The term dogfish refers to sharks that belong to the order Squaliformes, especially the family Squalidae, that are found in many of the world's oceans. It's the common name for many of the 119 species of small to medium sized sharks that belong to this group. The most highly populated of the group is the spiny dogfish, which is one of the most abundant of any of the sharks. Dogfish have several shared characteristics including the arrangement of fins, bioluminescence, diet, and oviparous reproductive development.
Dogfish sharks are found in the most of the world's oceans, ranging from tropical to sub-arctic temperatures. They tend to stay in the cooler, lower depths most of the time, although they will travel to higher depths for short periods in cooler waters. Some species can also be found in coastal areas. In some areas, they are harvested for food and other uses, and many species are endangered due to this practice.
Dogfish sharks range in size depending on the species, from 19 inches (48 cm) to 5.2 feet (1.6 m) in length. Most species have rounded bodies, with the mouth located on the underside, slightly to the rear of the snout. The skin usually has a rough sand-papery feel, with five gill slits on each side of the head. There have two dorsal fins with spines on them but generally no anal fin; in many species, these spines are coated with venom, a feature unique to this type of shark. Many of the species have varying levels of bioluminescence, meaning that they appear to glow when they are in darker areas, as if they are lit from within.
Since most species are carnivorous, the diet of the dogfish shark usually consists of any readily available smaller animals. This can include invertebrates like jellyfish, crabs, krill, squid, and octopus or other fish like cod, herring, and haddock. One species, known also as the cookie cutter shark, actually carves out a chunk of flesh from its prey without eating the whole organism.
Reproductive development in the dogfish shark is oviparous. This means that the eggs develop inside the mother's body after fertilization by the male, and babies are born alive. During development, the babies are sustained by a yolk sac, and the mother shark gives birth after a gestation period of varying lengths, depending on the species. One species, the spiny dogfish, typically has the longest known gestation period lasting 18 to 22 months, and the average litter size is five to six babies known as pups.