Several emerging infectious diseases have serious implications for the trade and husbandry of ornamental fish. Although many of these diseases have been well studied and described in certain species, there are still many diseases that are not well understood. The following discussion focuses on select important emerging infectious diseases that affect ornamental fish in the aquarium and aquaculture industries: goldfish herpesvirus, koi herpesvirus, Ranavirus, Megalocytivirus, Betanodavirus, Francisella, Cryptobia iubilans, and Exophiala. When possible, the known species affected, clinical signs, diagnosis, treatment, disinfection, and prevention modalities for each disease are discussed.