Bacteria are ubiquitous in nature. Fish are constantly exposed to bacteria, and usually only succumb to an infection after having been exposed to prolonged periods of stress. Before making a diagnosis of a bacterial disease, it is necessary to eliminate the possibility of environmental or parasitic problems. Environmental factors may act as stressors and can predispose a fish to bacterial disease while affecting the fish simultaneously. Clinical signs caused by the various bacterial pathogens are very similar. Therefore, to make a definitive bacterial diagnosis, it is necessary to culture and identify the organisms involved.