Overview of Aquarium Fishes

Aquatic medicine has emerged as a recognized specialty within the practice of zoologic medicine. Fish medicine, an important component of the aquatic specialty, is evolving, with distinct subspecialties of aquaculture and production medicine (see Aquaculture) 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 fishes, which includes specimens that may be added to zoologic collections, can be broadly divided into freshwater and marine species. Most pet fishes are freshwater, and many are farm raised in the USA, Asia, or elsewhere. Many fish sold through the pet trade are imported to the USA. Except for a small number of species such as some clownfishes (Amphiprion spp), dottybacks (Pseudochromis spp), gobies (primarily Elacatinus spp), blennies (primarily Meiacanthus spp), and seahorses (Hippocampus spp), most marine fishes are wild caught. The trade in ornamental fishes is a global industry, and fishes are often moved through several dealers before reaching a wholesale or retail outlet. The source of these fishes 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 and bacterial infection 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 significant emotional value to their owners. These fish are susceptible to several diseases of regulatory concern, most notably spring viremia of carp and koi herpesvirus, which are both reportable diseases.

Clinical management of individual pet fish, exhibit animals, and valuable broodstock has changed dramatically in recent years. Advances include use of nonlethal methods to diagnose disease and more sophisticated treatment options. Radiology and ultrasound are particularly well suited for use in aquatic species, as are CT and MRI. They are especially valuable for evaluation of the gas bladder, investigation of internal masses, and more. Development of blood culture techniques to accurately identify bacterial agents and perform susceptibility tests before starting antibiotic 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 cover slips, basic surgical or dissecting tools), water quality parameter testing equipment is needed (see Aquatic Systems).

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 radiology, 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 fishes are susceptible to several reportable diseases, which include spring viremia of carp (see Rhabdoviruses : Spring Viremia of Carp (SVC)), koi herpesvirus (see Koi Herpesvirus), epizootic ulcerative syndrome (see Aquarium Fishes:Oomycota), and red sea bream iridovirus (see Iridoviruses : Megalocytiviruses).