Pathogenecity Test of Aeromonas Isolated from Motile Aeromonas Septicemia (MAS) Infected Nile Tilapia on Some Freshwater Fish

Background: Test of pahogenecity of fish pathogens usually done by injection or ingestion of the bacterial samples on the fish. Objective of the current research was to introduce a new method of testing pathogenecity of fish pathogens through an artificial infection system. The targeted method was to observe the pathogenecity in aquarium condition by direct infection of the system water with bacterial suspension. Methods: Pathogenic Aeromonas was isolated from naturally infected Nile Tilapia having symptoms similar to those reported for MAS. The Isolate was identified by microscopic observation and biochemical assay. Liquid culture of the pathogenic isolate was taken to observe its’ pathogenic effect on four freshwater fish, e.g., Labeo rohita, Cirrhinus cirrhosus, Oreochromis niloticus and Hypophthalmichthys molitrix in aquarium condition. Water was directly infected with bacterial liquid culture instead of injecting the fish intra-muscularly. Antibiotic susceptibility was determined by agar disc diffusion assay. Results: Aeromonas was non-harmful for L. rohita, C. cirrhosus and H. molitrix while it remarkably infected O. niloticus even in lab condition with a lethal rate of 66.7±11.7%. Aeromonas was found to be susceptible to ciprofloxacin and resistant to ceftazidime. Conclusion: The research study showed that pathogens could harm the fish hosts who are susceptible in aquarium condition.