Porcupine Fish: ID, Size, Toxin and vs Pufferfish

A porcupine fish is a solitary, round-bodied reef fish covered in long spines that stand up when it swallows water and inflates. The family, Diodontidae, has about 18 species in 7 genera (Wikipedia). The common Diodon hystrix reaches 36 inches, is usually seen at around 16 inches, and hides in caves, ledges, reefs and wrecks by day before hunting snails, urchins and hermit crabs at night (Florida Museum).

No, but they are close relatives in the same order, and both inflate. The differences:

• Spines: porcupinefish have real spines, modified scales that lie flat until the fish inflates; pufferfish have no spines, at most short prickly bumps (Seattle Aquarium)
• Teeth: adult pufferfish have fused front teeth forming a beak; porcupinefish have one strong bite plate in each jaw (Seattle Aquarium).
• Family: porcupinefish are Diodontidae; the fish usually called pufferfish are Tetraodontidae (Wikipedia)

See our puffer fish page for the other side of the comparison.

In the Atlantic the closest look-alike is the balloonfish, Diodon holocanthus. The Florida Museum's test is the spotting:

• Porcupinefish (D. hystrix): grey-tan body evenly speckled with small black spots, including on the fins, and a white belly; about 20 spines between the snout and the dorsal fin
• Balloonfish (D. holocanthus): larger spots or dark blotches on the body only, not on the fins

A photo that shows the fins clearly is enough to separate them.

Yes. Like pufferfish, porcupinefish carry tetrodotoxin in internal organs such as the liver and ovaries; Wikipedia describes it as at least 1,200 times more potent than cyanide and says the toxin comes from bacteria in the fish's diet. The Florida Museum adds that the fish secretes a toxic substance from its skin and is 'usually considered poisonous'. The Seattle Aquarium notes that tetrodotoxin can sicken or kill most predators.

Do not handle a live one with bare hands, and never try to make it inflate: the Seattle Aquarium explains that inflating stretches the skin painfully and puffers must stretch their muscles first to avoid injury. If anyone has eaten porcupinefish or pufferfish and feels numbness or tingling around the mouth, weakness or trouble breathing, call your local emergency number or poison control centre at once.

Treat it as not edible. It is eaten in a few places despite the risk: Wikipedia records it as an exotic food called tagotongan in Cebu, Philippines, and the Florida Museum says it was historically eaten in Hawaii and Tahiti. Both sources describe the tetrodotoxin risk, and there is no reliable way for a home cook to tell whether a particular fish is safe. If anyone has eaten porcupinefish or pufferfish and feels numbness or tingling around the mouth, weakness or trouble breathing, call your local emergency number or poison control centre at once.

The Florida Museum gives up to 36 inches for Diodon hystrix, with adults usually around 16 inches; juveniles drift in open water until about 8 inches, then settle on the bottom. On inflation the sources differ: Wikipedia says the fish nearly doubles in size, while the Seattle Aquarium says puffers and porcupinefish reach two or three times their normal size.

Spines and toxin do not make them safe from everything: dolphinfish, wahoo and sharks eat adults (Florida Museum), and Wikipedia adds orcas for adults and tuna, dolphins and mantis shrimp for juveniles. Some are collected for public and private aquariums, and dried, inflated porcupinefish are sold as tourist novelties (Florida Museum).