CHAIN CATSHARK OR CHAIN DOGFISH
This shark has properties that allow it to fluoresce
The Chain catshark or Chain dogfish (Scyliorhinus retifer) is a small catshark belonging to the family Scyliorhinidae. This catshark is quite common among its range in the northwest Atlantic, Gulf of Mexico and Caribbean, and can be distinguished by its reticulated pattern and its unique biofluorescent property.
Family: Scyliorhinidae – Catsharks
Common Name– Ground Sharks
Common Name– Catsharks
Average Size and Length: Each egg case measures around 2.7 x 6.5 cm. Hatchlings measure around 10-11 cm/3.9-4.3 inches. Mature males have been measured between 38-50 cm/1.2-1.6 feet and mature females between 35-52 cm/1.1-1.7 feet. The maximum recorded has been 59 cm/1.9 feet. Young reach between 25-30 cm/9.8-11.8 inches in 2 years in captivity.
Teeth and Jaw: It has well developed labial furrows. The teeth are narrow, triangular and have smooth edges. There is a large central cusp with two, surrounding secondary cuspslets 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.
Head: The snout is round, wedge-shaped and blunt. The eyes are yellowish-green in color, cat-like, large and oval.
Denticles: The dermal denticles are small, narrow and flat, giving the shark a smooth texture. 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.
Tail: They have an asymmetrical, sub-terminal, notched caudal fin. It has a square tip that is indented at the midline.
Demographic, Distribution, Habitat, Environment and Range: The Chain catshark or Chain dogfish is found in the northwest Atlantic Ocean, the Gulf of Mexico and Caribbean in the USA. It has been found from Georges Bank, Massachusetts, to Florida and Texas. In Mexico, it has been found in the Campeche Gulf, and in the Barbados area between Jamaica, Honduras and Nicaragua (45°N – 15°N, 99°W – 64°W). They are considered demersal subtropical. It is found on the outer continental shelf and upper slope on or near the bottom between 240-2,474 feet. It has been found deeper in the south. Specifically, in the northern part of its range it is mainly found between 118-755 feet and in the southern areas generally deeper than 1,509 feet. Due to the shark’s depth distribution, it more than likely does not participate in any large-scale migration. It may be most common among rough, rocky untrawlable areas, which make great places to lay eggs.
Temperature is thought to limit the Chain catshark’s distribution in northern areas, particularly during the winter. Although bands of warm water at the edge of the shelf have been observed, the temperature varies seasonally. In general, the Chain catshark is found in waters with a temperature between 47 °F and 57 °F.
Diet: They feed on squid, bony fish, crustaceans, and polychaetes.
Aesthetic Identification: The Chain catshark or Chain dogfish has a black chain pattering outlining faint dusky saddles. There are no spots. This pattern is unique to this species as well as the Reticulated swellshark. The body is slender in shape. The dorsal fins are set far back and are somewhat lobed. 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 fin. 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 has almost straight edges with a rounded apex, and it is subtriangular.
Biology and Reproduction: They are oviparous. The eggs are laid in pairs every 8-15 days in captivity during the spring and summer. They lay 44-52 eggs per year. The females will wrap the tendrils (that are up to 35 cm long) of the egg cases around seabed projections such as corals. Egg cases found in the oviduct are soft, pale yellow and translucent. When deposited, they become hardened and become dark amber with white bands.
Each egg case hatches after about 7 months in captivity between 53-55 degrees F. This could be longer in nursery areas, and at temperatures reaching as low as 45 degrees F. Generally, though, embryos take 8–12 months to develop due to temperature variations in the environment. According to Castro, Bubucis, and Overstrom (1988), a typical developmental timeline of the embryo is as follows:
10 mm (0.4 in) – it has well-defined gill arches and has a thin ventral fin-fold
21 mm (0.8 in) – dorsal and pelvic fin buds appear
33 mm (1.3 in) – embryo has protruding eyes and well-developed gill filaments
43 mm (1.7 in) – it has lost its translucency and develops slits in the egg case, allowing fluid exchange from surrounding seawater and the interior
58 mm (2.3 in) – the fin-fold starts to decay
66 mm (2.6 in) – the fin-fold and gill filaments are reduced or absent
74 mm (2.9 in) – external appearance is complete, but yolk sac is still being absorbed
100–110 mm (3.9–4.3 in) – hatching
In the female Chain catshark, follicle development has been correlated to nidamental gland size. They are considered mature when they have a fully developed nidamental gland or shell gland. This is marked by the gland’s growth to 1.8 cm or more in width. Sexual maturity in the female is seen at 52 cm/1.7 feet in length under normal conditions. There has been evidence however that some northern populations of the shark may mature at a smaller size, at 41 cm/1.3 feet. In the male Chain catshark, testis development is correlated to clasper size, and maturity is marked when it develops hardened claspers that are 3 cm/1.2 inches or more in length. Males reach maturity at a length between 37-50 cm/1.2–1.6 feet. (Castro, Jose I.; Bubucis, Patricia M. & Overstrom, Neal A. (1988). “The Reproductive Biology of the Chain Dogfish, Scyliorhinus retifer“. Copeia. 3: 740–746).
The female Chain catshark is able to store sperm and lay eggs several days after initial copulation. The shark has been known to store sperm up to 843 days although, there are some circumstances of poor egg development in eggs laid later. It is suggested that this could be due to a number of factors including, senescence, low sperm viability, or water quality factors. (Castro, Jose I.; Bubucis, Patricia M. & Overstrom, Neal A. (1988). “The Reproductive Biology of the Chain Dogfish, Scyliorhinus retifer“. Copeia. 3: 740–746).
The Chain catshark is one of only a few elasmobranch species shown to possesses bioluminescent fluorescent properties. The researchers of the study examined the vision of the Chain catshark using microspectrophotometry and designed a “shark-eye” camera that yielded contrast information on areas where fluorescence is anatomically distributed on the shark. The repeated evolution of biofluorescence in elasmobranchs, coupled with a visual adaptation to detect it; and evidence that biofluorescence creates greater luminosity contrast with the surrounding background, highlights the potential importance of biofluorescence in elasmobranch behavior and biology. The key fluorescent pigments in the Chain catshark and the Swellshark are a set of brominated kynurenine compounds that appear to be synthesized by the kynurenine pathway starting from 6-bromo-tryptophan. The biochemical origin of 6-bromo-tryptophan in these species is not known. Read more of Dr. Gruber’s research here in our PSD Glow in the Dark Sharks article, and his findings in this publication as well. (Gruber, David F.; Loew, Ellis R.; Deheyn, Dimitri D.; Akkaynak, Derya; Gaffney, Jean P.; Smith, W. Leo; Davis, Matthew P.; Stern, Jennifer H.; Pieribone, Vincent A.; Sparks, John S. (2016). “Biofluorescence in Catsharks (Scyliorhinidae): Fundamental Description and Relevance for Elasmobranch Visual Ecology“).
Behavioral Traits, Sensing and Intelligence: They are known to swallow pebbles for counterweight. When the females wrap the tendrils around corals, they use a special rapid circular swimming technique to do so. The egg cases are secured on vertical structures.
They typically spend the day resting on the bottom. In aquaria, they are relatively motionless, spending the day resting on the bottom, but during the night and when fed they are very active. It has been observed with large burrowing cerianthid anemone tubes and boulders. Its pattern suggests that bottom rubble is used as camouflage. Adult sharks tend to prefer rough bottoms, while the immature sharks are found near smoother regions.
Observed mating between the species suggests biting plays an element and that mating occurs repeatedly. Behavioral observations include the male biting the female until it can get a firm grasp and subsequently wraps its body around the female for copulation. After copulation, the male releases his bite and both separate.
Speed: They are sluggish in nature and are commonly found resting on the bottom.
Chain Catshark or Chain Dogfish Future and Conservation: They are currently of least concern. They are quite common among its range. They are commonly caught for cold water aquaria because of its small size and beautiful pattern. They are also commonly studied in laboratories.
Chain Catshark or Chain Dogfish Recorded Attacks on Humans: Not a threat to humans.