Like all species in the family Diodontidae, Long-spined Porcupinefish (Diodon holocanthus) can inflate themselves by swallowing water (or air). As in other species in the genus Diodon, this swelling causes the erection of the long movable spines covering the body. The Long-spined Porcupinefish is a robust fish with rounded dorsal and anal fins. Spines on the forehead of the Long-spined Porcupinefish are slightly shorter to much longer than are those immediately behind the pectoral fin base. Long-spined Porcupinefish have a broad dark bar through the eyes and, usually, four dark saddles on the back. The rest of the body is brownish yellow, paler below, with dark brown spots of moderate size (no spots on the fins beyond their bases). These spots are larger than the diameter of the spines. No spines are wholly on the caudal peduncle. Pelagic juveniles are around 6 to 9 cm. Maximum adult standard length (i.e., excluding tail) is around 30 cm, with a maximum total length of around 45 to 50 cm. In North American waters, the similar Spotted Porcupinefish (Diodon hystrix) is larger (to 91 cm), lacks the dark bars on the back and through the eyes, is covered with small dark spots that are around the same diameter as the spines, has the longest spines posterior to the pectoral fins, and has one or more spines wholly on the caudal peduncle.
The Long-spined Porcupinefish has a circumtropical distribution in the Atlantic, Pacific, and Indian Oceans (except that it seems to occur only peripherally on the Pacific Plate). It is found in the Atlantic from Florida and the Bahamas to Brazil and in the Pacific from the Gulf of California to Peru (see Leis 2006 for more details on geographic distribution).
Long-spined Porcupinefish are nocturnal and usually solitary. They feed on hard-shelled invertebrates. Larger individuals are found in a variety of benthic habitats from shallow reefs to open, soft bottoms to at least 100 m. In some areas, Long-spined Porcupinefish are harvested and dried in their inflated state for sale to tourists.
See Leis (2006) for a comprehensive key to identify the seven or eight genera and 18 or 19 species in the family Diodontidae that are recognized as valid by the author.
(Boschung et al. 1983; Eschmeyer and Herald 1983; Robins and Ray 1986; Leis 2003, 2006)