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Biological Profiles




CHAIN DOGFISH
Order - Carcharhiniformes
Family - Scyliorhinidae
Genus - Scyliorhinus
Species - retifer
chain dogfish

Taxonomy

Originally named Scyllium retifer by Garman in 1881, this name was quickly changed to the currently valid Scyliorhinus retifer (Garman, 1881). The genus Scyliorhinus comes from the Greek "skylla" meaning a kind of shark and "rhinos" meaning nose. There are no known synonyms used in previous scientific literature that refer to this species.

The family Scyliorhinidae is comprised of a large group of small, bottom-dwelling sharks often referred to as catsharks. Distinctive features of the catsharks include five pairs of gill openings, short broad pectoral fins, an anal fin, and large oval eyes.


Common Names

English language common names include chain dogfish, chain cat shark, and chain catshark. Other common names are alitán mallero (Spanish), kettingkathaai (Dutch), roussette maille (French) and syvännepunahai (Finnish). The common name "chain dogfish" is actually a misnomer as this shark belongs to a group referred to as catsharks.


Geographical Distribution

The chain dogfish occurs from Georges Bank, Massachusetts (U.S.) to Florida and from the northern Gulf of Mexico south to Nicaragua in the western Atlantic Ocean. It is especially abundant in the generally vicinity of the Chesapeake Bay, off the coast of Virginia. This species is absent from the Bahamas and the Antilles.


map
World distribution map for the chain dogfish


Habitat

As a demersal species, the chain dogfish resides in subtropical waters with temperatures from 47-52 °F (8.5 -11.3 °C). It is found along the outer continental shelf and upper slope. In the northern portion of its range, the chain dogfish lives at depths of 120-750 feet (36-230 m), while in its southern range it is found in waters deeper than 1,500 feet (460 m). The chain dogfish prefers structured habitats including rocky bottoms as well as living among man-made artifacts such as wires and cables.


Biology
Chain dogfish illustration
source Bigelow and Schroeder (1948) FNWA
· Distinctive Features
The chain dogfish is small with a slender body and wedge-shaped, blunt-tipped snout. The eye is narrow and somewhat oval in shape. The origin of the first dorsal fin is somewhat behind the free rear tips of the pelvic fins. The second dorsal fin is approximately half the size of the first dorsal. The pectoral fins are as broad as they are long with rounded corners. The outer margin is slightly convex and the distal margin is straight.

The anal fin is subtriangular with nearly straight edges and a rounded apex. The small caudal fin has a square tip or indented at the midline. The caudal fin also has a defined subterminal notch.


Chain dogfish
© George Burgess



· Coloration
The bold coloration of the chain dogfish distinguishes it from all other sharks. The body is reddish-brown along the back and a yellowish shade on the underside. There is a chain-like pattern of black or dark brown lines on the back and sides of the chain dogfish. This coloration pattern helps this species blend into its bottom habitat. The eyes are yellowish-green.


Chain dogfish dentition, A. Uper and lower teeth from center of mouth, B. Upper and lower teeth from sides of jaws near corners of the mouth
source Bigelow and Schroeder (1948) FNWA



· Dentition
The narrow teeth of the chain dogfish are triangular with smooth edges. There is a large central cusp with secondary cusps located on either side of each tooth. These teeth are similar in both the upper and lower jaws. The upper jaw has 21-26 teeth on each side of the symphysis. The symphysial teeth number 0-2. The lower jaw teeth number 20-22 on either side of the 0-4 symphysial teeth.


Chain dogfish denticles, including apical view
source Bigelow and Schroeder (1948) FNWA
· Denticles
The small denticles are narrow and flat. There are 3-5 ridges with the axial ridge most prominent. The anterior edge is either the posterior margin of the axial ridge or is notched between ridges. The surface of the skin feels smooth to the touch.


·Size, Age, and Growth
The largest male specimen caught measured 18.9 inches (48 cm) in length while the largest female measured 18.5 inches (47 cm) in length. At locations in the northern ranges of their distribution, maturation is thought to occur at smaller sizes than populations in the south. In the mid-Atlantic Bight, females mature at approximately 15 inches (38 cm) total length and males mature at 15.6 inches (39.5 cm). Age at maturation is approximately 8-9 years.

Growth rates of juvenile chain dogfish decrease exponentially with increasing body weight as they mature and reach maximum size.


Squid
courtesy National Undersea Research Center


· Food Habits
Chain dogfish feed on squid, small bony fishes, polychaete worms, and crustaceans. There is a dietary shift as sharks mature, with adults consuming more fish and fewer squid than juveniles do.


· Reproduction
Chain dogfish egg case, bottom
© George Burgess

The chain dogfish is oviparous or egg-laying. Follicles are ovulated in pairs upon reaching 18 mm in diameter. Each pregnant female releases two box-shaped egg cases after an unknown gestation period. Each egg case, also referred to as a mermaid's purse, measures about 2 inches long by 0.9 inches wide (6 cm x 2 cm) and has long stringy tendrils at each corner. The egg case is amber in color. Prior to release of the egg cases, the mother searches for bottom habitat with gorgonians and sponges or man-made structures for the tendrils to snag. These benthic invertebrates or structures provide an area to secure the egg cases. Adult chain dogfish often congregate in these nursery areas where females release egg cases. After the egg cases are released, there is no further parental involvement.

Developing chain dogfish embryo in egg case
© Jose Castro

Developing chain dogfish embryo removed from egg case
courtesy NOAA

The embryos are released from the egg case about 250 days later. The newborn pups have little protection from predators apart from their relatively inaccessible nursery ground. Upon hatching, each pup measures about 3.9 inches (10 cm) in length. In the Chesapeake Bay region, egg cases with developing embryos have been collected in February. This evidence has led biologists to believe that the young are produced during late winter and early spring in this location.

Juvenile chain dogfish
© George Burgess

Bottom trawlers often collect large numbers of juvenile chain dogfish in particular locations, leading scientists to believe that these nursery areas are highly localized in nature.


· Predators
Large piscivorous fishes are potential predators of the chain dogfish.


Importance to Humans

Large numbers of chain dogfish are taken as bycatch off the coast of Virginia near the Chesapeake Bay. This species is caught primarily by trawling in waters greater than 240 feet (73.2 m) and at temperatures of 50°F (10°C). At this time, there is little interest in this species as a fishery.

The chain dogfish is a popular aquaria display fish due to its small size.


Danger to Humans

Chain dogfish are considered harmless to humans due to their small size and small prey preference.

Chain dogfish in an aquarium
courtesy NOAA


Conservation

The chain dogfish is currently listed as a species of "Least Concern" with the World Conservation Union (IUCN). The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.


Prepared by:
Cathleen Bester