General information
Flavobacterium columnare is a gram-negative bacillus. Skin lesions and damage to the epithelium, e.g. due to osmotic skin injury caused by transferring the fish too quickly, are entry points for a so-called columnaris disease in aquarium and pond fish. Poor water quality, high ammonia concentrations, high pH values and low oxygen content promote infection. It mainly occurs in summer when temperatures are warmer.
Initially, small, whitish spots form on the mouth, the edges of the scales and the fins. The edges of the fins begin to disintegrate, exposing the fin rays. Sometimes, there are secondary mycoses at the affected skin areas. The gills can also be affected. In young fish, the gill filaments stick together. This results in rapid breathing. Infections can be chronic or acute, and without appropriate treatment, they are often fatal.