Fish diseases caused by viral, bacterial, fungal, and parasitic agents remain a primary constraint to global aquaculture productivity. This review synthesizes current knowledge on the etiological agents, pathological manifestations, epidemiological determinants, and evidence-based management strategies for major infectious fish diseases. The 'disease triangle' framework comprising host susceptibility, pathogen virulence, and environmental perturbation is employed to analyze disease dynamics. Environmental stressors, particularly temperature fluctuations, deteriorating water quality, and intensive stocking, are identified as critical predisposing factors that compromise host immunity and facilitate pathogen establishment. A systematic categorization of viral (VHS, IHN, SVC), bacterial (Columnaris, MAS, Edwardsiellosis, Furunculosis, BKD, EUS), fungal (Saprolegniasis, Branchiomycosis), and parasitic diseases (Myxosporidiosis, Dactylogyrosis, Argulosis) is presented along with their clinical profiles and recommended chemotherapeutic and prophylactic regimens. The review underscores the urgent need for integrated health management protocols and advances in immunoprophylaxis and environmentally sustainable biocontrol strategies.