The dusky smooth-hound (Mustelus canis), also called the smooth dogfish or the dog shark, is a species of houndshark in the family Triakidae.
Taxonomy
M. canis can be known as smooth dogfish, Atlantic smooth dogfish, dusky smooth-hound, grayish, nurse shark, smooth dog, or smooth-hound. It was originally named Squalls canis. In Latin, mustelus translates to weasel and canis translates to dog. M. canis has an allopatric relationship with M. mustelus (common smooth-hound) and a sympatric relationship with M. norrisi (narrowfin smooth-hound).
Distribution and habitat
M. canis is found in marine and brackish waters and is demersal (bottom-dwelling) and oceanodromous (migratory in seas). They can be found between 42°N and 44°S and 100 and 46°W. M. canis in the North Atlantic migrates in response to changing temperature. In winter, they can be found in the Carolinas to the outlet of the Chesapeake Bay, and in summer from the mid-Atlantic to southern New England. They are most abundant on the East Coast, from Massachusetts to Florida, Brazil to Argentina, and in the Gulf of Mexico.
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Mustelus canis SI.jpg
Mustelus canis jaws.jpg|Jaws
Mustelus canis upper teeth.jpg|Upper teeth
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Dentition
One main characteristic of elasmobranch fishes is their ability to continually replace the teeth in their upper and lower jaws.
Diet
M. canis feeds mostly on crustaceans, polychaetes, and mollusks. Smooth dogfish also eat squid, worms, small fish, razor clams, and sometimes scavenge discarded animal products. They are nocturnal scavengers and opportunistic predators.
Juvenile females have filiform uteri, small ovaries with undifferentiated oocyctes, egg cells, and narrow, thread-like oviducts with undeveloped oviducal glands. Adolescents have enlarged oviducal glands with distinguishable oocytes and no or few corpora lutea. Adults have large ovaries and vitellogenic oocytes. Spermatozoa has been observed in preovulatory females. Tonic immobility is induced by grasping the first dorsal fin with one hand and the body immediately anterior to the anal fin with the other, inverting the shark and holding it rigidly. The mean time to induce tonic immobility in smooth dogfish was 32.5 seconds. The mean duration of the tonic immobility was 61.9 seconds. Sharks that had the "limp" response also exhibited tonic immobility. The "limp" response is a criterion for the onset of tonic immobility.