Determination of LC50 and Clinical Symptoms of

Aeromonas hydrophila is a bacterial pathogen in freshwater aquaculture causing the motile aeromonad septicemia (MAS) disease and inflict significant economic losses. This study aimed to determine the lethal concentration (LC50-48h) of A. hydrophila on Tor soro's fingerlings and investigated the clinical signs that appeared following the challenge test. Briefly, 150 fingerlings (3,4 ± 0,18 cm) were challenged by immersion means with 0 (control), 104, 105, 106 and 107 CFU/mL of live cells of A. hydrophila. Reed and Muench’s method’s determination of LC50-48h was calculated and all clinical signs that appeared during the test were recorded. The result showed that the LC50-48h by immersion was 1.0 x 106,66 CFU/mL with clinical signs observed as hemorrhages, depigmentation, lesions, anorexia, loss of balance, and enlargement of the abdominal cavity. Furthermore, based on the LC50-48h and the clinical symptoms, this study reveals that even though all symptoms are consistent among the fish, the severity of the disease tends to be prevalent and intense as the concentration of pathogen is higher