Aeromonas hydrophila associated with mass mortality of adult goldfish Carassius auratus (Linnaeus 1758) in ornamental farms in India

Aeromonas hydrophila was identified the causative agent of a disease outbreak in goldfish, Carassius auratus from four ornamental fish farms in Kerala, India. Seven bacterial isolates viz., Plesiomonas shigelloides (NPPS-1), Aemmonas hydrophila (NPAH-1, 2, 3 and 4), Citrobacter freundii (NPCF-1) and Acinetobacter spp. (NPA-1) were isolated from the affected fish. Further, all four.4. hydrophila (NPAH-1, 2, 3 and 4) isolates were identified by amplification of gyrB and rpoD genes. The RAPD profile using 3 primers confirmed that all four A. hydrophila were genetically similar. No cytopathic effect was observed on goldfish fin (GFF) cell line after inoculation of the tissue homogenate from the affected fish and affected tissues were found negative for koi herpesvirus (KHV), cyprinid herpesvirus-2 (CyHV-2) and spring viraemia of carp virus (SVCV). Experimental challenge resulted in mortality of fish injected with A. hydrophila only. A. hydrophila was observed to be cytotoxic on GFF cell line and exhibited haemolytic activity on 5% sheep blood agar. A. hydrophila possessed multiple virulence genes viz., enterotoxins, haemolytic toxins and outer membrane protein as determined by PCR. A. hydrophila was sensitive to Cefixime, Chloramphenicol, Nitrofurantoin, Kanamycin, Ciprofloxacin, Furazolidone and Cefixime/Clavulanic acid. After treatment with the suggested antibiotics, the fish were recovered from the disease.