Smooth Dogfish, Mustelus canis

Smooth Dogfish, Mustelus canis. Fish caught from a jetty in Cape May, New Jersey, August 2014. Length: 33 cm (13 inches). Catch, photograph and identification courtesy of Kenneth Tse, Toronto, Ontario, Canada.

Smooth Dogfish, Mustelus canis. Fish caught in the Cooper River, South Carolina, March 2011. Length: 36 cm (14 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.

The Smooth Dogfish, Mustelus canis, is a member of the Hound Shark or Triakidae Family, that is also known as the Dog Shark and the Dusky Smoothhound, and in Mexico as cazón dientón. Globally, there are twenty-two species in the genus Mustelus, of which eight are found in Mexican waters, three in the Atlantic and five in the Pacific Ocean. The Smooth Dogfish is scientifically interesting as it was the first shark to have documented viral infections.

The Smooth Dogfish has a small slender body. Dorsally they are an olive gray or brown in color with shades of yellow and gray-white transitioning to white ventrally. They do not have dorsal spots. They have the ability to change colors to match their backgrounds. Newborns have fins with light gray margins with the exception of the caudal fin which has a white margin. Their head has a tapering blunt snout, large oval cat-like eyes with a spiracle immediately behind, 5 gill slits, the last two of which are over the pectoral fins, and 10 rows of flat blunt teeth. These teeth are replaced at a rate of one row of teeth every 10 days. All of their fins are triangular shaped. The lower lobe of the caudal fin is rounded and much shorter than the upper lobe; the upper lobe has a deep notch near the tip. They have two dorsal fins, with the first being slightly larger than the second, and an inter-dorsal ridge. The second dorsal fin is about twice the size of the anal fin and is found slightly anterior to the anal fin. All of their fins lack spines. Adults males have fully developed claspers.

The Smooth Dogfish is considered to be one of the most abundant sharks on the east coast of the United States. They travel in large schools and are a common resident on continental shelves, bays, and other inshore waters and are normally found in shallow waters that are less than 18 m (60 feet) in depth but on occasion may be found in depths up to 200 m (660 feet). They are known to enter brackish waters. They are a demersal species and also a migratory species in response to changing temperatures, moving southward during the winter months. They reach a maximum of 1.52 m (6 feet 0 inches) in length and 12.2 kg (26 lbs 13 oz) in weight with females being larger than males. As of January 1, 2024, the International Game Fish Association world record stood at 17.01 kg (37 lbs 8 oz) with the fish caught in coastal waters off Cape May, New Jersey in June 2007. They are nocturnal scavengers and opportunistic predators that feed on large crustaceans (crabs, lobsters and shrimp), small fish (menhaden and tautog), and mollusks. In turn they are preyed upon by a wide variety of sharks including the Blacktip Shark, Carcharhinus limbatus, the Dusky Shark, Carcharhinus obscurus, and the Great Hammerhead, Sphyrna mokarran. Reproduction is viviparous with the embryo developing inside the body of the female from which it obtains nourishment from a yolk-sac placenta. Females have the ability to store sperm for up to a year. They have a gestation period of 10 to 11 months and litters can be between 4 and 20 pups. The pups are 34 cm (13 inches) to 39 cm (15 inches) at birth and arrive as miniature adults. The females have lifespans of up to 16 years; the males up to 10 years. The Smooth Dogfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Smooth Dogfish is a resident of all Mexican waters of the Atlantic that includes the Gulf of Mexico and the Caribbean.

The Smooth Dogfish is very similar to, and easily confused with the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (white spots on the back and sides), the Florida Smoothhound, Mustelus  norrisi (lower caudal lobe with a sharp point at the tip) and the Pacific Spiny Dogfish, Squalus acanthias (one spine before each dorsal fin).

From a conservation perspective the Smooth Dogfish is currently considered to be Near Threatened, due heavy fishing pressure with limited amounts of regulations. They have a late maturation, low fecundity, restricted distribution and are heavily fished commercially. They are a focus of commercial fishermen, utilizing gill nets, longlines and trawls with annual catch levers exceeding 500 tons (1,100,000 lbs) with the fish sold for human consumption. They are also pursued by recreational anglers as a sportsfish. They can also be found in large public aquariums. They have been utilized on a limited basis as a laboratory animal. This species is considered harmless to humans.