Histopathology Alteration of Red Hybrid Tilapia (Oreochromis Spp.) Caused by Streptococcus Agalactiae Infection

Abstract

Streptococcus agalactiae is one of the streptococcal species most frequently associated with disease in aquaculture. The aim of this study was to assess the histopathology alteration and pathogenicity of S. agalactiae experimentally infected in red hybrid tilapia, Oreochromis spp. Streptococcus agalactiae was isolated from kidney of healthy Oreochromis spp. obtained from wet market. Then, 120 of healthy juveniles of red hybrid tilapia (50–70 g) were injected intraperitoneally with 0.2 ml of S. agalactiae suspension containing 104, 105, 106, 107 and 108 cfu/ml. Fish with clinical signs of streptococcosis were fixed in 10% buffered formalin and proceeded to histopathological examination. As a result, LD50 is 105.8 LD50/ml which is equivalent with bacterial concentration 6.1 × 106. The important histopathology findings were hydropic degeneration of hepatocyte, hypertrophy in liver cells, hemosiderin deposition and haemorrhages on spleen, dilated of Bowman spaces in glomeruli and nephrosis in tubule, and hyperplasia and fusion of secondary lamellae; all these finding were testament for Streptococcosis. In conclusion, this study showed that S. agalactiae isolate was able to produce clinical disease in Red hybrid tilapia, Oreochromis spp. experimentally.