’t just trying to swallow a fish way bigger than its mouth is, it’s pointy.
The pufferfish’s second defense is that its body contains a deadly poison. You may have heard about fugu, which is considered a delicacy even though it’s so poisonous that in Japan and some other countries, chefs have to be specially trained and licensed to prepare the fish to eat. It contains tetrodotoxin, or TTX, a neurotoxin that stops your nerves from sending the tiny electrical signals that allow muscles to move. If you’re poisoned with TTX, you start to feel dizzy and sick, then you start having difficulty speaking and moving, then you have trouble breathing, and then, ultimately, you’re paralyzed and can’t breathe,