Flexibacter columnaris (Columnaris disease or Saddleback disease)
A. Gram-negative slender rods (3-8 microns)
B. The disease is a serious disease of young salmonids, catfish and many other fish.
C. This is a highly communicable disease. Lesions usually first appear as small white spots on the caudal fin and progresses towards the head. The caudal fin and anal fins may become severely eroded. As the disease progresses, the skin is often involved with numerous gray-white ulcers. Gills are a common site of damage and may be the only affected area. The gill lesions are characterized by necrosis of the distal end of the gill filament which progresses basally to involve the entire filament.
D. Flexibacter columnaris infections are frequently associated with stress conditions. Predisposing factors for Columnaris disease are high water temperature (25oC-32oC.), crowding, injury, and poor water quality (low oxygen and increased concentrations of free ammonia).
E. Flexibacter maritimus: cause similar problems in salt water environment.
F. Flexibacter psychrophilus causes Cold Water Disease or Peduncle disease. Fish develop dark skin, hemorrhage at the base of fins, and anemia with pale gills with increase mucus. Hemorrhage into the muscles is common. Periostitis of cranial and vertebral bones is common in chronic cases. Chronic meningoencephalitis occasionally is observed with abnormal and erratic swimming.