Flavobacterium columnare (Flexibacter columnnaris) associated with severe gill necrosis in koi carp (Cyprinus carpio L)

Columnaris disease in koi carp

source: A. Decostere et al
Veterinary Record vol 150 no 22, June 1 2002
starts p694, 2 pages long

Columnaris disease is common among edible and ornamental fish found in cold and ornamental waters, and vets need to be able to recognise it and treat it in time, or it can cause heavy losses.

One case involved 25 Japanese koi carp, which were hit by an outbreak in May 2001. Their symptoms included hanging at the surface of the water, listlessness, and lack of appetite. They did not show discolourations or skin lesions. They then started gasping for air and lay side upwards, dying within 48 hours of first showing symptoms. Nine of the koi died during a four-day period. The temperature of the water was 20 deg c, while the pH, oxygen, ammonia and nitrate levels were normal.

The kois’ gills showed an excess of mucusy secretion, visible as yellowish-white areas through all the arches of the gill. Just a slight touch of the gill tissue led to haemorrhage. No parasites were found in the gills or skin, nor were there internal lesions found in post mortems of two euthanased fish. Affected gill tissue was studied by histological examination. There were necrotic cells, and long, slender bacteria in numerous clusters. The gill architecture had totally disappeared in some of the koi. Incubation using Shieh plates revealed F Columnare.

Treatment comprised oxytetracyline added at a dosage of 2.0g per 100 litres during three days, repeating the treatment four days later. An additional two koi died during the first day, but the remaining fish recovered, with an improvement in appetite and activity levels.

This disease has been linked to poor environmental conditions and stress, but this did not appear to be the case with these koi, and it may simply have been an especially virulent strain. There have been comments on the different virulence of strains of F columnare.

It is important to diagnose this disease early on, especially if a virulent strain is involved, since fish that are badly affected usually have to be euthanased, while earlu treatment can save the other fish. F columnare needs special media to grow, and blood agar cannot be used. Vets can spot the typical gill lesions, and can see the filamentous, long, slender bacteria, through microscopial examination of gills. Vets can start treatment before getting confirmation of the disease. Oxolinic acid, nifurprinol, and oxytetracycline have all been successfully used to treat this disease.