{"id":1543917,"date":"2026-03-17T11:54:51","date_gmt":"2026-03-17T10:54:51","guid":{"rendered":"https:\/\/laboklin.com\/new-diagnostic-tests-for-fish-and-reptiles\/"},"modified":"2026-06-01T13:33:09","modified_gmt":"2026-06-01T11:33:09","slug":"new-diagnostic-tests-for-fish-and-reptiles","status":"publish","type":"post","link":"https:\/\/laboklin.com\/dk\/new-diagnostic-tests-for-fish-and-reptiles\/","title":{"rendered":"New Diagnostic Tests for Fish and Reptiles"},"content":{"rendered":"

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Columnaris disease in koi and aquarium fish<\/h2>\n

The causative agent of columnaris disease is Flavobacterium columnare<\/em>, a bacterium that plays a particularly important role in the ornamental fish trade. Flavobacterium columnare <\/em>is a Gramnegative, rod-shaped bacterium measuring 5\u201312 \u00d7<\/p>\n

0.5 \u00b5m. It exhibits slow gliding motility but lacks flagella. Flavobacterium columnare <\/em>has been detected in popular aquarium fish species such as neon tetra (Paracheirodon innesi<\/em>), platy (Xiphophorus maculatus<\/em>) and zebrafish (Danio rerio<\/em>), as well as in pond fish such as koi (Cyprinus carpio<\/em>). In principle, the pathogen can occur in all freshwater fish; however, outbreaks in pond fish are most common during the summer months when water temperatures are higher. Entry points for the pathogen are skin lesions. Infection is further promoted by poor water quality, high ammonia concentrations, elevated pH, and low oxygen levels. Initially, small whitish lesions develop around the mouth, fin margins, and scales, which resemble fungal growth as they enlarge. In scaleless fish such as channel catfish (Ictalurus punctatus<\/em>), the infection begins as small bluish-grey necrotic lesions in the skin with a reddish inflammatory margin.<\/p>\n

Microscopically, large numbers of F. columnare <\/em>bacteria can be detected both in the centre and at the wound margins, with the edge often appearing to consist almost entirely of bacterial cells. In fish with scales, lesions may begin at the outer fin margins and spread inwards across the body, giving a saddle-like appearance. This is the origin of the term \u201csaddleback disease\u201d. Initially, degradation of the fin edges occurs, leaving the fin rays exposed.
\nThe gills may also be affected. In such cases, the gill lamellae disintegrate from the tips towards the gill arches. In juvenile fish, excessive swelling of the gill epithelium and increased mucus production often lead to adhesion of the gill lamellae.
\nThe consequence is reduced oxygen uptake, resulting in rapid respiratory movements.<\/p>\n

Two clinical forms of columnaris disease can be distinguished. In the chronic form, white lesions enlarge slowly and fish die only after a prolonged course of disease. In the acute form, skin lesions spread within hours. Up to 50% of a fish population may die within 36 hours. In experimental infections in zebrafish, characteristic dorsal lesions have been observed as early as 24 hours post infection. Treatment must therefore be initiated rapidly.<\/p>\n

Antibiotic treatment based on antibiogram results is generally possible. However, it should always be combined with optimisation of husbandry conditions. As the pathogen prefers an alkaline environment, lowering the pH to 6.8 may support treatment. For diagnosis, a swab is taken from affected body areas. This can be examined both by culture and by PCR. On Anacker\u2013Ordal agar, F. <\/em>columnare <\/em>grows as pale yellow colonies at 18\u201330 \u00b0C (Fig. 1), with a tendency to adhere to the agar surface. At temperatures below 14 \u00b0C and above 33 \u00b0C, no growth occurs under culture conditions.[\/vc_column_text][\/vc_column][vc_column width=”1\/3″][vc_column_text css=””]<\/p>\n\n\t\t\t