Featured Species Friday: Swellshark (Cephaloscyllium ventriosum)

This week’s Featured Species is one of the largest catsharks and is named for a interesting self defense mechanism that allows this shark to puff its self up to nearly double its resting body size (Frederico & Hassall, 1998; Skomal, 2016). The Swell Shark (Cephaloscyllium ventriosum) is found in kelp beds and rocky sea bottoms in the Eastern Pacific Ocean along the coastal United States, Baja Mexico, and South America, where it spends most of its time resting in caves and rocky crevices during the day and venturing out to hunt at night (Skomal, 2016).

California Swell Shark 011
Murch, A. (Photographer). (n.d.). Swell Shark in Kelp Bed [Digital Image]. Retrieved from http://www.elasmodiver.com/


Swell sharks are a member of the Scyliorhinidae family, the catsharks, which is one of the largest families of sharks with over 160 species in 17 genera (Parker, 2008). The swell shark (picture below, cuddled under the horn shark) are known for their saddle-like brown spots over a cream or sandy background, with a broadly rounded snout, large dermal denticles that can be seen with the naked eye, and cat-like eyes (Tricas, et al., 1997; Parker, 2008). They also have over 60 small teeth per jaw with extremely sharp long central cusps and two smaller cusplets on either side that are ideally suited for nabbing small fishes and invertebrates (Parker, 2008).

Flannery, A.. (Photographer). (2016 April 13). Swell shark (botom) and Horn shark (top) have a cuddle [Digital Image].

As I mentioned, the swell shark is named for its incredible ability puff up when threatened. In 1947, Eugenie Clark, later to be known as the shark lady, studied the inflating mechanism of these sharks for her Masters work (Clark, 1947). She found that, much like the puffer fishes of Tetraodontidae and Diodontidae, the swell shark has puffs up by swallowing water or air down into its stomach and is held inside the cardiac stomach by a strong esophageal sphincter (Clark, 1947). So when the swell shark is threatened by predator, it can swallow enough water – or if near the surface, air – to swell its belly to double its size, wedging its body into rocky crevices, making it difficult to remove and potentially too large to swallow (Skomal, 2016).

Swollen swell shark provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur [Digital Image]. (2009). Retrieved from https://www.mexican-fish.com/swell-shark/



Swell sharks are oviparous, which means they are egg laying sharks. Females are capable of laying 2 eggs at a time, 1 from each oviduct (Ebert, 2003). However, it is unknown how often females are able to lay eggs when not in human care, so their fecundity has yet to be determined and is thought to be low (Ebert, 2003). Their eggs are flat and rectangular with long horns extending outward and inward from each corner. These horns help to secure the eggs to the rocky sea bottom or kelp beds by entangling in the surrounding environments (Skomal, 2016). These rectangular shark eggs are sometimes referred to as mermaid purses. After 7 to 10 months – depending on the water temperature – the fully developed 5 to 6 inch (13 to 15 cm) young are ready to hatch from their cases (Parker, 2008).

Four stages in the development of the swellshark. A. Eggs are laid in greenish-amber cases known as “mermaid’s purses” and take 7 to 10 months to hatch. B. The large yolk sac is gradually reduced as the developing embryo uses its contents; by the time the shark is ready to hatch, the yolk has completely or almost disappeared. C. The hatchling has a double row of enlarged denticles along its back that apparently at as an “anti-slip” ratchet to help it force its way out of the egg case. D. Newly hatched sharks are active, can swim strongly and are ready to search for food. (Stevens, 1997).


Watch the amazing rescue, care, and birth of a swell shark in its egg case!

GoodSirEric. (2011 October 3). Swell Shark Egg Lifecycle and Hatching [Video Clip]. Retrieved from https://www.youtube.com/


Another amazing trait of many species of catsharks, including the swell shark, is biofluorescence. Under normal lighting conditions, the swell shark does not appear to glow to the naked human eyes. However, under specific lighting conditions, the skin of the swell shark can glow neon green. Biofluorescence the process in which  organisms absorb light, transform it, and eject it as a different color. This is different from bio-luminescence where organisms are producing and emitting their own light. Not much is known about their biofluorescent abilities or what purpose they may serve the sharks just yet, but it an exciting realm of study that I am looking forward to seeing results from, hopefully in the next few years!

Discovery. (2015 July 8). The Neon Green Swell Shark [Video Clip]. Retrieved from https://www.youtube.com/watch?v=_FaGrEGJmTY


Shark Stats

Authority: Garman, 1884

Family: Scyliorhinidae; approximately 160 species

Length: Up to 3 feet (0.9 m)

Weight: On average between 10 – 20 lb (4.5 – 9 kg)

Habitat: Coastal waters in kelp beds and rocky bottoms

Depth: Commonly found around 100 feet (30.48 m), sometimes as much as 1,500 feet (457.2 m)

Reproduction: Oviparous

Gestation: Egg cases take 7.5 – 10 months to hatch

Litter Range: Females produce 1 egg case per oviduct at a time; Annual egg production is unknown

Home Range: Eastern Pacific Ocean

Diet: Bottom fishes and invertebrates

IUCN Status: Least Concern

(Ebert, 2003; Parker, 2008; Villavicencio-Garayzar,  White, & Lowe, 2015; Skomal, 2016)

Thanks for reading about the incredible swell shark this week. If you missed last week’s elusive Megamouth shark, be sure you check it out! If you have a species of elasmobranch you’d love to see featured, please send me a message or leave me a comment! I’d love to know what you’d like to know more about!

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.


Featured Image Source

Thundafunda (Photographer). (2009 June 6). Swellshark [Digital Image]. Retrieved from https://www.flickr.com/

Literature Cited

Clark, E. (1947). Notes on the inflating power of the swell shark, Cephaloscyllium uter. Copeia1947(4), 278-280.

Ebert, D. (2003). Sharks, rays, and chimaeras of California(No. 71). Univ of California Press.

Frederico, L., & Hassall, G. (Eds.). (1998). Reader’s Digest Explores: Sharks (1st ed.). Reader’s Digest.

Gruber, D. F., Loew, E. R., Deheyn, D. D., Akkaynak, D., Gaffney, J. P., Smith, W. L., … & Sparks, J. S. (2016). Biofluorescence in Catsharks (Scyliorhinidae): fundamental description and relevance for elasmobranch visual ecology. Scientific reports6, 24751.

Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Stevens, J. D. (Ed.). (1997). Sharks (6th ed.). New York: Facts on File.

Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

Villavicencio-Garayzar, C.J., White, C.F. & Lowe, C.G. 2015. Cephaloscyllium ventriosum. The IUCN Red List of Threatened Species 2015: e.T60227A80671800. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T60227A80671800.en

Next Post

Featured Species: Broadnose Sevengill Shark (Notorynchus cepedianus)

Previous Post

Featured Species Friday: Megamouth Shark (Megachasma pelagios)


Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Powered by WordPress.com.

Up ↑

%d bloggers like this: