Pet fish are one of the most numerous companion animals in U.S. households, yet few fish owners consult veterinarians about fish disease partly because historically veterinarians have declined to offer them assistance. Yet all veterinarians are trained in pathology, diagnostics, animal husbandry, and pharmacology, so who better to apply the principles of these disciplines to pet fish.
The basic approach to evaluating a pet fish is similar to that of evaluating mammals, birds, reptiles, and amphibians, though fish medicine requires a few unique diagnostic methods, such as performing water quality tests and collecting special samples for wet mount preparations.
You can diagnose most fish diseases by using a high-quality microscope that has 10X, 40X, and 100X (oil immersion) objectives.
The ability to test water quality is also important. Inexpensive semiquantitative water quality test kits (e.g. Marine Enterprises International, Baltimore, Md.; Tetra, Blacksburg, Va.) provide a general indication of the various water quality parameters. The more expensive test kits (e.g. Aquaculture Multi-Parameter Test Kit, Model FF-1A or FF-2—Hach, Loveland, Colo.) are more accurate and appropriate for diagnostic testing of water quality. In addition, a number of electronic probes are available for monitoring temperature, pH, dissolved oxygen, chloride, and conductivity (salinity). These probes tend to be expensive and need to be properly calibrated.
Aquariums of various sizes (10 gal for small fish, 150-gal stock tanks for larger fish such as koi), clear buckets (5 and 10 gal), fish nets in various sizes, air pumps with air stones, small filtration systems, a water pump for anesthetic delivery, sodium thiosulfate to remove chlorine from water, and tricaine methanesulfonate (MS-222; Finquel—Argent Chemical Laboratories, Redmond, Wash.) for anesthesia are also needed to care for fish.
TRANSPORTING THE FISH
Before clients bring fish to your hospital, advise them about proper transportation. Fish should be transported in a container filled with water that varies little in quality and temperature from that of the fish's normal habitat. Ask the owner to bring a water sample (at least 120 ml [4 oz]) from the habitat in a separate sealed container for water quality testing. For meaningful results, test the water within one hour of collection. Poor water quality is the most common cause of disease in pet fish, so water quality testing is crucial (see boxed text titled "Identifying and correcting water problems").
Identifying and correcting water problems
To obtain a thorough history, learn about the owner's level of expertise in keeping fish, the current problems a fish is having, any past problems, and the overall husbandry provided. Important husbandry information includes the size of the aquarium or pond; the animal population of the aquatic system; the water temperature, filtration type, and aeration method; and the quality and quantity of light. Abnormal photoperiods, such as prolonged light, can cause chronic stress and add to other stressors that may be affecting the aquatic inhabitants. A photoperiod that matches the natural environment of the animals is best. Full-spectrum lighting is more important to the plants in the aquatic system; however, light intensity should match that of the animal's natural environment, if that information is available. Also ask the owner about the water quality, diet, quarantine practices, and current and previous treatments.
Before performing a hands-on physical examination, it is best to examine the fish in the aquarium or pond, if possible, or in the transport container. Observe the activity and body language of the fish in the water. It is important to know the normal behavior of the species of fish being evaluated. For example, male bettas (Betta splendens) are often kept in small bowls without filtration or temperature control. They normally use the midlevel or upper level of the bowl; however, when the temperature drops too low, they sit on the bottom and are reluctant to move. Also, the foraging behavior of certain fish may be confused with abnormal behavior.