Francisella orientalis in Aquacultured Tilapia (Oreochromis spp.): A Case Work-Up of Diagnostics and Pathologic Findings in the North Central Region (USA).

Tilapia (Oreochromis spp.) is an increasingly popular aquacultured fish worldwide. While tilapia enjoy a 'hardy-fish' reputation among fish farmers, they are susceptible to a variety of infectious diseases that can be difficult to recognize pondside and have similarities in their gross presentations. This report describes gross and microscopic dermal, renal, and splenic granulomas; isolation and identification of Francisella orientalis; intervention; and resolution of a F. orientalis outbreak in an aquaculture farm in the North Central United States where F. orientalis has not been reported previously. The outbreak resulted in peak daily mortality rates of approximately 2.7%. This case report highlights the current benefits of aquatic species-focused diagnostic testing for fish farmers at veterinary diagnostic labs and provides an anecdotal clinical example of a resolved francisellosis outbreak potentially influenced by increasing the water temperature.