Spotted Porcupinefish

Diodon hystrix is a species of marine fish in the family Diodontidae.

Description

The spot-fin porcupinefish is a medium-sized fish which grows up to 91 cm, but the average size mostly observed is 40 cm. 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.

The porcupinefish concentrates a poison, called tetrodotoxin, in certain parts of its body such as the liver, skin, gonads and the viscera. Tetrodotoxin is a powerful neurotoxin. This defensive system constitutes an additional device to dissuade the potential predators.

Distribution & habitat

The porcupinefish is found in all the tropical and subtropical waters of the world, including the Mediterranean Sea.

Juveniles are pelagic up to the time that they are about 20 cm in length. Adults favour lagoons, top reefs and seaward coral or rocky reefs from one to 50 m depth, sheltering under ledges or in caves during the day.

Fun facts

• Porcupinefish possess an incredible ability to move their eyes independently and are often observed swimming away from divers at an angle, keeping one eye on them the entire time.
• One of the few natural predators of porcupinefish is the dolphin. Scientists believe that the stress of this experience causes the fish to release their toxin, which may have an addictive effect on the dolphins. Observations have shown dolphins engaging in a game resembling underwater volleyball with these fish.
• In the waters of the Gulf of Thailand near Koh Tao, you’ll find the island’s most famous resident – Steve, the porcupinefish! The friendliest fish in the sea and the ultimate dive buddy. But remember: look, don’t touch! Like all porcupinefish, Steve is toxic, so it’s best to admire him from a safe distance.

Feeding

The porcupinefish's diet is based on Sea urchins, gastropods and crustaceans.

Behavior

This fish is solitary, except during mating periods, it has a nocturnal activity with a maximal activity at sunset and sunrise.

Parasites

As most fish, the porcupinefish is infected by a variety of parasites. Spectacular parasites are the cysts of the larvae of the trypanorhynch cestode Molicola horridus, often found in great numbers in the liver. These parasites are not appetizing, but represent no danger to humans.