carlson at soest.hawaii.edu
Sat Nov 9 00:54:51 EST 1996
Observations re: bacterial infections of captive corals
Aquarists around the country who maintain corals in home aquariums have
observed a syndrome dubbed Rapid Tissue Necrosis (RTN) where corals
rapidly degenerate. Small polyp corals such as Acropora spp. seem
to be most susceptible. Usually this begins at the base of the coral as a
white area and rapidly spreads over the entire coral within 24 hours or
so. The tissue in the white areas peels off or otherwise degenerates, ie,
it is not a simple bleaching event. Under the microscope the usual
protozoa (cf. Helicostoma sp.) associated with other cases of RTN in large
polyp corals (e.g.Euphyllia spp.) are NOT observed.
Craig Bingman in New York has tested an antibiotic treatment which worked
in his aquarium. I wish to report that we have had similar success. This
may be of interest to those studying corals diseases in the field. IN our
case, one of our exhibit aquariums was accidentally overdosed with an
iodine solution. This (or something else) we surmise stressed the
acroporid corals in the exhibit. All of the acroporids in this exhibit
were cloned and the parent colonies in separate aquarium systems remained
healthy. Acropora microphthalma and A. austera both deteriorated rapidly
and were lost.
The remaining acroporids were treated when signs of the RTN appeared.
These species included A. cytheria, A. grandis, A. palifera, A.
gemmifera,and A. sp. Following Bingman's recommendation, these corals
were isolated in a 16 liter aquarium and treated with 5mg/liter
chloramphenicol. An airstone was added to the tank. After 24 hours the
treatment was repeated. Water from the "infected" tank was used to treat
the corals rather than "clean" water from our main source. After 48 hours
the corals were moved to our outdoor facilities. The RTN had "consumed"
up to 50% of some of these colonies before they were treated. The
treatment completely halted the progress of the "disease" and all of these
corals remain alive.
We did not conduct a test for bacteria but the lack of any other visible
pathogen and the fact that the progress of the RTN was halted by the use
of chloramphenical strongly suggests that bacteria were the primary
pathogen. The fact that we used "infected" water in the treatment tank
helps us rule out the possiblity that simply transferring the corals to a
different tank with different water elliminated the problem.
Additionally, Craig Bingman reports that he treated his entire aquarium
system with chloramphenicol with the similar results, ie, the RTN
I am reporting this partly to benefit those who are maintaining corals in
either aquariums or laboratory conditions. It may or may not have any
applicability to field situations. I am not familiar with the literature
on bacterial infections in corals but I assume that this in itself is
nothing new. Finally, just a warning to anyone using chloramphenicol --
it is considered very hazardous and should be used with extreme caution.
Other antibiotics may be safer and just as effective in treating corals.
For those who may be wondering: effluent from our coral systems flows
into the sanitary sewer system, not into the ocean.
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