Abstract
A Yersinia ruckeri infection was recorded in 2007 among a group of Nile tilapia, Oreochromis niloticus, from an earthen pond at a semi-intensive fish farm in Sharkiya Province, lower Egypt. The outbreak took place during the late winter-spring transition period, effecting a total of 130 out of 150 fish, with a prevalence of 66.6%. The affected fish presented typical signs of yersiniosis, including extensive lip, mouth, fin and skin hemorrhages and hemorrhagic gastroenteritis, together with congestion of the internal organs. Tentative confirmation of the Yersinia ruckeri isolates was achieved using polymerase chain reaction (PCR), conventional biochemical assays and the API 20 E system. Mortalities were the result of a sharp fluctuation in water temperature, predation due to migratory birds that 'stopover' at this site, and to overstocking of ponds.