The ever-grumpy looking spot-fin porcupine fish is one of the “top spots” on any dive. With bizarre group-mating habits and a hilarious defensive mechanism, the spot-fin porcupinefish is our Wildlife of the Week:

Species: Diodon hystrix

Class: Actinopterygii

Status: Least Concern 

Diet: Sea urchins and hard-shelled molluscs

Size: Up to 91 centimetres in length

Weight: Up to 2.8 kilograms

Life span: 10 years in the wild

Behaviour: Typically solitary, outside of breeding, and are nocturnal, hiding during daylight hours

Distribution: Nearctic, Ethiopian, Australian, Oceanic islands, Indian Ocean, Atlantic Ocean, Pacific Ocean, Mediterranean Sea

Ecosystem: Adults are generally found in holes and crevices in inshore areas, including lagoons, caves, shipwrecks, reefs, and ledges, and are also found in seamount areas. They are found at depths up to 50 metres, most commonly between 3 and 20 metres.

5 fast facts: 

  • When threatened, they inflate their bodies by swallowing water. Their integument (the protective outer layer) is very flexible, allowing expansion of the body up to three times its original size. When no longer threatened, excess water is expelled and the fish returns to its normal size.
  • Their eggs are buoyant, pelagic, spherical, and 1.9-2.1 millimetres in diameter. About five days after fertilisation, eggs hatch, and larvae, which average 2.6 millimetres in length, float in the open ocean near the surface.
  • Breeding begins when water temperatures reach approximately 25°C, likely from May through August. Multiple males approach a female at a time, bringing her up to the surface of the water, where, if she has ripe eggs, she will release them. All of the males (usually 4-5) contribute sperm.
  • As in other bony fishes, spot-fin porcupinefish use their eyes to see, nares to sense dissolved chemicals, and a lateral line to detect vibrations and movement via changes in water pressure.
  • Spot-fin porcupinefish are an intermediate link in the reef food chain, serving both as nonspecific predators of benthic (bottom-dwelling) invertebrates and as prey for higher-order predators. Like other fish, this species is host to numerous endo- and ectoparasites (living inside and on the outside of the host, respectively).