Studies on Pathogenicity effect of Aeromonas hydrophila infection in juvenile red hybrid tilapia Oreochromis sp.

This study was conducted to evaluate the ability of motile Aeromonas species (MAS) to
induce clinical symptoms and some pathological changes in juvenile red hybrid tilapia. A standard
dose of infection was selected based on predetermined LD50. Infected fish were observed for any
clinical sign and symptom for 96 hours. Samples of liver, spleen and kidney were collected for
histopatological changes due to Aeromonas hydrophila infection. Clinical signs of fish included
abnormal swimming behaviour and loss of balance. Most of infected fish suffered from
haemorrhagic eyes and lesions on the body surface. Some of the them also developed bilateral
exophthalmia. Histopathological changes were observed in kidney, liver and spleen. The infected
liver showed severe congestion of hepatic veins and vacuoles formation while anterior kidney
manifested degeneration of excretory tubules and glomeruli followed by severe haemorrhages and
hyaline droplets degeneration. Spleen on the other hand showed tissues degeneration and vacuoles
formation. All targated tissues also showed deposition of haemosiderin pigments followed by
proliferation of melanomacrphage centres. Development of such symptoms was associated with the
infection with Aeromonas hydrophila. The current study has shown that MAS could serve as the
primary cause of severe infection not only in red hybrid tilapia but may also infected other
freshwater fish species.The results of histological analysis of various tissues indicates a direct
correlation between disease infection and histopathological disorders observed in the tissues.