Diodon Explained

Porcupinefishes or balloonfishes, are any of the various species of the genus Diodon, the type genus of Diodontidae.

Distinguishing features

Fish of the genus Diodon have:

• two-rooted, movable spines (which are derived from modified scales) distributed over their bodies.
• beak-like jaws, used to crush their hard-shelled prey (crustaceans and molluscs).

They differ from the swelltoads and burrfishes (genera Cyclichthys and Chilomycterus, respectively), which, in contrast, have fixed, rigid spines.

Defense mechanisms

• Like true pufferfishes of the related family Tetraodontidae, porcupinefishes can inflate themselves. Once inflated, a porcupinefish's erected spines stand perpendicular to the skin, whereupon they then pose a major difficulty to their predators: a large porcupinefish that is fully inflated can choke a shark to death. According to Charles Darwin in The Voyage Of the Beagle (1845), Darwin was told by a Doctor Allen of Forres, UK that the Diodon actually had been found "floating alive and distended, in the stomach of the shark" and had been known to chew its way out of shark bodies after being swallowed, causing the death of its attacker.^[1]
• They may be poisonous, through the accumulation of tetrodotoxin or ciguatera.^[2]

Species

Extant

There are currently five recognized extant species in this genus:^[3]

Image	Scientific name	Common Name	Distribution
	Diodon eydouxii Brisout de Barneville, 1846	Pelagic porcupinefish	circumtropical distribution
	Diodon holocanthus Linnaeus, 1758	Long-spined porcupinefish	tropical zones of major seas and oceans
	Diodon hystrix Linnaeus, 1758	Spot-fin porcupinefish	tropical and subtropical waters of the world, including the Mediterranean Sea
	Diodon liturosus G. Shaw, 1804	Black-blotched porcupinefish	tropical and subtropical waters of the Indo-Pacific area from eastern coasts of Africa to Japan
	Diodon nicthemerus G. Cuvier, 1818	Slender-spined porcupinefish	southern Australia, as far north as Port Jackson to Geraldton, Western Australia

Fossil

Fossils of porcupinefishes are known from Tertiary-aged marine strata. These species are similar to modern species. Fossil species include:

• Diodon tenuispinus, from the Ypresian-aged Monte Bolca lagerstatte.
• Diodon scyllai, from middle Miocene-aged Piemonte, Italy.

Notes and References

1. Book: Darwin, C.. Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy, R.N. 2d edition. 1845. John Murray. London. 14.
2. Lieske, E. & Myers, R.F. (2004): Coral reef guide; Red Sea London, HarperCollins
3. Matsuura . K . 2014 . Taxonomy and systematics of tetraodontiform fishes: a review focusing primarily on progress in the period from 1980 to 2014 . Ichthyological Research . 62 . 1. 72–113 . 10.1007/s10228-014-0444-5. free .