I know almost nothing about these creatures, but let me see if I understand
what you're saying.
Your comments about constant current and no obstructions suggest that the
jellies have no propulsion systems of their own, and are completely at the
mercy of the current. If that is so, then would corners in the tank create
dead zones where they would become hopelessly stuck? Do they require
constant motion just to live? What about in the polyp stage?
Steven A. Ellis
Kennesaw, GA
At 09:01 AM 10/2/02 -0700, you wrote:
>Casper, the freshwater jelly (Craspedacusta sowerbyi) are really neat
>critters. There isn't a bunch of stuff known about them because unlike most
>jellies, they spend most of their life in the hydra stage and only a few
>weeks (as others have indicated) in the medusa (or "jellyfish") stage. They
>are relatively difficult to keep in captivity and the way that most public
>aquariums keep jellies is in a bare tank that has rounded corners. There
>are two "standard" ways to design a jelly tank: either a Kriesel tank or a
>cylinder tank. This is not to say that they can not be kept in other
>systems, it is just that since jellies are planktonic, no obstructions is
>the best way of keeping them. In both systems, the object is to keep the
>animal moving in the current and most importantly to keep it away from and
>intakes into the filter (a jet of water blows past the intake screen to keep
>the jelly from being sucked onto the screen). A Kriesel tank is basically a
>cylinder tank (or an oval shaped tank) that is on its side. It is usually
>less than 18 inches from front to back. Also, for other jellies
>especially, air lifts are a big no no. Air usually gets trapped under the
>bell and can pose serious problems. I do believe that the fw jelly is the
>only species found in freshwater, and finding the polyp stage is virtually
>impossible. Medusa's usually bloom late in the summer and not every
>year-there can be long periods of time when there are no medusa's around.
>There have been aquariums that have worked with fw jellies but because they
>are so short lived in the "jellyfish" stage, it is very difficult to keep an
>exhibit going year round. Check out
>http://microscopy-uk.org.uk/mag/artnov99/fwjelly.html for more information.
>
>Nick Zarlinga
>Aquarium Biologist
>Cleveland Metroparks Zoo
>216.661.6500 ext 4485
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