The chain catshark or chain dogfish (''Scyliorhinus retifer'') is a small, reticulated catshark that is biofluorescent. The species is common in the Northwest Atlantic,

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, and

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

. It is harmless and rarely encountered by humans. It has very similar reproductive traits to the small-spotted catshark (''S. canicula'').

Distribution

The chain catshark is found in the Northwest Atlantic,

and

, ranging from George's Bank in

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

, to

Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...

and

Barbados Barbados, officially the Republic of Barbados, is an island country in the Atlantic Ocean. It is part of the Lesser Antilles of the West Indies and the easternmost island of the Caribbean region. It lies on the boundary of the South American ...

. In the Mid-Atlantic Bight, the chain catshark is found along the outer

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

and upper slope. The shark occupies depths of ; in the northern part of its range it is mainly found between and in the southern areas generally deeper than . Due to the shark's depth distribution, it has been suggested that the shark does not perform large-scale migrations. Temperature is thought to limit the shark'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, thus limiting this non-migratory species. In general, the chain catshark is found in waters with a temperature between and . Scyliorhinus retifer jaws.jpg, Jaws Scyliorhinus retifer upper teeth.jpg, Upper teeth Scyliorhinus retifer lower teeth.jpg, Lower teeth

Habitat and behavior

The catshark spends the daytime resting at the bottom, usually in contact with certain structures. It has been observed with large burrowing cerianthid anemone tubes and boulders. The bottom rubble is thought to be used as a camouflage with the shark's spotted surface. Adult sharks tend to prefer rough bottoms, creating a difficulty for trawl sampling, while the immature forms are found near smoother regions. The chain catshark has been known to feed on squid, bony fish,

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...

and crustaceans. In aquaria, they are relatively motionless, spending the day resting on the bottom, but during the night and when fed they are very active.

Reproduction

Size and sexual maturity

The maximum length of this shark is . In the female chain catshark, follicle development has been correlated to

nidamental gland Nidamental glands are internal organs found in some elasmobranchs and certain molluscs, including cephalopods (specifically Decapodiformes and nautiluses) and gastropod Gastropods (), commonly known as slugs and snails, belong to a large Ta ...

size, thus, they are considered mature when they have a fully developed nidamental gland or shell gland. This is marked by the gland's growth to or more in width. Sexual maturity in the female is seen at in length under normal conditions. There has been evidence however that some northern populations of the shark may mature at a smaller size, at . In the male catshark, testis development is correlated to clasper size, thus maturity is marked when it develops hardened claspers that are or more in length. Males reach maturity at a length between .

Mating

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.

Egg-laying

The chain catshark prefers vertical structures for egg deposition and always deposits eggs in pairs. The interval between pairs of eggs ranges from a few minutes to 8 days. Development rates average 1 mm diameter per 7.7 days although temperature has also been seen to affect follicle development.

Sperm storage and egg cases

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 Senescence () or biological aging is the gradual deterioration of Function (biology), functional characteristics in living organisms. Whole organism senescence involves an increase in mortality rate, death rates or a decrease in fecundity with ...

, low sperm viability, or water quality factors. Egg cases found in the oviduct are soft, pale yellow and translucent. They also feature two coiled tendrils, a key adaptation which allows snagging on rocks or man made structures, providing grounding and safety. When deposited, they become hardened and become dark amber with white bands.

Embryos

Embryos take 8–12 months to develop due to temperature variations in the environment. The catshark lays eggs in their

blastodisc The blastodisc, also called the germinal disc, is the embryo-forming part on the yolk of the egg of an animal that undergoes discoidal meroblastic cleavage. Discoidal cleavage occurs in those animals with a large proportion of yolk in their eggs ...

form. The following exhibits a typical developmental timeline (measurements are embryo length): * – it has well-defined gill arches and has a thin ventral finfold * – dorsal and pelvic fin buds appear * – embryo has protruding eyes and well-developed gill filaments * – it has lost its translucency and develops slits in the egg case, allowing fluid exchange from surrounding seawater and the interior * – the finfold starts to decay * – the finfold and gill filaments are reduced or absent * – external appearance is complete but

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

is still being absorbed * – hatching

Fluorescence

The chain catshark is one of four

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

species shown to possesses biofluorescent properties. The researchers of the study examined the vision of ''Scyliorhinus retifer'' 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 swell shark are a set of brominated

kynurenine -Kynurenine is a metabolite of the amino acid -tryptophan used in the production of niacin. Kynurenine is synthesized by the enzyme tryptophan dioxygenase, which is made primarily but not exclusively in the liver, and indoleamine 2,3-dioxygena ...

compounds that appear to be synthesized by the kynurenine pathway starting from 6-bromo-

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...

. The biochemical origin of 6-bromo-tryptophan in these species is not known.

Relationship with humans

The chain catshark is not currently fished for human consumption. The chain catshark has been described as "gorgeous", and this, combined with its small size, makes it a popular cold-water aquarium fish. It is frequently displayed and bred at

public aquarium A public aquarium () or public water zoo is the aquatic counterpart of a zoo, which houses living aquatic animal and aquatic plant, plant specimens for public viewing. Most public aquariums feature tanks larger than those kept by home aquarists, ...

s. Research in shark behavior, including reproduction, has been done in chain catsharks kept in public aquariums or laboratories.