Aquarium fishkeeping is considered to be one of the most well-liked pastimes worldwide. The ornamental fish industry currently boasts a trade of about 5.9 billion U.S. dollars. However, this sector is vulnerable to various disease problems due to pathogenic microorganisms and parasites. The outbreaks of infectious diseases of ornamental fishes are the major challenges for the aquarists as they are associated with high economic losses through reduced growth performance and increased mortality. In the case of ornamental fishes, infectious diseases could impair the performance of aquarium fish through colour change, scale loss, different pathological signs, morbidity and mortality. Bacterial, viral, fungal and parasites are common infectious pathogens of ornamental fishes. Tropical ornamental fishes are more susceptible to parasitic infections caused by various fish parasites, including protozoans, trematodes, cestodes, nematodes, acanthocephalans, crustaceans, etc. Many of the fungi are also considered opportunistic pathogens that affect several ornamental fishes. It mainly attacks the fish when stressed due to the unfavourable environmental conditions. These infectious diseases can be prevented and controlled by environmental management to minimize stress, maintaining water quality parameters, quarantine of new fish and live foods before introducing to the ornamental unit, regular monitoring of the behaviour of fish, etc.