PORCUPINEFISH
DIODONTIDAE
Balloonfish
Diodon holocanthus
    Ecological Descriptors
Habitat Size (cm) Diet Behaviour Sex 
Dem (Co, R, S, M) 50 Mol, Ech, Cru I, Sh F
 
 
General:
Although confused by some with Pufferfish (Tetrodontidae [="four teeth"]), Porcupinefish (Diodontidae [="two teeth"]),  differ in their beak-like teeth are fully fused, lacking a noticable groove and have obvious spines on the body. Both families have the ability to enlarge themselves as a predator deterrent.

Description
:
Body with a truncated
head with long spines. Body is olive to brown. A dusky vertical band runs through eyes, dusky blotches or bands may be present on the back. Iris yellow, pupil with iridescent blue-green specks/ lines. Head and body with long spines. Spines usually lowered, but may become erect without inflating the body. Often with small dark spots on the body, no spots on the fins

Ecology
This is a demersal,  reef-associated species that is usually found between 2-15 m (but down to 100m). It occurs over open muddy substrates and rich soft bottoms, as well as around coral reefs. Juveniles (6-9cm) are often found with floating Sargassum rafts. Young individuals and sub-adults sometimes form small groups. It feeds at night on molluscs, sea urchins, hermit crabs, and other crab species. It is a relatively poor swimmer, using mainly the pectoral, anal and dorsal fin. Unconfirmed whether this species is toxic.
The iridescence in the corneas resembles that of several other fish with colouration created by stacks of multiple layers of connective tissue or collagen fibrils. These plates provide constructive interference and reflect a specific wavelength of light, and are particularly effective when the angle of incidence of light is oblique as bright downwelling sunlight would appear in a shallow reef. These reflected rays have a characteristic multicoloured appearance because only a restricted band of wavelengths is reflected for any single viewing angle. In the fish that have been studied, it has been calculated that the iridescent layer provides a significant increase in the visual range under water without sacrificing sensitivity.
Balloonfish
Synonyms:
Longspine balloonfish
(C) Dr P Ryan/ RyanPhotographic
Balloonfish
240
POISONOUS
(C) John Easley