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Related FAQs: Infectious Disease 1, Infectious Disease 2, Infectious Disease 3, Infectious Disease 4, & FAQs on Infectious Disease: Identification, Causes/Etiology, Cures/Medications, Case Histories: Bacterial, True Fungal & Marine Disease 1, Marine Diseases 2Marine Diseases 3, Marine Diseases 4, Marine Diseases 5, Marine Diseases 6Puffer Disease, Clownfish Disease

Related Articles: Understanding Bacterial Disease in Aquarium Fish; With a gallery of bacterial infections, a discussion of 'Fish TB', and a listing of major antimicrobial medications with examples available to fishkeepers By Myron Roth, Ph.D., The Three Sets of Factors That Determine Livestock Health/Disease, A Livestock Treatment System, Treating Parasitic Disease, Using Hyposalinity to Treat Parasitic Disease

Infectious Diseases of Marine Livestock

By Bob Fenner

Eye "Fungus" on a Mono. More likely a secondary bacterial infection

In the past, with poorer capture, holding and transport techniques, infectious disease micro-organisms we're the real scourge of marine aquarium keeping. Whole tanks, even stores would be devastated by the sudden appearance and spread of "velvet" and/or "Ich" with huge losses within days.

Oh how times have changed! Not! Though aquatic livestock may be more vigorous and disease-free on arrival, these same problems are still very much with us. All the fancy gear, decent foods and maintenance will do you no good should these wee-beasties be allowed to enter and reproduce in your system.

To reiterate (Latin for "to journey again"), infectious disease is best controlled by prevention; acquiring clean livestock and running it through a proper acclimation and quarantine procedure. By virtue of their small size and means of respiration, excretion... these animals (and algae) are easily "popped" by dips/baths and freshwater acclimation.

If infection occurs, look to environmental causes and solutions. Lastly, if necessary, remove the specimen(s) to the separate quarantine/treatment tank for isolation and manipulation.


Viral infections are caused by particles that by some definitions are non-living. Virus organisms are only able to metabolically function and reproduce as parasites; using the cellular machinery of their hosts.

Lymphocystis is a viral disease that looks like white to grayish cauliflower-like clumps, typically at the base of fish fins. It's origins, "cures" and spontaneous remission are somewhat mysterious. The condition may just "show up" even in meticulously clean systems.

By itself, Lymphocystis is rarely a damaging or fatal problem. In most cases it "cures" itself by disappearing on the individuals it has "shown up" on in a month or two of it's appearing.

Some authors suggest chemical treatments, biological cleaners, removing the clumpish growths from the fish by scraping with your fingers, even the use of the anti-viral compound Acyclovir. I would suggest isolating "infected" specimens and let them self-correct.


These are microscopic single-celled organisms that can be found in every living environment. There are thousands of species, classified on the basis of structure, nutrition, locomotion and more. Most bacteria are non-infectious to livestock and ourselves; a few are absolutely necessary.

Problems with bacteria are more often a matter of "biological pollution" than outright infection. Allow me to explain. In an artificial environment like a captive marine system, there are little of the "natural checks and balances" of the wild. Filter feeders, predators, dilution by currents... preclude such bacterial population explosions as occur in aquaria. Often the concentration of these microbes is several orders of magnitude that of the oceans.

The difficulty here is that of nutrient use (oxygen, minerals) and metabolic poisoning by these quickly reproducing organisms. Resulting in? Diminished resistance, weakened livestock: disease; either by bacteria or other opportunist. Therefore the premise that under-crowding, proper feeding and maintenance will prevent bacterial problems.

A bacterial infection may be localized or be evident on several areas of an organisms. Bacteria infections are likely to be found in or around open sores or any area where stock has lost it's protective coating.

Virtually all bacterial infections of captive marine life are "secondary"; the result of poor water quality, physical injury, or from some parasitic organism. Always look to poor water quality as the real "cause".

Antibiotics added to make medicated food, or a manufactured line should be used to treat bacteria infections along with frequent water changes. A "dirty" aquarium can prevent successful treatment.

Because there are so many different types of bacteria, you may have to try several types of antibiotics before finding one that works. Be sure to do large water changes between treatments of different medications. Good quality carbon or charcoal, Polyfilter, and Chemipure, among other chemical filtrants will remove medications from the water and should be removed during any treatment with antimicrobials.

Internal bacteria infections are often identified by symptoms; swelling, a fish that has trouble staying on the bottom, whitish feces that float or trail off behind the fish, or lack of feces entirely (blockage).


These simple, plant-like organisms have only started to gain notice for the roles they play in marine environments. Like bacteria, they are mostly benign, and of utmost importance in the wild for their roles in aiding decomposition. Also, akin to the bacteria is their role as infectious agents in aquaria.

Fungal diseases are rare; most are mis-identified bacterial problems, or if truly fungal, the result of a post moribund event; i.e. the specimen is long since dead. Most fungus difficulties are easily avoided by the prophylaxis and non-contamination methods that you've read through here.

If you see a real fungus it will appear to spread evenly, starting from a central point and grow in an outward pattern. Several areas may grow outward until they overlap and give the appearance of a bacteria infection. Fungus is white with a velvety or even hairy appearance. It is most likely to be found on the mouth, eyes, or tips of the fins.

Treatment consists of water changes, medicated food, and sulfonamides. You may find other authors suggesting the use of topical treatments (malachite, dyes, mercuricals...) these are nearly worthless. Once you've detected a true fungus on the surface of an organism it has penetrated below where these medicants will do no good.


In almost all cases, where sufficient preventative measures have been taken, infectious disease only emerges where livestock have been stressed by poor environmental conditions coupled with host susceptibility. Pathogenic (disease-causing) microbes are typically present in marine systems, but are kept non-virulent by conscientious feeding and maintenance practices.

Bibliography/Further Reading:

Blasiola, George C. 1990. Microbial diseases; fungi, bacteria and viruses affect marine aquarium fishes. Pet Age 12/90.

Blasiola, George C. 1993. Tumors in fish; it is hard to distinguish true tumors from growths caused by infection. Pet Age 10/93.

Blasiola, George C. 1995. Fish viruses of aquarium and pond fish. FAMA 10/95.

Dixon, Beverly A. 1990. Bacterial infections in fish. AFM 6/90.

Fairfield, Terry F. 1991. Marine sudden death syndrome, Vibrio anguillarum. FAMA 1/91.

Gargas, Joe. 1994. Bacterial diseases of fish. FAMA 6/94.

Goldstein, Robert J. 1984. Controlling fungi. Pet Age 1/84.

Johnson, Erik L. 1994. Your fishes health; finrot or not? TFH 2/94.

Knight, William A. 1989. Preliminary observation on the treatment of lymphocystis in marine tropical fish. FAMA 7/89.

Sheley, Tom. 1983. Disease prevention and control, part five: bacteria, fungus, virus. FAMA 6/83.

Snieszko, Stanislaus F. & Herbert R. Axelrod, editors. Disease of Fishes: (Book series). T.F.H. Publications, NJ.

____ Bullock, Graham L., David A. Conroy & S.F. Snieszko. 1971, Book 2A: Bacterial Diseases of Fishes. Graham L. Bullock. 2B: Identification of Fish Pathogenic Bacteria.

____ Neish, Gordon A. & Gilbert C. Hughes. 1980. Book 6: Fungal Diseases of Fishes.


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