Tokyo Sea Life Park began exhibiting the Japanese sea bass (Lyophyllum decastes) in its "Tokyo Sea" area in July 2012. This was the first time the aquarium had raised the jellyfish from the polyp stage to full-grown jellyfish.

Many jellyfish have two phases: one in which they drift in the ocean, and another in which they sess themselves. During the sessile phase, they resemble sea anemones and are called polyps. From these polyps, ephyra, which are the jellyfish larvae, detach and grow into the familiar "jellyfish" we know today.

The red jellyfish on display are individuals that we carefully raised over time from polyps that we received from Marinepia Nihonkai, Niigata City Aquarium, in February 2012. Since red jellyfish are sensitive to high temperatures, we kept the water temperature below 14℃. We fed them brine shrimp, a type of zooplankton, and as they grew, we mixed in live mysid shrimp. We also paid attention to the strength of the water flow so that the jellyfish would not sink to the bottom of the tank or bump into the walls, but instead move slowly around the tank. We were relieved when their appearance and body color finally started to resemble those of a red jellyfish.

The red jellyfish can be seen all over Japan from early spring to autumn. With its orange radial pattern on its bell and long tentacles, it is a very beautiful creature, but it is actually a dangerous jellyfish. As many people may know, most jellyfish have stinging cells called nematocysts, and when they come into contact with something, the nematocysts pierce it and inject venom. The nematocysts of the red jellyfish are strong, and being stung is said to be quite painful. You can also be stung by a dead jellyfish that has washed ashore, so caution is necessary.
With the weather getting so hot that you start sweating just by stepping outside, many people will be heading to the beach. The sea offers plenty to do, from swimming and fishing to exploring the tide pools, but don't forget that there are also dangerous creatures that you need to be careful of.

[Namiko Tomura, Animal Care and Exhibition Staff, Tokyo Sea Life Park]

(August 3, 2012)