The spot-fin porcupinefish is a medium-sized fish which grows up to 91 cm, but the average size mostly observed is 40 cm.
Dorsal spines (total): 0; Dorsal soft rays (total): 14-17; Anal spines: 0; Anal soft rays: 14 - 16. Body robust; teeth united in each jaw but without a central division; body covered with long, sharp spines, folded backwards when body not inflated; 16 to 20 spines between snout and dorsal fin; dorsal region of caudal peduncle spiny; back, flanks and fins light brown with numerous dark spots; belly spiny. Spines long. Body grayish tan, with small black spots, but no large dark blotches. Belly white, surrounded by dusky ring. About 20 spines in an approximate row between snout and dorsal fin. Its body is elongated with a spherical head with big round protruding eyes, a large mouth rarely closed. The pectoral fins are large, the pelvic fins are absent, the anal and dorsal fins are close to the caudal peduncle. The latter move simultaneously during swimming. The skin is smooth and firm, the scales are modified into spines. The body coloration is beige to sandy-yellow marbled with dark blotches and dotted with numerous small black spots. In case of danger, the porcupinefish can inflate itself by swallowing water to deter the potential predator with its larger volume and it can raise its spines.
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Adults generally linger inshore, around areas that offer shelter, such as caves, shipwrecks, reefs, and ledges. They are nocturnal and solitary creatures, commonly residing in holes and crevices within the reef complex. Juveniles are pelagic until reaching 8 inches (20cm) in length, after which they become benthic.
Spot-fin porcupinefish are nocturnal predators, with strong jaws for feeding on snails, hermit crabs, and sea urchins. Just as some birds are able to crack open nuts with their strong beak, the porcupinefish can crack open the external skeleton of a sea urchin with its strong beak-like mouth.
Its wide distribution may be attributed to the pelagic, or open ocean, stage of the eggs and larvae. The eggs are spherical, drift with the current, and hatch after about five days. Early planktonic larvae have large amounts of yolk still present, lack a functional mouth, and have not developed full eye pigmentation. It takes a few days for the yolk to be used up and for the body to develop to where the larvae truly resemble fish. Pelagic juveniles are often associated with large clumps of floating seaweeds called sargassum, and are often consumed by dolphin (mahi mahi) and billfishes. The duration of this pelagic stage is unknown, but at some point the juveniles travel to shallower waters to become adults.
Spot-fin porcupinefish is collected for private and public show aquariums.