Fish Pathology and Health

(Source: J. Matthews from Zebrafish Book 5th Edition)

Most disease problems in zebrafish can be avoided by utilizing good quarantine practices and maintaining optimal environmental conditions.  Many infectious organisms are opportunistic in nature and are a normal part of the aquatic ecosystem.  Under optimal rearing conditions, fish can co-exist with these pathogens in the aquatic environment.  If stress or unfavorable husbandry conditions occur, the natural defense mechanisms of the fish become weakened and fish then become susceptible to disease.  Outbreaks of disease often occur following some type of environmental stress such as shipping, over crowding, or poor water quality.

Knowing the history of fish acquisitions and quarantine procedures for a facility is important in the evaluation of a disease outbreak.  If only surface sanitized embryos have been brought into a facility a large number of pathogens, particularly parasites, can be considered unlikely.  Zebrafish acquired from local aquarium stores and bulk commercial suppliers, on the other hand, should be considered at high risk for harboring pathogens.

Diagnostic Procedures

Environmental Evaluation

Environmental factors often play a significant role in the development of disease in fish.  Evaluating water quality parameters is an essential initial step when investigating any case of sick or dying fish.  There are numerous aquarium hobbyist-grade or professional quality (e.g. LaMotte) test kits on the market that are inexpensive and provide accurate results.  In all diagnostic evaluations temperature, pH, ammonia and nitrite should be measured, at least.  Additional parameters may include dissolved oxygen, gas saturation, chlorine/chloramines, salinity, nitrate, hardness, metals or others depending on the situation.  Some general recommendations for basic water quality and husbandry parameters in laboratory zebrafish systems are listed below.  Sudden changes in water quality parameters can be very stressful on fish, and should be avoided.

*  ^oH=17.9 mg/l as CaCO₃

Clinical Exam

Diagnostic procedures most often require the sacrifice and sampling of individual fish.  It is possible to carry out a limited exam on a living, usually anesthetized, specimen.  Post-mortem procedures can include skin scrapings, fin and gill biopsies, bacteriology and histopathology.  Histopathology is a very useful diagnostic technique.  The small size of zebrafish allows them to be fixed and sectioned as whole mounts.  This permits the examination of all the primary organ systems on a single microscope slide.  Diagnostic procedures for zebrafish are described in detail in the on-line manual, "Diseases of Zebrafish in Research Facilities." available at [http://zebrafish.org/zirc/health/diseaseManual.php.]

ZIRC Diagnostic Pathology Services

The Zebrafish International Resource Center (ZIRC) provides diagnostic pathology services and consultation on health and husbandry issues related to laboratory zebrafish.  The diagnostic services can be utilized to analyze suspected disease problems or for routine sentinel or quality control testing of laboratory zebrafish colonies.  Services include histopathology, bacteriology and necropsy exam. For more information, see [http://zebrafish.org/zirc/health/index.php.]

Additional Reading

Astrofsky, K. M., Harper, C. M. Rogers, A. B., and Fox, J. G. (2002a).  Diagnostic techniques for clinical investigation of laboratory zebrafish.  Lab Animal 31, 41- 45.

Trevarrow, B. (2005).  Zebrafish facilities for small and large laboratories.  In "The Zebrafish: 2nd Edition Genetics, Genomics and Informatics.  Methods in Cell Biology, vol. 77," (H.W. Detrich, M. Westerfield and L.I. Zon, eds.), pp. 565-591.  Elsevier Inc., San Diego.

Matthews, J.L. (2005).  Common diseases of laboratory zebrafish.  In "The Zebrafish: 2nd Edition Genetics, Genomics and Informatics.  Methods in Cell Biology, vol. 77," (H.W. Detrich, M. Westerfield and L.I. Zon, eds.), pp. 617-643.  Elsevier Inc., San Diego.