Effective disease diagnosis and control measures can significantly reduce the losses caused by diseases in marine aquaculture and ensure its sustainable development. Common pathogenic diseases in marine fish mainly include bacterial diseases, viral diseases, and parasitic diseases. In this chapter, we mainly introduce ten prevalently marine fish diseases, including viral nervous necrosis, red sea bream iridoviral disease, photobacillosis with Photobacterium damselae subsp. Piscicida, nocardiosis, streptococcosis, vibriosis, cryptosporidiosis, fish lice disease, fish leech disease, and trypanosomiasis. For each disease, based on the introduction of the pathogen, the symptoms and pathological changes and the epidemiology were described. Additionally, detailed diagnostic methods and effective prevention and treatment methods are provided, aiming to help aquaculture practitioners enhance their disease prevention and control capabilities, ensuring stable and efficient production.