Aqua World Ibaraki Prefecture Oarai Aquarium, which keeps more shark species than any other aquarium in Japan (55 species as of December 2025), has started displaying Australian swellshark eggs for the very first time, as of May 14, 2026 (Thursday).
About the Australian Swellshark
The Australian swellshark (scientific name: Cephaloschyllium laticeps; order Carcharhiniformes, family Scyliorhinidae) is found in shallow coastal waters and at depths of up to 60 meters throughout the southwestern Pacific Ocean and along the southern coast of Australia. It can grow to a maximum length of approximately 150 cm.
The species is closely related to the Japanese nanukasame (banded houndshark). Like other members of its family, the Australian swellshark has a distinctive defensive behavior: when threatened, it gulps seawater to inflate its body. The English name "swell" refers directly to this swelling ability.
Distinctive Egg Cases with Wavy Patterns
Eggs from the nanukasame family of sharks are popularly nicknamed "mermaid's purse" because of their shape and size. While nanukasame eggs have smooth shells, the Australian swellshark's egg cases are covered in beautiful curved ridges that form undulating, wave-like patterns across the surface. The significance of these patterns has not yet been determined.
The eggs currently on display are developing steadily, and it is possible to see a baby shark growing inside the case.
A New Experience for Keepers and Visitors Alike
The aquarium obtained the eggs in early May 2026. Since Australian swellsharks have never been kept at the facility before, much remains unknown about the species. For the shark keepers, this is a first experience not only raising the eggs but also seeing the hatchlings emerge. Visitors are invited to observe the eggs and imagine what the baby shark inside might look like.
The "Samekko Room" on the 5th Floor
The eggs are on display in the "Samekko Room," located in the Nagomi no Umi (Calming Sea) Zone on the 5th floor. This area showcases the aquarium's ongoing shark breeding and reproduction research, including baby sharks born at the facility.
Display started: May 14, 2026 (Thursday)
Location: 5th floor, Nagomi no Umi Zone — Samekko Room
Note: Only the eggs are on display. Adult Australian swellsharks are not exhibited. Display content may change depending on the condition of the animals.
