Bacterial diseases

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'Cotton mouth' in an aquarium fish caused by Flavobacterium columnare

Bacterial diseases are responsible for heavy mortality in both wild and cultured fish. The actual role of these micro-organisms may vary from that of a primary pathogen to that of an opportunist invader of a host rendered moribund by some other disease process[1].

Many of these organisms are a usual component of the bacterial flora in aquatic habitats, particularly eutrophic systems. Stressors, often inevitable in most culture systems, predispose fish to bacterial-born diseases[2]. The course of events from stress to predisposition to infection, include physiological changes (described as a general alarm response syndrome) the consequences of which are to enforce barriers, normally preventing entry of bacteria to fish inner systems and at the same time incapacitating fish defence responses and immune reactions[3].

Common bacterial diseases in fish include:


  1. Richards, R.H. & Roberts, R.J., (1978) The bacteriology of teleosts. In: Roberts, R.J. (ed.) Fish Pathology. Bailliere, Tindall, London. pp:183–204
  2. Snieszko, S.F., (1974) The effect of environmental stress on outbreaks of infectious diseases of fishes. J Fish Biol 6:197–208
  3. Barton, B. A. & Iwama, G.K., (1991) Physiological changes in fish from stress in aquaculture with emphasis on the response and effects of corticosteroids. Annual Rev Fish Dis 1:3–26