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Columnaries Disease
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External Signs of Columnaris
Fish infected with columnaris usually show signs which can be recognized by the fish farmer before fish start to die. Ulceration of the skin or erosion of fins are the most obvious early signs. In scaled fish, the fins are often the first site of infection. Fins appear more ragged as the condition worsens, and fungal infection may become established in areas of dead tissue. A presentation such as this, with ragged, fungus-infected fins, is commonly described as "tail rot." Columnaris is not the only cause of tail rot, however.

In nonscaled fish, such as channel catfish, infection frequently starts on the skin along the lateral body wall or behind the dorsal fin. Infected skin can be recognized because it appears off-color, most commonly taking on a pale gray hue. Initially, the off-color area will be very small, but if unchecked, the infection will spread becoming wider and deeper, until in severe cases, the underlying musculature is exposed. In the most severe cases, the ulceration may be so deep that the backbone is visible. Fungal infections frequently occur in ulcerated areas giving the lesion a fuzzy brown appearance. Fish affected with this type of lesion are said to have "saddleback disease", and this is very typical for channel catfish infected with columnaris.

Some fish infected with columnaris never develop the skin lesions described above. The gills may be severely infected, however, causing the fish to show signs of oxygen stress. This condition can be discovered by lifting the operculum and examining the gill filaments. Gill tissue infected with columnaris will be severely decayed and large areas of gill filaments may be missing, exposing the cartilaginous gill arch. This can be distinguished from many parasitic diseases because most parasites cause irritation rather than evident decay of tissue, resulting in excess mucus production and causing the gills to appear swollen. Fungal infections commonly occur on gill filaments, secondary to bacterial infection, and appear as a brown fuzzy material on remaining tissue. Fish affected with columnaris would not be expected to have a distended abdomen ("dropsy"), bloody fins, or protruding eyes ("popeye"), unless an internal infection were complicating the disease. Mixed infections are common with columnaris so care must be taken to note these signs if they are present.


Internal Signs of Columnaris
Classic columnaris disease is considered an external infection, however systemic (internal) infection is a common complication. Non-specific signs of internal infection include pale internal organs with small bloody spots on them. The presence of fluid in the gut or abdomen may be suggestive of bacterial infection. The only way to know if an internal infection is complicating the fishes' recovery is to culture the internal organs, preferably the posterior kidney.


Sample Submission
A diagnosis of external columnaris infection can be made with a microscope, however, a bacterial culture of internal organs is recommended to determine antibiotic sensitivity and to identify any other bacteria which may be contributing to the disease outbreak. An examination for external parasites is also recommended because a parasite problem could complicate recovery or contribute to poor treatment results.

With a little practice, most fish farmers can learn to use a microscope to identify columnaris bacteria on skin or gills, as well as external parasites. Professional assistance is recommended for identification of bacteria cultured from internal organs and for antibiotic sensitivity tests. Live, sick fish can be packed on ice and sent to a diagnostic laboratory for this work.


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