Aquatic medicine has emerged as a recognized specialty within the practice of zoological medicine. Fish medicine, an important component of the aquatic specialty, is evolving, with distinct subspecialties of aquaculture Aquaculture and production medicine as well as pet and exhibit fish medicine that focuses on individual animals. This chapter focuses on pet and exhibit fish medicine.
The business of ornamental fish, which includes specimens that may be added to zoological collections, can be broadly divided into freshwater and marine (as well as brackish) species. Most pet fish are freshwater, and many are farm raised in the US, Asia, or elsewhere. Many fish sold through the pet trade are imported to the US. Except for a small number of species, such as some clownfish (Amphiprion spp), dottybacks (Pseudochromis spp), gobies (primarily Elacatinus spp), blennies (primarily Meiacanthus spp), and seahorses (Hippocampus spp), most marine fish are wild-caught.
The trade in ornamental fish is a global industry, and fish are often moved through several dealers before reaching a wholesale or retail outlet. The source of these fish is an important consideration when designing quarantine protocols and anticipating the types and severity of disease that may be seen in recently acquired animals. Some fish species, whether marine or freshwater, are particularly prone to parasitic Parasitic Diseases of Fish All of the major groups of animal parasites are found in fish, and apparently healthy wild fish often carry heavy parasite burdens. Parasites with direct life cycles can be important pathogens... read more 
and bacterial infection Bacterial Diseases of Fish Epidemics of bacterial diseases are common in dense populations of cultured food or aquarium fish. Predisposition to such outbreaks frequently is associated with poor water quality, organic... read more 
during the quarantine period (first 30 days), including the first few weeks after arrival in a pet store or home aquarium.
Cyprinids such as koi and fancy goldfish for ornamental ponds are popular pets and typically respond well to veterinary care. Many of the highest quality are imported from Japan (koi) or China (fancy goldfish) and may have significant value (up to several thousand dollars for show-quality koi). Many are large enough for clinical manipulation, are quite hardy, and often have important emotional value to their owners. These fish are susceptible to several diseases of regulatory concern, most notably spring viremia Spring Viremia of Carp (SVC) Descriptions of viral diseases of fish are rapidly expanding. Viruses are being reported in new species, and interpretation of the significance of findings is also changing. Several viral diseases... read more 
of carp and koi herpesvirus Koi Herpesvirus Descriptions of viral diseases of fish are rapidly expanding. Viruses are being reported in new species, and interpretation of the significance of findings is also changing. Several viral diseases... read more , which are both reportable diseases.
Clinical management of individual pet fish, exhibit animals, and valuable broodstock has changed dramatically over time. Advances include use of nonlethal methods to diagnose disease and more sophisticated treatment options. Radiography Radiography of Animals Radiography (generation of transmission planar images) is one of the most commonly used diagnostic tools in veterinary practice even though other imaging modalities such as ultrasonography,... read more 
and ultrasonography Ultrasonography in Animals Ultrasonography is the second most commonly used imaging format in veterinary practice. It uses ultrasonic sound waves in the frequency range of 1.5–15 megahertz (MHz) to create images of body... read more are particularly well suited for use in aquatic species, as are CT Computed Tomography in Animals In computed tomography (CT), an x-ray tube moves around the body and continuously projects a thin fan of x-rays through the body. Electronic detectors opposite the tube continuously monitor... read more 
and MRI Magnetic Resonance Imaging in Animals Magnetic resonance imaging (MRI) is the newest form of imaging in general use today. In this imaging modality, a powerful magnet, up to 60,000 times as strong as the magnetic field of the earth... read more 
. They are especially valuable for evaluation of the gas bladder, investigation of internal masses, and more. Development of techniques for microbial culture of blood to accurately identify bacterial agents and perform susceptibility tests before starting antimicrobial therapy has been useful to decrease the need to euthanize, or surgically biopsy, an animal to achieve an accurate diagnosis. Surgical advances, including use of exploratory laparotomy and gas bladder repairs, have salvaged animals that previously would have been euthanized.
The equipment needed to treat fish in a veterinary practice is modest. In addition to equipment already on hand (eg, microscope, glass slides and coverslips, and basic surgical or dissecting tools), water quality parameter testing equipment Equipment Needed for Aquatic Systems and Water Analysis To competently assess a system’s design takes some practice; however, basic understanding and analysis can be accomplished by examining the component parts and their functions. Site visits are... read more is needed.
In addition to these basic tools, a practice should have a few fish tanks for use as hospital systems. These can be 10- or 20-gal. tanks with simple foam filters and aeration pumps. A dechlorinator such as sodium thiosulfate should be on hand if the practice uses water that contains chlorine or chloramine. In addition, tricaine methanesulfonate (MS-222) and baking soda should be available for sedation or anesthesia.
Other useful equipment includes a 1-L plastic graduated cylinder for measurement of water volume, a balance to weigh out anesthetic, and a battery-powered aeration pump if an anesthetized fish is to be moved around the clinic for radiography, surgery, or other procedures. For surgery, a 10- to 20-gal. tank works well as a receptacle. An egg crate lighting panel, or a plexiglass or plastic cover with small holes drilled in it, can be placed over the tank to allow water to flow over the fish and back to the tank. The fish can be positioned in a V-shaped foam bed, and a small, submersible aquarium pump and flexible tubing can be used to circulate anesthetic-treated, aerated water out of the tank and over the gills. Use of equipment that can be sterilized after each patient is advantageous.
Veterinarians who offer fish medicine should be aware of evolving regulatory concerns, including the current USDA accreditation programs. In addition, aquarium fish are susceptible to several reportable diseases, which include spring viremia of carp Spring Viremia of Carp (SVC) Descriptions of viral diseases of fish are rapidly expanding. Viruses are being reported in new species, and interpretation of the significance of findings is also changing. Several viral diseases... read more , koi herpesvirus Koi Herpesvirus Descriptions of viral diseases of fish are rapidly expanding. Viruses are being reported in new species, and interpretation of the significance of findings is also changing. Several viral diseases... read more , epizootic ulcerative syndrome Epitheliocystis Epidemics of bacterial diseases are common in dense populations of cultured food or aquarium fish. Predisposition to such outbreaks frequently is associated with poor water quality, organic... read more , and red sea bream iridovirus Megalocytivirus Descriptions of viral diseases of fish are rapidly expanding. Viruses are being reported in new species, and interpretation of the significance of findings is also changing. Several viral diseases... read more .
