The inflatable fluorescent shark: GLOWING BALLOON!

The Swellshark (Cephaloscyllium ventriosum) is a catshark belonging to the family Scyliorhinidae. Swellsharks can be found in the eastern Pacific between central California and to southern Mexico, with an additional population off the coast of Chile. As a defense, the Swellshark is able to expand to approximately double its regular size by swallowing water (or air on land). Swellsharks are florescent. Read about it here in the PSD Glow in the Dark Sharks.


Family: Scyliorhinidae – Catsharks

Genus: Cephaloscyllium 

Species: ventriosum


Phylum– Chordata

Class– Chondrichthyles


Common NameGround Sharks

Family– Scyliorhinidae

Common NameCatsharks




Average Size and Length: Hatchlings measure between 13-15 cm/5-5.9 inches. Adult males measure between 82-85 cm/2.7-2.8 feet. The maximum recorded is over 100 cm.3.3 feet: 110 cm/3.6 feet.

Current Rare Mythical Sightings: When discovered in 1880, the Swellshark was first described as Scyllium ventriosum, but was later changed to Cephaloscyllium ventriosum. The genus name comes from the Greek word kephale, which means “head”, and skylla, which means a certain kind of shark. The species name comes from the latin word ventrĭōsus, which means “large-bellied”.

Teeth and Jaw: The mouth is large and extends well behind the eyes. The teeth typically have three smooth cusps, but can have as many as five cusps. The middle cusp is the longest, and it is straight and pointed. Every swell shark has around 55–60 small teeth.

Head: They have flat, broad heads. The snout is blunt, with large, oval-shaped, cat-like, gold eyes that have nictitating membranes (lower eyelids). There are ridges over the eyes.

Denticles: The hatchlings develop paired rows of enlarged, rearward-pointing dermal denticles along the back, which act like a rachet, preventing the pup from slipping back into the egg case as it squirms out. These specialized denticles disappear from the young soon after hatching.

Tail: The caudal fin is asymmetrical and notched.

Demographic, Distribution, Habitat, Environment and Range: The Swellshark can be found in the eastern Pacific Ocean in California to Mexico and central Chile (40°N – 37°S, 126°W – 71°W). They can be found on the rocky bottom, in kelp beds or in other algae between depths of 16-1,499 feet, but typically stay around 121 feet. They are subtropical demersal.

Diet: They eat fish and crustaceans. They will eat prey that is dead or alive. Swellsharks will also look for food in lobster traps; they never miss an easy meal.

Predators of the swell shark include larger sharks and marine mammals including seals. Marine snails often bore holes in the tough protective coating of egg cases, consuming the developing embryo.

Ram-Suction Index: They feed either by sucking prey into their mouth or by waiting motionless on the sea floor with their mouth open, waiting to encounter prey. Swellsharks are ambush predators.

Aesthetic Identification: The Swellshark is a large, stout shark, that is strongly variegated. It has close-set dark brown saddles and blotches, numerous dark spots and occasional light spots on a lighter yellow-brown background. The ventral side is also heavily spotted. Usually the younger sharks are lighter in color than the adults. The gills of a swell shark are usually very small and tight. The second dorsal fin is much smaller than the first dorsal fin. The claspers are stout and short.

Biology and Reproduction: Swellsharks are oviparous. The eggs are laid in large, unridged, greenish-amber, purse-shaped egg-cases. When first laid, they are rubbery and pale, but soon harden and darken in color. There are long tendrils that allows an egg case to become attached to kelp, the reef, or the bottom. Some suggest that the length of the tendrils depends on the amount of surf action the region is under. The egg case which contains the embryo is approximately 2.5 cm–5.1 cm/2.0 inches by 7.6 cm/3.0 inches–13 cm/5.1 inches. The embryos will feed solely on yolk before they hatch. They hatch in between 7.5-10 months, depending on the temperature of the water. Pups have a double row of enlarged dermal denticles to help them exit the egg case. They emerge as miniature versions of adults, and are fully self-sufficient.

Swellsharks are florescent. Biofluorescence was reported publicly in Swellsharks in 2014 by Dr. Gruber. Researchers presented species-specific emission patterns, indicating that biofluorescence potentially functions in intraspecific communication and assists camouflage. Read about it here in the PSD Glow in the Dark Sharks.

Behavioral Traits, Sensing and Intelligence: Swellsharks are relatively sluggish and are mainly nocturnal. They lie motionless in rocky caves and cervices by day, often in small groups, and swims slowly at night, which suggests they are social in nature. Their coloration allows them to become perfectly camouflaged within their environments.

Like other members of its genus, Swellsharks can inflate their stomach with water or air (at the surface) to deter predators, they can also wedge themselves into crevices when inflated. When the shark feels threatened, it will bend its body into a U–shape, grab its tail fin with its mouth, and suck in water. When letting air out, the swell shark makes a dog-like bark.

Speed: They swim slowly and sluggish.

Swellshark Future and Conservation: They are of least concern. They are occasionally caught as bycatch in lobster and crab traps, gillnets, and trawls. Swellsharks are not typically consumed by humans due to the poor quality of meat.

Swellsharks are common in public aquariums, in part due to their longevity in captivity. Females have laid eggs in captivity.

Swellshark Recorded Attacks on Humans: Not a threat to humans.