Bacterial diseases are the main final causes (causa mortis) of mortality in tilapia culture, often acting as secondary or opportunistic agents with mixed infection by parasites. Some bacterial diseases have a seasonal pattern with increasing cases in some periods of the year, while others may occur throughout the whole cycle and are not necessarily related to climatic factors such as columnaris disease. The francisellosis, also known as visceral granulomatosis, and the streptococcosis, also known as infectious meningoencephalitis, are examples of seasonal diseases (Figure 3), primarily related to water temperature. Francisella noatunensis infection causes outbreaks particularly in periods with water temperature below 24°C (75.2'F), while the streptococcosis occur in outbreaks during the period in which the water temperature is above 26°C (78.8'F).
After infections have taken hold, use of antibiotic bath treatment has been reported effective for other species of fish. However, the FDA has not approved the use of antibiotic medication for treatment of myxobacteria infections in tilapia. Thus, treatment of tilapia cultured for human consumption is currently not a legal practice in the United States.