Comparative Clinicopathological Changes Associated with Experimental Streptococcus agalactiae and Streptococcus iniae Cohabitation Infection in Red Hybrid Tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Streptococcus agalactiae and iniae are the two main pathogens causing streptococcosis in fish. This study compares clinicopathological changes red hybrid tilapia experimentally infected with S. or iniae. A total of 180 tilapias were divided into six groups. Groups 1A, 2A, 3A inoculated intraperitoneally sterile phosphate-buffered saline, agalactiae, Fish then immediately allowed to cohabitate fish 1B, 2B, 3B, respectively. All observed at 6-hr intervals for 120 hr before surviving euthanized. The spleen, liver, brain samples collected bacterial isolation histopathology. Clinical signs developed 72 2A 96 2B 3B. Group showed highest clinical score (P<0.05). Significantly (P<0.05), more cohabitating (Groups 2B) by compared (Group 3B) 55.0±0.0 43.70±1.25%, mortality rate was significantly (P<0.05) higher than other gross lesions common 2A. Histopathologically, encephalitis while meningoencephalitis 2B. findings suggest that is pathogenic iniae, producing slightly different histopathological brain.