Laserfiche WebLink
Causes of Fish Diseases <br />Fish diseases do not occur as single caused events, but are the <br />result of interactions between the pathogen, the fish (host), and <br />the environment. Even if a pathogen is present, serious disease <br />outbreaks seldom occur if environmental quality is maintained. For <br />example, although fish pathogens such as Aeromonas, Pseudomonas, <br />and Mvxobacteria spp. are continuously present in most hatchery <br />water supplies, epizootics rarely occur if environmental quality <br />is not allowed to deteriorate. It is when the presence of a <br />pathogen(s) is combined with a stressful environment that a disease <br />outbreak is likely to result (Figure 2A). <br />STRESSFUL COMFORTABLE NO <br />DISEASE ENVIRONMENT ENVIRONMENT DISEASE <br />OCCURS <br />PATHOGEN HOST PATHOGEN HOST <br />FIGIIRE 2A. Interaction Between Pathogen, Fish (Host), and <br />Environment (Source: Rapuscinski and Gross, 1986). <br />Intensively reared fish are continuously stressed by environmental <br />conditions and management practices such as fluctuating water <br />temperatures, changes in water quality, crowding, handling, drug <br />treatment, and transport. Fish can handle these stresses up to a <br />given point but when the cumulative effect exceeds homeostatic <br />tolerance limits, disease and eventual death is often the result. <br />2-2 <br />