Common Diseases and Treatment

Publisher Summary This chapter describes several diseases, which can infect fish populations. The diseases described are selected on the basis of their prevalence or representative pathogens within their classification. Gill and skin diseases are often initially diagnosed by the observation of lesions visible to the naked eye. Unusual swimming or feeding behavior should be carefully recorded to provide clues as to the cause of the disease condition. Fish exhibiting lesions (ulcers, erosion, hemorrhaging) or abnormal behavior (such as gasping, lethargy, or dark coloration) should be selected and euthanized by an overdose of anesthetic. Yersinia ruckeri is a gram-negative, oxidase-negative bacterium that is a serious pathogen of trout, salmon, seabass, and fathead minnows. Infected fish exhibit dark coloration, red fins, eyes and mouth. The most efficient method of managing this disease is the use of preventive immersion vaccines. Viral diagnoses must be made using suitable fish cell lines at the appropriate temperature (host range) and pH. Tissue samples must be homogenized and centrifuged in media containing antibiotics and antimycotics or filter sterilized to remove particulate material and normal bacterial flora contaminants.