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Contagious Rapid Tissue Degeneration In
Susceptible Aquarium Corals: An SDR-Like Condition Eric H. Borneman Microcosm, Ltd., 2222 North Fountain Valley, Missouri City,
TX, USA 77459. Shut-Down Reaction (SDR) is a coral
disease for which little is known because of the speed at which coral mortality
and tissue loss occurs. In aquaria, a
similar condition exists which has become known as Rapid Tissue Necrosis (RTN).
It is not yet known whether true necrosis is involved, but the very rapid
tissue degeneration that occurs is highly contagious and almost 100% lethal
without intervention. Pre-sloughing conditions include abnormal mucus density
and production (or cessation), a strong aromatic smell, retraction of polyps,
and a deepening or pinkish-brown color change in the tissue. Healthy and
established susceptible colonies placed in a closed system with a coral showing
signs of this condition will begin a sloughing reaction within hours. Bleaching
is not evident in affected colonies as tissue is sloughed from the corallum in
sheets and strands with zooxanthellae intact.
Banding patterns similar to White-Band Disease (WBD) may be present;
with tissue loss frequently occurring from basal tissues outwards toward branch
tips or margins. It can be induced by various acute and prolonged stress events
such as histoincompatibilities, physical competition, temperature,
sedimentation, rapid drops in redox, and injury. Corals with thin tissue and
small polyps are most frequently affected, with acroporids and pocilloporids
being the most susceptible. Many genera are unaffected or seemingly immune to
this condition. Prompt isolation of a colony showing signs of sloughing will
often halt the progression of tissue loss.
The ability to monitor and control parameters in closed aquaria and the
nature of this condition can potentially provide insight into the physiology of
the coral disease response.
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