J. Fish Biol. 73, 17–34 (2008)

Credit: T. YAMANAKA/AFP/GETTY

An examination of a one-tonne megamouth shark (Megachasma pelagios; pictured) caught off the coast of Japan indicates that the species has a feeding method previously seen in whales, but never before in sharks.

Fellow plankton-feeding sharks — the whale shark and the basking shark — typically feed by swimming through clouds of their quarry with their mouths continuously open. But the highly elastic skin and loose connective tissue around the jaws of the megamouth point to it relying on an 'engulfment' technique like that used by humpback whales, say Kazuhiro Nakaya and his colleagues at Hokkaido University in Japan.

This would involve the fish swimming towards a shoal of plankton with its mouth slightly open, sucking, and then gradually expanding the mouth and throat cavity to fit more and more in. When its mouth is full, the shark 'gulps' — sieving and swallowing prey while expelling seawater through its gills.