Which shark has a venomous spine on its dorsal fin?

The spiny dogfish has venomous spines in front of its dorsal fins. When threatened or handled, it can arch its back and drive a spine into a predator, while venom from the spine causes a painful sting.

Unlike many familiar sharks, the spiny dogfish has two dorsal fins and no anal fin. Each dorsal fin is preceded by a defensive spine, which explains both its common name and its reputation among fishermen. The species is usually identified by these spines, its slender body, and pale spots along the back.

The venom is generally described as mild to moderately painful rather than a weapon used to hunt. The spines are defensive structures, not teeth, and they are not unique to every shark. Blue, tiger, and bull sharks do not possess this characteristic venomous dorsal-spine system.

Spiny dogfish also have an unusual reproductive biology. Their gestation can last around 18 to 24 months, among the longest known for any animal, and they give birth to live young rather than releasing free eggs.