RE: NANFA-- JellyFish

Nick Zarlinga (njz_at_clevelandmetroparks.com)
Wed, 2 Oct 2002 10:51:24 -0700

Jellies obviously do pulse on their own and can create their own direction
of movement. The problem is is that they often get stuck on objects or in
the intake of a filter. They are certainly not powerful swimmers and that
is what the purpose of the current is and no corners. The fw jellies, being
that they are so small, should be much more forgiving. The larger jellies
such as the moon jellies and the ones with the longer stinging tentacles
like the nettles pose the most problems, that is why there are special
engineering requirements on the tank. Also, with no objects in the tank,
you can manipulate the presentation of the display with funky lighting to
enhance the effect. It may not seem natural to display them in a bare tank,
however remember that they are pelagic and swim in the water column, so
there is no real need for any aquascaping to hide in, breed on, etc. In the
polyp stage, jellies look like little hydras and then strobilate, that is
they bud off tiny "buttons" called ephyra which grow into the medusa stage
that we are familiar with. Next time you make it to a public aquarium, look
along the edges of the jelly tank and there will be thousands of little
polyps that look like fuzzy hydras. That is the sessile stage of the life
cycle. Again, fw jellies do the same thing, it is just that the polyp stage
is probably very, very small and virtually impossible to see while
snorkling. Add also that they are probably virtually transparent. They are
cool but I think that it would be incredibly difficult to have enough
cultures going at various stages to ensure enough medusae present year
round. I would imagine that temps, water chemistry, and lighting would all
have to be manipulated to enduce strobilation. When the medusa are present,
then you would have to put them into you exhibit tank. The next batch of
jellies would then be strobitating within a couple of weeks to replace the
medusae that will shortly be dying in the exhibit; so on and so on. Even
the big public aquariums don't think that it is worth the effort to keep a
constant, year round display.

Nick Zarlinga
Aquarium Biologist
Cleveland Metroparks Zoo
216.661.6500 ext 4485

-----Original Message-----
From: owner-nanfa_at_aquaria.net On Behalf
Of Rose Lawn Museum
Sent: Wednesday, October 02, 2002 7:15 AM
To: nanfa_at_aquaria.net
Subject: RE: NANFA-- JellyFish

Thanks, Nick

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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