Fishes play such major roles in human life, giving important sources of food and economic sustenance across the world. However, the high incidences of diseases in fish populations significantly pose a threat to aquatic ecosystems and food security. The high mortalities seen in marine fish caught for aquariums raise several important questions regarding water quality and ecosystem health. While fish illnesses do not always show a direct link to the water quality, they are indicators for such, which simply means better testing methods are needed. While a system where the examination is comprehensive would be desirable, cost and practicality due to the complexity of such examinations restrict such activities in many instances. It is important to address fish diseases, though, as a means to maintain biodiversity and ensure sustainable fishery practices for the future.