Fecal Strings Associated with Streptococcus agalactiae Infection in Nile Tilapia, Oreochromis niloticus

This study provides the first description of long fecal strings in Streptococcus agalactiae-infected fish. Nile tilapia (Oreochromis niloticus) were administered an intraperitoneal injection with 0.1 mL solution containing a 10-fold dilution from 101 to 106 cfu S. agalactiae/fish. While infected fish developed clinical signs commonly associated with S. agalactiae infection, up to 40% of infected fish in each group also produced considerably longer (up to 20 cm in length) fecal waste strings than unchallenged tilapia. Fecal strings from these infected fish were observed trailing from the anus and often became increasingly opaque and white over time. Though S. agalactiae was not isolated from the fecal strings themselves, all S. agalactiae-challenged fish sampled were culture-positive. Histologic examination of the intestines of infected fish exhibited the presence of sloughed intestinal mucous cells and enterocytes in the feces and the absence of normal fecal matter. The presence of long brown and/or white, opaque fecal strings may suggest a clinical sign of bacterial disease and the need for further clinical examination.