columnare

Columnare, also known as columnaris disease, is an infectious disease of freshwater fish caused by the bacterium Flavobacterium columnare. It affects a wide range of species and can cause significant mortality in aquaculture, ornamental fish setups, and natural systems when conditions are favorable for disease development.

Causative agent and ecology: Flavobacterium columnare is a Gram-negative, rod-shaped bacterium that thrives in aquatic environments and can form biofilms on surfaces and mucosal tissues. The disease is more likely to appear under warm water temperatures, high organic loads, crowding, and other stresses that compromise fish immunity. The pathogen can persist in water, on equipment, and in carriers, facilitating transmission.

Transmission and risk factors: Transmission occurs through contaminated water, infected or carrier fish, and contact with contaminated equipment or surfaces. Stressful conditions such as poor water quality, rapid temperature fluctuations, and overstocking increase susceptibility and disease spread. Ornamental fish and young stock are commonly affected in hatcheries and hobbyist aquariums.

Clinical signs and pathology: Infected fish may show cotton-like or grayish lesions on the skin, fins, mouth, or gills. Affected gills can become necrotic, leading to respiratory distress, while skin lesions may progress to ulcers. Disease can be acute with rapid decline or persist chronically in stressed populations.

Diagnosis: Diagnosis relies on clinical signs and observation of characteristic lesions, supported by laboratory confirmation through bacterial culture on selective media or molecular methods such as PCR.

Treatment and control: Treatment typically involves antimicrobial therapy under veterinary or professional guidance, combined with measures to improve water quality and reduce stress. Common strategies include isolating affected fish, maintaining clean and well-oxygenated water, and minimizing crowding. Prevention focuses on quarantine of new stock, consistent water quality management, proper disinfection of equipment, and monitoring for early signs of disease.