Special Procedures for Zebrafish Diagnostics

Abstract Zebrafish are small fish that live in small aquaria, which provides both advantages and challenges for pathogen monitoring and diagnostics. Fish are intimately linked to their aquatic environment, and hence, suboptimal water quality parameters or the presence of toxicants are important causes of disease in zebrafish. Therefore, evaluation of water quality is central to a disease investigation and health monitoring. Histopathology is often the primary or first-line diagnostic test for zebrafish. A major strength of histopathology is that it facilitates the documentation of changes in a variety of tissues and organs with no a priori assumptions relating to a specific disease, and the small size of the fish allows for examination of essentially all organs on one slide using sagittal sections of whole fish. Immunohistochemistry has been utilized in diagnostics. However, most antibodies were created to mammal antigens, and thus, results should be interpreted with caution. PCR tests have been developed for important zebrafish bacteria and parasites, and these are used for evaluating fish tissues as well as environmental samples (e.g., water, feces). Whereas commonly used in food fish aquaculture, therapeutants are rarely used with zebrafish. Examples include oral treatments for nematodes and mycobacteria and drugs delivered in the water for external parasitic infections and intestinal nematodes. Laboratory veterinarians have new opportunities and challenges with the increased use of laboratory zebrafish. When compared with rodents, disease diagnosis and management of aquatic species requires a different approach due to their housing environment. As fish live in water, they are intimately affected by inappropriate water quality parameters. Moreover, the transmission of waterborne pathogens between tanks may be a serious problem with recirculating water systems. Because of the unique housing environment of aquatic species, disease evaluation should always include a thorough history, a review of environmental parameters (i.e., water quality, light cycles, vibrations/noise), as well as diagnostic testing. In this chapter, we will review disease diagnosis utilizing both live animal and environmental samples and options for treatment of disease.