Captive Raised Moon
By Jim Stime, Jr.
Jellyfish are the newest item available in the marine aquarium hobby.
Those amazing looking large public aquarium tanks that display
beautifully sculpted jellyfish creatures that float so gracefully are
now being manufactured in self-contained free standing systems, called
the Jelliquarium, specifically designed for use within homes and
Public aquarium jellyfish tanks are called a kreisel. It is supposedly
a German word that means spin or carosel. The basic design of a
jellyfish tank is to create a means where water enters and exits the
tank, as well as, suspends its inhabitants weightlessly within the
center, all without damaging the soft gelatinous bodies of the
Water is introduced into the tank in the form of a sheet or layer of
water, called a laminar layer, which moves along the inside
circumference of a round or oval tank. This layer acts as a boundary
and it is the mechanism that keeps the inhabitants suspended within
the tank. In general, the incoming water is diffused across a large
screened exit. This current of water gently pushes the jellies away
from the exit screen, and that exit screen is so exaggerated in its
size that its ‘draw’ is so diffused, or weak, that the jellyfish
typically are not pulled into it.
Jellyfish are from a branch in the animal kingdom called Cnidaria. All
Cnidarians share a similar body plan, which can be described as a sack
within a sack. These organisms posses no distinct head or structural
organs, and yet they all possess one thing in common, Cnidae,
specially modified stinging cells or nematocysts.
There are four basic groups of Cnidarians;
which contain the familiar anemones and corals, Hydrozoans, such as
Fire coral, and the
which contain the extremely dangerously Box Jellyfish.
being the forth group of Cnidarians contain the more familiar
jellyfish. The 200 plus species of scyphozoans range from a simple 1
centimeter clear disc to a huge multicolored organism with long and
numerous dangerous stinging tentacles.
The Moon jellyfish,
aurita species, are the most documented and easiest to raise of the
jellyfishes. They are commonly seen in shallow harbors or boat marinas
and are recognized as a pale white pulsing disk with a recognizable
four leaf clover design within their round bell. The bell is edged
with a fringe of fine tentacles that help transfer food items to the
four trailing oral arms. Moon jellyfish generally do not have a strong
Jellyfish are sexually active at an early age. As with many aquatic
forms of life the male releases sperm into the water column which
fertilize the eggs that the female has attached to her oral arms. Once
the fertilized larvae have detached from the female they will settle
out onto the bottom and develop into a stationary polyp.
A Moon jellyfish polyp looks a like tiny white anemone which attaches
itself to almost anything. Most polyps seem to settle out in areas
where the water flow is slow enough to allow the larvae simply to drop
down onto the bottom of the container.
As with most Cnidarians a jellyfish polyp is composed of a
central column that has a foot for attachment and an oral disc for the
intake of food and exit for waste products. The oral disc has a number
of tentacles surrounding it, which provide protection through stinging
and capture of food items. It is this oral disc that produces or
segments and separates from the polyp in what is commonly called
asexual division, budding, or also referred to as strobilation.
As a result of strobilation the oral disc portion of the polyp
detaches from the main body of the polyp and pulses away. This pulsing
disc, which resembles a small snowflake, is now a free swimming
juvenile jellyfish called an Ephyra.
Ephyra begin pulsing before they detach from the polyp. It is
this pulsing that is the main method of separation from the polyp. The
pulsing is not just a means of propulsion but is also how the
jellyfish moves its food items to its mouth. Moon jellies do not
pursue food items, more so they simply bump into it. As the bell
portion of the jellyfish comes in contact with food particles they
become held onto by a slime coating. The pulsing action of the bell
moves the food items to the outer rim of the bell where the fringe
tentacles grasp and maneuver the food through a whipping action around
the edge of the bell where the longer oral arms grasp it. These oral
arms pull the food items up into the mouth of the jellyfish.
Up to this point a simple square cornered tank or glass jar
with a slow flow through could hold your polyps, but from this point
onwards these small jellies need a flow of water that keeps them
moving and suspended. This is achieved through the use of slight
aeration or a tank designed for this need. Ephyra need to be kept in
suspension at all times. If allowed to settle they will quickly become
consumed by other polyps or perish as a result of starvation.
Within the next two weeks the Ephyra go through a slight
metamorphosis. First is the development of the four oral arms. These
oral arms are what will pull the food up into the jellyfishes body
cavity. Next to change are the eight radial arms, which gave it the
snowflake look, that begin to fill in between each arm with a solid
tissue and develop into the more commonly seen bell shape.
From day one both the polyps and ephyra are fed freshly
hatched, enriched in some manner, baby brine shrimp. Feedings are two,
three or four times a day depending on how fast you want them to grow.
Growth rates are anywhere between 60 and 120 days to become a 2 inch
diameter Moon jellyfish.
As the jellyfish grows in size they can be fed food items that
are larger in size. There are a number of planktonic foods available.
All are eagerly drawn up by the jellies and noticeably fill their
digestive guts with the food items. I suspect that it is the
nutritional value of the food items, along with variety, that will
sustain or improve the quality of life of these juvenile jellies.
Maintenance consists of wiping algae growth and siphoning out
waste and uneaten food debris. Algae growth is based on the amount of
light and the length of time that the light source is on. Wiping algae
from the interior is like any other aquarium. One uses a hand pad or
pad-on-the-end of some long handle. Free floating and heavier debris
will settle at the bottom of the tank and will need to be siphoned
out. This becomes a surgical process as one can easily suck up
jellyfish if they get too close to a siphon wand. Polyps that have
settled within the debris will sting the young juveniles and possibly
Moon jellyfish do not acclimate very quickly to different
salinities so the amount of water used in a water change, or the
result of siphoning out debris, is relatively minimal. The replacement
water should be of the same salinity, pH and temperature, the later
being a bit more difficult, and only enough to replace the siphoned
out water. Taking into consideration that jellyfish are 95% plus water
they will react negatively if their aquatic environment is radically
altered. Moon jellyfish that are attempting to adjust to big changes
will respond by bloating and decreasing the amount of pulsing.
It is not a good idea to mix species, and never collect or
capture jellyfish with a net. Always use a container that the entire
animal can fit into and simply scoop the jellyfish from its tank or
shipping container, supported by a container full of water. I have
found that by placing a finger size hole in the bottom of a plastic
container allows me to drain some of the water from the transfer
container. This finger hole allows me to move the container through
the water easier when it is submersed.
When raising Moon jellyfish they need to be fed a minimum of
twice daily. At first this seems like a daunting task but once you get
into the routine it is not that time consuming. Freshly hatched brine
shrimp can be easily raised if you have the right equipment.
Decapsulation and enrichment are additional chores that you may decide
to get involved with. Once the jellies reach 2 inches other larger
food choices, such as frozen Cyclopeeze, should be fed. These thawed
or liquefied foods are dispensed easily with a turkey baster directly
into the tank.
Lighting is dependent on the species being kept. Some
jellyfish, like corals, are photosynthetic. Moon jellyfish are non
photosynthetic and do not require light. A brightly illuminated tank
shows off its inhabitants well but also requires more effort with
entire process is fairly easy, once it’s understood, and the amount of
daily time is minimal once a routine and proper equipment are used.
The end result is a spectacular display of some of the most graceful
creatures the aquarium hobby now has to offer you, in your home or
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