Tilapia Topic: Disease Vector Myxobacteria

Myxobacteria are long slender bacterial rods that are normal flora in tilapia culture systems in Hawaii. A few species of these bacteria are pathogenic to fish including tilapia. Susceptible fish are usually under stress or the bacteria invade surface wounds or abrasions. When tilapia are crowded myxobacteria may attack the gills resulting in periodic low level or acute high level mortality.

Diagnosis

Tilapia affected by myxobacterial disease (a.k.a. columnaris disease) may display signs of respiratory distress and/or have opaque, slightly raised white, irregular patches on the head, mouth, body or fins. When gills are infected variable sized areas of gill tissues will be opaque and have the appearance of rotting tissue. Wound infections are not uncommon.

The species of myxobacteria associated with infections in tilapia in Hawaii have not been described. However, some isolates are similar to Flexibacter spp. and probably several genera and species are involved in myxobacterial infections of tilapia cultured in Hawaii. Isolation of these bacteria requires the use of special media (Cytophaga Agar) and application of biochemical and morphological bacteriology procedures.

Myxobacteria are long (0.003-0.1mm), thin (0.0005 mm), rod shaped bacteria that are often seen in clumps or "stacks" in microscopic examination of wet-mounts (high-dry, 400X to oil-immersion, 1,000X) of surface lesions infected by these bacteria. In wet-mounts some myxobacteria will be seen to move by a flexing or gliding motion.

Prevention

Prevention of myxobacterial disease in tilapia by application of good husbandry practices is usually effective.

See:

• Bacteria Vectors

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