Swell Shark
Cephaloscyllium ventriosum

Physical Description

  • Sturdy, stout body into slender tail
  • Yellow-brown coloration with brown and white blotches to camouflage
  • Short, rounded snout with large mouth
  • Can grow up to 3 feet


  • Monterey, California to southern Mexico
  • Gulf of California, Mexico
  • The coast of Chile


  • Kelp forests with rocky substrates
  • Caves and shallow rock crevices
  • Most common in depths of 16 to 120 feet


  • Small fishes (both alive and dead), crustaceans, mollusks


  • Larger fish, some sharks, seals, sea lions

Interesting Facts

  • When threatened, the swell shark has an unusual response. It bends its body into a U-shape, grabs its tail fin in its mouth, and swallows a large quantity of sea water to swell to twice their usual size. This makes it hard for a predator to bite the swell shark or get it out of a crevice.
  • At night, swell sharks rest open-mouthed and let some prey get carried into their mouths by the currents.
  • Swell sharks lay large rectangular egg cases with curly tendrils on the corners that anchor the eggs to seaweed and rocks. The empty egg cases are often called “mermaids’ purses.” 
  • Though swell sharks look brown and white to the human eye, that is not how they look to each other. They live at depths where blue light is the most common, and it turns out their skin has pigment in it that biofluoresces, or absorbs that blue light and reflects it back as neon green; their eyes are also perfectly tuned to see this neon green pigmentation in each other, so they can easily find other swell sharks. The first work to determine this biofluorescence, done using an adapted camera that mimicked a swell shark’s eye, was done right in Scripps Canyon!

Sources: Monterey Bay Aquarium; Aquarium of the Pacific; National Geopraphic

Photo: Howard Hall

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