9428 ‎(2)‎

• UCREFRP Catalog Number: 9428
• Author: Erdahl, D. A.
• Title: Inland Salmonid Broodstock Management Handbook.
• USFW Year: no dat
• USFW - Doc Type: Bozeman.
• Copyright Material: NO

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