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Characteristics, distribution and ecology
Taxonomische classification
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Author: (Garman, 1880)

Field Marks:
A large variegated catshark, with small dark and light spots, undersides spotted, no labial furrows, second dorsal smaller than first, anterior nasal flaps reaching mouth.

Diagnostic Features:
Snout broadly rounded-angular in dorsoventral view, extremely short; anterior nasal flaps broadly lobate or subtriangular, overlapping mouth posteriorly. Claspers short and stout. Colour pattern of variegated dark brown blotches and saddles and numerous dark and some light spots on a yellow-brown background on body and fins, underside of head and abdomen spotted; fins without conspicuous light margins. A large species (see size below).

Geographical Distribution:
Eastern Pacific: Central Californiai (Monterey Bay) to Gulf of California and southern Mexico; central Chile.

Habitat and Biology:
A sluggish, nocturnal benthic and epibenthic shark of warm-temperate and subtropical continental waters, on the continental shelves and upper slopes, with a depth range from, inshore to 457 m, commonest at depths of 5 to 37 m. This species prefers rocky, algal-covered areas of kelp beds, but also occurs on algal-covered bottom without kelp. The swell shark usually spends the day Iying on the bottom motionless in rocky caves and crevices but becomes active at night and swims slowly through bottom algae or in open water close to the bottom. Swellsharks may occur in aggregations 2 of several individuals while resting, sometimes piled atop one another. This is a hardy species in captivity, and will live in tanks for several years. Under experimental conditions this species was shown to have an 4 endogenous, circadian activity pattern that is clearly calibrated by diel changes in light.

The swellshark is oviparous and lays its eggs in large, greenish-amber, purse-shaped egg-cases, which hatch in 7.5 to 10 months depending on water temperature; the young hatch at 13 to 15 cm long. These have a double row of enlarged denticles down the back that apparently are used as an antislip rachet to aid the young to force their way out of their egg-case. Females will lay eggs in captivity.

This shark feeds on bony fishes, alive and dead, and probably crustaceans. It is hypothesized that the nocturnal activity pattern of this sluggish, slow and weak-swimming shark aids in capture of its prey. The swellshark has a huge mouth and relatively small, sharp-pointed holding teeth that can handle large prey, but the shark itself seems incapable of dashing after active prey and may specialize in catching day-active bony fishes that lie on the bottom at night and are relatively inactive and unresponsive.

This shark, like at least most others in the genus and like porcupine fishes (Diodontidae) and puffers (Tetradontidae, etc.), can greatly inflate its stomach like a balloon when disturbed or harassed, with water or air. It can expand its stomach while in a crevice, wedging itself in and making it very difficult to extract. It is harmless to people, but may bite when harassed.

Maximum size at least 100 cm, adult males 82 to 85 cm, size at hatching 14 to 15 cm.

Interest to Fisheries:
None at present, occasionally caught by sportsfishers and divers but probably not utilized.

Kato, Springer and Wagner (1967) and Springer (1979) synonymized the swellsharks of the eastern North and South Pacific (C. uter and C. ventriosum), which is followed here.

Type material:
Holotype: Museum of Comparative Zoology, Harvard, 740 mm adult female. Type Locality: Valparaiso, Chile.

Swellshark (Cephaloscyllium ventriosum)