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High Mortality in Zebrafish (Danio rerio)
Jennifer K. Pullium1, Dirck L. Dillehay, Sonji Webb
1Division of Animal Resources, Emory University, School of Medicine, Atlanta, GA 30322.
Contemporary Topics in Laboratory Animal Science
|June 28, 2002
Summary
High stocking density and toxic nitrite levels in new zebrafish housing systems led to motile aeromonad septicemia (MAS). Improving water quality and reducing fish density resolved the outbreak, highlighting the importance of proper system cycling and stocking density for fish health.
Area of Science:
- Aquatic animal health
- Fish pathology
- Microbiology
Background:
- Zebrafish are crucial models in biomedical research.
- Maintaining optimal water quality is essential for fish health in aquaculture systems.
- Newly established or improperly cycled aquaculture systems can harbor water quality issues.
Purpose of the Study:
- To investigate the cause of a disease outbreak in a new zebrafish housing system.
- To identify the etiological agent and contributing factors to the observed pathology.
- To provide recommendations for preventing future disease events.
Main Methods:
- Histopathological examination of affected zebrafish tissues.
- Bacterial and fungal cultures from fish and water samples.
- Water quality parameter analysis (pH, ammonia, nitrite).
Main Results:
- Petechial hemorrhages and skin ulcerations were observed in affected fish.
- Aeromonas hydrophila and A. sobria were isolated, leading to a diagnosis of motile aeromonad septicemia (MAS).
- Toxic nitrite levels (1-5 ppm) indicated poor water quality due to insufficient nitrifying bacteria colonization.
Conclusions:
- Inadequate cycling of the new housing system resulted in high nitrite levels and overcrowding-induced stress.
- These factors compromised zebrafish immunity, increasing susceptibility to MAS.
- Reducing stocking density and improving water quality resolved the septicemia outbreak.