Columnaris

The bacteria are ubiquitous in fresh water, and cultured fish reared in ponds or raceways are the primary concern – with disease most prevalent in air temperatures above 12–14 °C.

[1] The bacteria usually enter fish through gills, mouth, or small wounds, and is prevalent where high bioloads exist, or where conditions may be stressful due to overcrowding or low dissolved oxygen levels in the water column.

Signs of acute disease may manifest in the form of shortness of breath, gill discolouration, and itching as indicated by flashing, quick movements of a fish rubbing skin against other surfaces.

Lesions begin at the base of the dorsal fin on the back of a fish and spread over time, hence the name saddleback disease.

Ulcerations on the skin, and subsequent epidermal loss, identifiable as white or cloudy, fungus-like patches – particularly on the gill filaments, may appear.

[3] Definitive diagnosis is usually made from bacteria isolated from gills or skin cultured using low nutrient growth media kept between 25 and 30 °C.

Potassium permanganate, copper sulfate, and hydrogen peroxide can also be applied externally to adult fish and fry, but can be toxic at high concentrations.

He was unsuccessful in culturing the disease artificially but acknowledged that "Bacillus columnaris is widely distributed over the country" being most deadly during warm weather and to fish already injured in some way.