The fish practitioner may encounter a new fish owner who brings their pet to the veterinary office as a beloved member of the family or a client with an ornamental backyard fishpond. As compared to land-dwelling animals, fish patients have the added challenge that their water environment plays a critical role in their health. An assessment of the patient's neurological status should be performed prior to induction of anesthesia. The mouth of each patient should be opened and examined with a light source. Good sample selection, especially in population health–type evaluations where disease prevalence can be low, is critical. Fish may also exhibit other characteristic signs of disease. The general history should focus on determining what species are affected, what clinical signs have been appreciated by the client and the time course of the disease. Numerous factors will guide the clinician's approach to disease diagnostics for each case.