This chapter provides the aquatic animal veterinarian information and context to make decisions about pharmaceutical treatments for fish species. It discusses legally marketed products for food fish in the United States under the US Food and Drug Administration (FDA) Center for Veterinary Medicine. The chapter addresses drugs and regulations in the European Union, Norway and Canada and also discusses treatments in ornamental and tropical fish species. The FDA's “Letter to Aquaculture Professionals” details the benefits of FDA approvals for drugs and medicated articles for food fish. Drugs and/or medicated articles have been approved to treat aquatic species for bacterial gill disease, columnaris disease, saprolegniasis, bacterial hemorrhagic septicemia, furunculosis, ulcer disease, gaffkemia in lobsters and various parasites. An investigational new animal drug exemption is a process by which the FDA authorizes and controls the use of unapproved drugs by qualified researchers to investigate safety and effectiveness.