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Species Profile: Upside-down Jellyfish (Cassiopea sp.) in the Home Aquarium

Eileen here.

One of the most iconic images of a jellyfish, the one most people think of, is that of a dome-shaped animal with long flowing tentacles drifting through the water. For the aquarium community however, this is not the one that we usually see in our tanks. A far more common aquarium jellyfish is the Upside-down Jellyfish.

There are about five different species of Upside-down Jellyfish, found mostly in the Caribbean and tropical western Atlantic Ocean. One of these species in particular, Cassiopea andromeda, has made its way to the Hawaiian Islands and seems to have established itself as a nuisance in waters around the state. It is another species, Cassiopea frondosa, that is usually found in the aquarium trade.

All jellyfish are planktonic by nature, meaning they move with the flow of the water instead of swimming against it. The Upside-down Jellyfish does not actually live in the water column like most other jellyfish. Instead, they use their bell much like an anemone uses its foot to attach to the bottom of a shallow environment like a lagoon, mangrove swamp or sand flat. While this attachment isn’t nearly as strong as an anemone, it helps the jellyfish to remain relatively stationary with its tentacles pointed up towards the surface.  The bell will often pulsate slightly to create a weak water flow over its tentacles which the jellyfish uses to filter-feed small food particles from the water. Upside-down jellyfish also have stinging cells known as nematocysts on its tentacles which it can use to stun larger prey. This feeding helps supplement its diet, but most of the jellyfish’s nutrition comes from the symbiotic algae in its tissue. The sunlight filtering through the water feeds the algae, which in turn produces food for the jellyfish while the jellyfish provides protection for the algae by keeping it alive in its tissue.

Upside-down Jellyfish are one of the easiest types of jellyfish to keep in home aquariums but still require special care and attention. As these animals can reach a diameter of almost a foot across, they should have plenty of flat, open sandy area to spread out. They also need very bright light to feed the algae in its tissue as well as periodic target feeding with foods like brine shrimp, baby brine shrimp, cyclops, zooplankton, phytoplankton and dissolved organic foods. The flow in the tank should be moderately low and any filter intakes should have some sort of covering to make sure the jellyfish doesn’t get sucked up by the current. The stinging cells on their tentacles can also harm other tankmates; do not keep with any shrimp, gobies or other invertebrate or small fish that can become food! These nematocysts can also sting aquarists so take care not to come into contact with the tentacles.

The flower-like appearance, unusual behavior and relatively easy care are making this jellyfish gain in popularity among home aquarists. With some extra TLC and research, Upside-down Jellyfish can truly be a unique addition to a home aquarium!