Did you know that there are sharks able to inflate their belly to about double or triple its regular size like pufferfish do? One of them is the aptly named swellshark (Cephaloscyllium ventriosum).

Cephaloscyllium ventriosum 3.jpg
Cephaloscyllium ventriosum“ von Rennett Stowe from USA – shark and fish. Lizenziert unter CC BY 2.0 über Wikimedia Commons

Swellsharks live in kelp forests on the subtropical eastern coast of the Pacific Ocean. They are nocturnal and lie in daytime in congregations at the bottom, sometimes piled up on one another. When threatened, the swellshark dives headfirst into any available rocky crevice, bends its body into a U-shape to stash its tail away, too (secured by grasping its caudal fin in its mouth) and inflates by swallowing water and holding it in the forward potion of its stomach (locked in by a sphincter). Such wedged it, the shark is difficult to bite or otherwise forcibly evict.

At night, swellsharks can detect prey that they can neither see nor smell, using electroreception. They are slow, sluggish swimmers and ambush fast-swimming prey or use their relatively large mouth – proportionally wider than that of the White Shark – by swimming through a shoal with it gaping wide open. Swellsharks use a internal mechanism (circadian clock) to maintain a strickt 12 hour rhythm (with the same little rhythm shifts in constant darkness like humans).

Like almost all catsharks, they lay egg cases, using curly tendrils at each end to anchor them. Their length varies between less than 2 centimetres -1 inch- and 200 centimetres -79 inches- depending on the current. In order to more efficiently extract oxygen from the relatively stagnant environment within the egg case, the pre-hatch swellshark has got different hemoglobin than the adult one.

Swellsharks are biofluorescent.