From the Greek ichthýs - fish, páthos - suffering, disease and lógos - word, teaching.

Ichthyopathology is the science that studies fish diseases, their causes, patterns and control measures.

A section of veterinary science that studies infectious, invasive, non-infectious diseases and poisoning of fish. Ichthyopathology is closely related to microbiology, helminthology, protozoology, pathophysiology, biochemistry, pathanatomy, hydrobiology, aquatic toxicology and other disciplines; it uses methods and provisions of these sciences in the study of epizootology, clinical course, pathogenesis, diagnosis, treatment and prevention of diseases and poisoning of fish and other hydrobionts. 

The specificity of ichthyopathology is due to the peculiarities of fish and other hydrobionts in the aquatic environment, where the conditions of occurrence and patterns of epizootic process differ significantly from the nature of the epizootic course among terrestrial animals. Many fish diseases are widespread and cause significant damage to the national economy due to death, sanitary rejection, reduction of condition of valuable commercial freshwater and marine fish and other hydrobionts. The causative agents of some human diseases are transmitted through fish (opisthorchiasis, diphyllobothriosis, gaff disease, etc.), so many ichthyopathological studies are aimed at protecting human health.