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Aquarium.Net Treatments for Invert Pathogens

Sept. 1996 Pathoggens and treatments for invertebretes in a reef aquarium, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Treatments for Invert Pathogens

By Dana Riddle

Study of invertebrate pathogens is still in its infancy with most research having been conducted on intensely cultured animals such as shellfish.

With recent advances in captive culture of Tridacna calms, soft corals and stony corals, the need exists for medicines to combat invertebrate pathogens.

This short paper will review our current knowledge.

Invertebrates are susceptible to a variety of ailments. Infective agents include viruses, rickettsiae, chlamydiae, mycoplasmas, bacteria, fungi, algal cells and protozoa (Peters, 1988) . Diseases affect the life span, life cycle, abundance, reproduction, metabolic performance and tolerance to natural and man-made stress (Kinne, 1980) .

Currently, treatment of coral and Tridacna diseases is limited to freshwater dips (which is effective against platyhelminthes (flatworms) and some bacterial or protozoal infections.) Soft corals such as Sinularia (Dead Man's Hand), Sarcophyton (Leather corals) and some of the sturdier stony corals (e.g. Catalaphyllia - Elegance corals) can withstand this treatment with little or no lasting harm. Small-polyped stony (SPS) corals such as Acropora (Staghorn corals), Porites and others may be killed or made ill by this treatment (Antonius, 1988) .

Bacteria

Bacteria are single celled organisms about 1 µm in diameter. Most possess a rigid cell wall. All lack a true nucleus and are thus considered prokaryotic. Bacteria may be classified in many ways; a negative or positive reaction to a Gram stain is but one. Gram-negative bacteria lose a stain or are decolorized by alcohol and generally possess a cell wall more complex than gram-positive bacteria (which, conversely, retain Gram's stain or resist decoloring by alcohol and have cell walls composed of peptidoglycan and teichoic acid).

Marine sediments are predominated by two bacteria - Vibrio and Pseudomonas (DiSalvo, 1973) ; the remainder (about 30%) are numerous other genuses, including Moraxella, Nitrobacter, Nitrosomonas, etc.

Vibrio - Genus of gram-negative bacteria (Family Spirillaceae). Vibrio parahaemolyticus and V. vulnificus inhabit many marine organisms. V. alginolyticus and V. anguillarum can cause mass mortalities in clams (Delbeek and Sprung, 1994) . Unidentified Vibrio species are thought to be a natural control for Acanthaster - the Crown-of-Thorns starfish (Sutton et al, 1988) . V. tubiashii is a known pathogen of invertebrates.

Pseudomonas - A genus of gram-negative, strictly anaerobic bacteria. Some species are pathogenic to vertebrates, plants and invertebrates. Sutton et al (1988) describes Pseudomonas as a pathogen of the Crown-of-Thorns starfish.

Moraxella - A genus of bacteria found as parasites and pathogens in warm blooded animals. It has been noted as a starfish pathogen as well.

Mycoplasma - A genus of pleomorphic (various shapes found in a single species), gram-negative, aerobic to facultative anaerobic microorganisms.

Chlamydiales - An order of coccoid (spherical), gram-negative bacteria that multiply within the cytoplasm (cellular fluids exclusive of the nucleus).

Rickettsiae - An order of gram-negative bacteria occurring as short rods, chained cocci, and pleomorphic forms. They are non-motile. Pathogenic rickettsiae include the organisms which cause Typhus and Rocky Mountain Spotted Fever.

CORAL DISEASES

Arnfried Antonius has authored numerous papers on coral pathogens. He notes that many bacteria normally live on or within corals. Various environmental factors such as temperature, salinity, pollution (or more correctly eutrophication), exposure to toxic metabolites and others can induce stress and subsequently make the coral susceptible to diseases from these naturally-occurring micro-organisms. He lists the coral diseases as:

BLACK BAND DISEASE (BBD)

The blue-green cyanobacteria Phormidicum corallyticum (Antonius, 1981) and Oscillatoria (Littler et al, 1989) are the apparent causes. These bacteria cause coral tissue necrosis by exuding a toxic metabolite. The dead coral skeleton left behind is in stark contrast to the "black band" of cyanobacteria. BBD correlates with excessive water column nutrient levels and temperature. BBD has been found to disappear at temperatures below 26 degrees C (78.8 degrees F). This disease is known to occur strictly in shallow-water.

Antonius (1988) found many corals not susceptible to BBD in nature to be readily infected in aquaria. A short listing of corals found in the Atlanta area pet shops and their susceptibility to BBD is listed below.

I = Immune R = Resistant S= Susceptible Slow (tissue loss 1mm per day) M = Susceptible Medium (tissue loss 1 to 3 mm per day) F= Susceptible Fast (tissue loss 3 to 5 mm per day)

  • Stylophora - S
  • Pocillopora - M
  • Acropora - F (12 species)
  • Montipora - not tested, but I have a M. digitata that has been infected by a red cyanobacteria and has lost tissue at a very slow rate.
  • Pavona - S
  • Cycloseris - I
  • Fungia - I (5 species)
  • Herpolitha - I
  • Porites - R (5 species)
  • Favia stelligera - M
  • Favia - R (2 species)
  • Favites chinensis - S
  • Favites - R (4 species)
  • Goniastrea retiformis - F
  • Goniastrea pectinata - M
  • Platygyra daedalea - R
  • Platygyra lamellina - M
  • Hydnophora microconos - M
  • Hydnophora exesa - S
  • Galaxea - R
  • Tubipora - coral tissue initially destroyed, then the coral rejected the disease; that is, it attacked and overcame the infection. Only occurrence in over 50 species tested.

WHITE BAND DISEASE (WBD) :

Black band Disease is easy to identify; White Band Disease is not. With SPS corals, it is difficult to distinguish between "bleaching" and WBD. Researchers well acquainted with the disease had to scrape tissue from species of Acropora to determine if an infection existed. WBD advances and destroys tissue with no apparent cause. It occurs most often in upper reef areas. This disease seems to occur all year round with slightly more cases during warm weather. Antonius (1988) noted Acropora species to be infected in pristine waters. The stony coral Porites may also be infected. Antonius made a correlation of various environmental factors relating to an increase in WBD. They are: strong wave action, salinity swings due to rainfall or run-off, and, possibly, toxic metabolites from naturally occurring reef algae turfs.

Microscopic examinations of infected tissues are discussed by Peters et al (1983) and these tissues were found to contain "unusual" gram-negative, rod-shaped bacteria. Further, Dustan (1977) found healthy colonies could be infected by exposure to diseased tissues from other colonies, suggesting a viral, bacterial or fungal cause.

SHUT DOWN REACTION (SDR) : This disease is likely to be stress related as the coral very quickly fails to expand and turns to a decaying mass. SDR is apparently not related to temperature stress as Delbeek and Sprung (1994) suggest; however, lower temperatures may slow SDR which suggests a bacterial or fungal cause.

POSSIBLE TREATMENTS FOR CORAL DISEASES

Not much information is available on diagnosing, much less treating, coral diseases. However, this preliminary research suggests those chemicals effective against gram-negative bacteria should be investigated.

CHLORAMPHENICOL : Initially described by Wilkens (1990) as an antibiotic for soft coral "cuttings" and later broadened by Delbeek and Sprung (1994) to be a "cure-all" for stony coral ailments. Chloramphenicol, or chloromycetin, is a broad spectrum antibiotic which is effective against many gram-positive and -negative bacteria, rickettsiae, spirochetes and some viruses. It is only slightly soluble in water but freely soluble in ethyl alcohol. It is stable at high temperatures and is effective at a pH of 2 to 9. It inhibits protein synthesis when amino acids are transferred from the soluble RNA complexes to the ribosomes.

This drug is not (or should not be) available to hobbyist. Since two widely accepted works on reef aquaria specifically recommend this drug, it would seem that there would be a demand for an acceptable substitute.

ERYTHROMYCIN : A broad antibiotic produced by Streptomyces and used against gram-positive and a certain few gram-negative bacteria. A good candidate for treatment of BBD, but not WBD.

TETRACYCLINE : Produced by Streptomyces, the base and the hydrochloride salts are used as an antiamebic, antibacterial and antirickettsial agent. There are several "tetracyclines" - chlortetracycline, oxytetracycline (Terramycin) and tetracycline. Chlortetracycline (Aueromycine) is practically insoluble in water. It is very similar to chloramphenicol and acts as a bactericide in high concentrations and as a bacteriostatic in lower concentrations. It has a very limited shelf life in solution but is very stable in crystalline form.

STREPTOMYCIN : Obtained from Streptomyces griseu, this drug inhibits many organisms resistant to penicillin and sulfonamides. It is effective against many gram-negative bacteria. Streptomycin is water-soluble and has an excellent shelf life.

PENICILLIN : A group of compounds produced by the fungi Penicillium, these drugs are used as bacteriocides and bacteriostatics against gram-positive pathogens, some gram-negative pathogens as well as some spirochetes and fungi. There are several types of Penicillin: F, Dihydro-F, G, K and V. Penicillin G was found to be effective against Vibrio and Pseudomonas infections in the Crown-of-Thorns starfish (Sutton et al, 1988) at a dosage of 100 units per ml. Crystalline sodium or potassium salts are freely soluble in water.

NEOMYCIN : A broad spectrum antibacterial agent produced by Streptomyces fradiae. It is effective against a wide variety of gram-negative bacteria.

RIFAMPIN : Suggested for use in treatment of coral ailments by Delbeek and Sprung (1994) , this drug is derived from Rifamycin SV.

CEPHALOTIN : This drug is effective against a wide variety of gram-positive and gram-negative bacteria. It is not effective against Pseudomonas.

QUATERNARY AMMONIUM COMPOUNDS : Delbeek and Sprung (1994) report the Tetra product "Marin-Oomed" to be effective against flatworm infestations of the soft coral Sarcophyton. This quaternary ammonium compound for is but one of several on the market for use in marine aquaria. These compounds are proven, effective antifungal and antiprotozoal agents as well. In addition, they are exceptionally effective against gram-positive bacteria. To a lesser degree, gram-negative bacteria are affected. In high concentrations, they are bactericide; lower concentrations are bacteriostatic.

RECOMMENDATIONS

First and foremost, the reef keeper should work to identify the source of stress (high or low temperature, polluted water, insufficient water movement) and take action to correct the situation. If treatment must take place, use the following guidelines:

*"Black Band Disease" treatment - Only rarely seen in aquaria (gorgonias seem to be suspectible), the hobbyist is encouraged to experiment with Erythromycin.

*"White Band Disease" treatment - Since the exact cause of this disease is unknown but possibly related to gram-negative bacteria, proceed with experiments with Neomycin or Streptomycin.

*Coral "cutting" disinfectant - Proceed with trials with Tetracycline.

*"Shut Down Reaction Treatment" - Proceed with trials with broad spectrum antibiotics.

References

Antonius, A., 1981. Coral reef pathology: a review. Proc. 4th Int. Coral Reef Symp., Manila, Vol.2, 1-8.

Antonius, A., 1988. Black band disease behavior on Red Sea reef corals. Proc. 6th Int. Coral Reef Symp., Australia, Vol. 3, 145-150.

Antonius, A., 1988. Distribution and dynamics of coral diseases in the eastern Red Sea.

Proc. 6th Int. Coral Reef Symp., Australia, Vol. 2, 293-298.

Delbeek, J. and J. Sprung, 1994. The Reef Aquarium, a comprehensive guide to the identification and care of tropical marine invertebrates. Ricordea Publishing, Coconut Grove, Florida.

DiSalvo, L., 1973. Microbial Ecology In: Biology and Geology of Coral Reefs.

Kinne, O. (ed), 1980. Diseases of Marine Animals, I., General Aspects, Protozoa to Gastropoda. John Wiley and Sons, New York.

Littler, D., Littler, M., Bucher, K. and J. Norris, 1989. Marine plants of the Caribbean. Airlife Publishing, Shrewsbury, England.

Pelczar, M. and Reid, R.,1972. Microbiology. McGraw-Hill Book Company, New York, N.Y.

Peters, E., 1988. Symbiosis to pathology: are the roles of microorganisms as pathogens of coral reef organisms predictable from existing knowledge? Proc. 6th Int. Coral Reef Symposium, Australia. Vol. 3, 205-209.

Sutton, D.C., Trott, L., reichelt, J.L., and J.S. Lucas, 1988. Assessment of bacterial pathenogenesis in Crown-of-Thorns starfish, Acanthaster planci . Proc. 6th Int. Coral Reef Symp., Australia, Vol. 2, 171-176.

Wilkens, P., 1990. Invertebrates - Stone and False Corals, Colonial Anemones. Engelbert Pfriem Verlag, Wuppertal, Germany.

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