INVESTIGATIONS ON THE SUSCEPTIBILITY OF GIFT TILAPIA TO Streptococcus agalactiae INFECTION
Tilapia (Oreochromis niloticus) farming is one of the most important aquaculture industries and Streptoccocus agalactiae is a highly pathogenic bacterium of farmed tilapia. In this study GIFT tilapia were used to see their susceptibility to Streptoccocus agalactiae using three different concentrations of the bacteria, 6.2 x 108, 6.2 x 106, 6.2 x 104 cfu/ml. For each concentrations, eight healthy fish of 3-5 inch size of average weight 20-25 g were used. All groups were exposed to the different concentrations of S. agalactiae by intraperitoneal injection at the rate of 0.1 ml of the inoculum and observed for any signs of abnormalities due to the infection. Throughout the experiment, eye abnormalities, erratic swimming behavior, caudal fin damage, swollen abdomen and body lesions were observed in most of the experimental fish. Kidney, brain and eye samples were collected and screened for the bacteria and the histopathological lesions are also being investigated. From the experiment, GIFT tilapia was observed to be susceptible to S. agalactiae at concentrations of over 6.2 x106 CFU/ml causing death. The result showed that LD50 of the bacteria to GIFT tilapia was found to be 6.2 x 106 CFU /ml.
