ABSTRACT
Fish respond quickly to environmental changes which can affect their disease susceptibility and overall general health. A good fish health maintenance program must give careful attention to the interaction between a fish population and its environment. Epizootiology in a broad sense is the study of disease: the spread of pathogens, their mode of infection, and the control of disease in animals other than humans. When an obligate pathogen-caused fish disease outbreak occurs, predisposing factors that dictate the seriousness of the disease are: source of infection, mode of transmission, portal of entry, virulence of the pathogenic organism, and resistance of the host. Fish diseases are categorized according to severity of infection, rate of morbidity, and presence of clinical signs and are described as either acute, chronic, or latent. Mortality pattern is related to degree of infection and is helpful in determining whether cause of death is due to infectious agents, toxins, nutritional or adverse water quality.
