|Porcupinefish (Diodon nicthemerus)
Photo by Mikkel Elbech
Porcupinefish are fish of the family Diodontidae, (order Tetraodontiformes), also commonly called blowfish (and, sometimes, balloonfish and globefish). They are sometimes collectively (but erroneously) called pufferfish, not to be confused with the morphologically similar and closely related Tetraodontidae, who are more commonly given this name.
Porcupinefish are medium to large sized fish, and are found in shallow temperate and tropical seas worldwide. A few species are found much further out from shore, wherein large schools of thousands of individuals can occur. They are generally slow.
Porcupinefish have the ability to inflate their body by swallowing water or air, thereby becoming rounder. This increase in size (almost double vertically) reduces the range of potential predators to those with much bigger mouths. A second defense mechanism is provided by the sharp spines, which radiate outwards when the fish is inflated.
Some species are poisonous, having a tetrodotoxin in their internal organs, such as the ovaries and liver. This neurotoxin is at least 1200 times more potent than cyanide. The poison is produced by several types of bacteria that are obtained via the fish's diet. As a result of these three defenses, porcupinefish have few predators, although adults are sometimes preyed upon by sharks and orcas. Juveniles are also preyed on by tuna and dolphins.
The Porcupine Fish (as Diodon Antennatus) is mentioned in Charles Darwin's famous account of his trip around the world The Voyage of the Beagle. He notes how the fish can swim quite fine when inflated even though the altered buoyancy requires it to do so upside down. Darwin also mentions hearing from fellow naturalist "Dr. Allen of Forres, that he has frequently found a Diodon, floating alive and distended, in the stomach of the shark; and that on several occasions he has known it eat its way, not only through the coats of the stomach, but through the sides of the monster" (Voyage 14).
Media related to Diodontidae at Wikimedia Commons
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