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		Vibrio Infections of Fish
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		Signs of Infections The signs of vibriosis are similar to many other bacterial diseases of fish. They usually start with lethargy and a loss of appetite. As the disease progresses, the skin may become discolored, red and necrotic (dead). Boil-like sores may appear on the body, occasionally breaking through the skin surface resulting in large, open sores. Bloody blotches (erythema) are common around the fins and mouth. When the disease becomes systemic, it can cause exopthalmia ("pop-eye"), and the gut and rectum may be bloody and filled with fluid. It should be noted that all of these "signs" can be caused by other bacterial diseases, and are not proof of a Vibrio infection. Diagnosis Although a Vibrio infection can be suspected given certain case histories and clinical signs, proper diagnosis requires isolation of the bacteria and its identification. If you are unable to perform these tasks yourself, live, diseased fish should be delivered to a diagnostic laboratory familiar with fish diseases to confirm the infection, identify the species of Vibrio , and perform an antibiotic sensitivity test. Contact your county extension agent for assistance on where and how to submit samples for diagnostic services. For those who are capable of culturing bacteria, Vibrio spp. prefer a blood agar supplemented with 3% salt, but enriched media such as trypticase soy agar with 5% ovine blood is adequate for initial isolation. Vibrio spp. can be differentiated from closely related bacteria by its specific sensitivity to Novobiocin and 0/129, two commercially available vibriostatic agents. Despite the unique "comma-shape" of Vibrio bacteria, microscopic examination of infected tissues cannot be used in place of culture and isolation techniques. Transmission The precise route of Vibrio infection is unclear, but oral transmission is suspected. It is possible to isolate Vibrio spp. from the intestinal tract of clinically normal fish. Under certain conditions, the bacteria may be capable of crossing the intestinal wall, resulting in systemic disease. Once an outbreak is in progress, the number of infectious particles in the environment rises dramatically, increasing the chance that exposed fish will get sick. Management In confined, heavily stocked, commercial systems, Vibrio disease outbreaks can proceed rapidly. Therefore, prevention is essential to any management scheme. As Vibrio species are believed to be opportunistic, conditions which favor a disease outbreak are often caused by environmental stress which can be avoided. Poor nutrition or water quality, improper handling, overcrowding, and the presence of other disease-causing agents will all increase your fish's chances of contracting a Vibrio infection. Parasites are of special concern, as they often cause damage to fish tissue, creating an ideal location for Vibrio infections to begin. Chemical treatments, including the use of copper compounds, can be harsh on fish and have been reported to precipitate Vibrio disease outbreaks. Quarantine of new fish and good sanitation practices should be used at all times, and will minimize the spread of Vibrio infection from infected to uninfected fish, should a disease outbreak occur. New fish should always be kept away from existing fish. Tanks and culture facilities should be kept clean and free of any unnecessary wastes. more ...

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