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

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!


  1. avatar

    I am keeping 6 Cassiopea (~3 inch diameter) in a 12 gallon Nanocube tank at the moment. They are relatively easy to care for and readily feed on brine shrimp. However, a common problem that I have encountered is the clouding up of the water. Despite both mechanical filters and carbon/phosphate bags, the water clouds up quite badly at least once a week. Water clarifiers do little good, and increasing water flow also does not aid the clarification. My assumption is that the jellies are secreting mucous that is highly bacteriophilic and promotes bacteria growth. The animals do leave behind a small mucoid secretion on the glass walls prior to moving to a new location. Settling on the fine sediment also reveals a mucoid substance. Perhaps water chemistry is inadvertently promoting mucus secretion?

  2. avatar

    Hello Rick,
    I have not found any references that the mucus from the jellyfish directly promotes bacterial growth, but since it is an organic substance and can contain zooxanthallae as well as various proteins, bacteria will certainly feed on it and can cause a bloom. How long has this aquarium been established? Have you done any significant water changes (over about 25-30%) prior to the water becoming cloudy? How often are you feeding the jellyfish? My initial reaction would be that the tank is experiencing bacterial blooms similiar to that experienced during a “new” tank’s cycling process(http://blogs.thatpetplace.com/thatfishblog/2009/02/11/new-tank-syndrome-in-home-aquariums/ and http://blogs.thatpetplace.com/thatfishblog/2009/01/12/clearing-cloudy-water-common-aquarium-questions/ ).

    Small tanks are especially vulnerable to chemistry fluctuations and it is entirely possible that this is happening in your aquarium, causing both mucus production as a stress response in the jellyfish and bacteria blooms in the water itself. I would encourage you to monitor and record the temperature, pH, Ammonia, Nitrite, Nitrate and any tank maintenance to see if you can see any patterns that might be triggering the blooms.

  3. avatar

    I just bought a tank specifically designed for jellyfish and picked up 3 of the upside down jellyfish. What is the ideal temperature and how saline should the water be?


  4. avatar

    temp should be 75 to 82, Specific Gravity Range 1.022-1.026…the tank should really be cycled before introducing jellies

  5. avatar

    Everywhere I look it says these jellies are found in mangrove swamps. I have even seen these jellies wild in mangrove swamps in Bermuda. But also everywhere seems to be saying they need a minimum of 30 ppt. I thought mangrove critters were a bit more euryhaline? I really want to do a mangrove set up with these guys, but some of the other tank mates I’m hoping for are more brackish. Would these jellies manage at 25 ppt? If not how do they cope in the wild with mangrove swamps changing salinities often?

  6. avatar

    Hi Ben, You are correct that these jellyfish are found in a lot of mangrove swamps, turtle grass beds and similar environments and the salinity in those environments as a whole can vary. The average salinity in most of these swamps is 32-35ppt but it can vary depends on where in the swamp the measurement is taken and the topography and geography of the swamp itself, and an individual point of the swamp may be more stable or fluctuate more than another point. Jellyfish would generally be found towards the more fully saltwater “ocean end” rather than closer to the freshwater “end”. If you acclimate them very slower from a full salinity to 25ppt, they may tolerate it but I wouldn’t recommend keeping them below around 28-30ppt. You may want to look for a supplier or collector that is already keeping or collecting them at a lower salinity so it is less of a change for them. For example, our supplier collects from a fully-saltwater environment and we keep our systems at around 1.025 Specific Gravity (about 34ppt).

About Eileen Daub

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Marine Biologist/Aquatic Husbandry Manager I was one of those kids who said "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and in other local roles. If that isn't bad enough, I'm a proud Crazy Hockey Fan (go Flyers and go Hershey Bears!).