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World's largest captive jellyfish on display

A jellyfish captured by a fisherman off the coast of East Yorkshire is believed to be the largest in captivity after being donated to The Deep aquarium in Hull.

The Lion’s Mane jellyfish (Cyanea capillata) in question has a bell diameter of 14 inches (35.5 cm) but, as the largest species of jellyfish in the world, can reach sizes of 7 feet in diameter with tentacles longer than 120 feet.

The Deep’s jellyfish aquarist Tom Rowe explained, “We were delighted to receive this wonderful animal.

"It’s the first time I’ve seen a Lion’s Mane jellyfish in the region and it is by far the largest jelly ever displayed at The Deep. As far as we know it’s the largest jellyfish in the world in captivity.”

Jellyfish display tank

Following a short period in quarantine, the jellyfish, which has a slight tear on the edge of its bell but is otherwise in very good condition, was moved into a 3500-litre cylindrical display tank.

Tom Rowe explained, “Keeping any species of jellyfish can be extremely difficult; tank shape, flow, diet and water parameters need to be spot on or the animal can quickly perish.”

Rowe added, “They can be kept with other Lion’s Manes but are best kept alone when this size as they can be cannibalistic if one starts to weaken. Ours appears to be doing incredibly well and instantly fed on three large moon jellies.”

Temperate species

The Lion’s Mane jellyfish is a temperate species with a huge geographical range that includes the waters of the Arctic, Northern Atlantic and Northern Pacific. The captive specimen is being kept at 13°C to match the sea temperature from where it was caught.

The natural diet of the Lion’s Mane jellyfish consists of zooplankton, small fish, ctenophores (comb jellies) and other jellyfish.

Although they will accept a wide range of foods, they do require some form of gelatinous animal in order to maintain their condition and aid growth.

Jellyfish culture

The Deep, which heads the BIAZA (British and Irish Association of Zoos and Aquaria) jellyfish research group, has been culturing a number of jellyfish species over the last 6 years, including the Moon jellyfish Aurelia aurita and the Upside-down jellyfish Cassiopeia xamachana.

Rowe added, “The next step is to begin culturing the Lion’s Mane and another native UK species, the Blue Lion’s Mane Cyanea lamarckii."