Abstract

VASQUEZ-PINEROS, Mónica A.; RONDON-BARRAGAN, Iang S; RESTREPO-BETANCUR, Luis F  and  ESLAVA-MOCHA, Pedro R.. Clinical and hematological study of experimental infection with Aeromonas hydrophila and Edwardsiella tarda on tilapia Oreochromis sp. Orinoquia [online]. 2010, vol.14, n.1, pp.33-44. ISSN 0121-3709.

Opportunistic bacteria as A. hydrophila and E. tarda are related to haemorrhagic septicaemia outbreaks in cultured tilapias in our country, being the aetiological agents of highest participation on the diagnosis of infection disease in cultures of Oreochromis sp., in Departamento del Meta. This article reports a clinical and hematological study of tilapia hybrid (50-70g) during the experimental infection with Aeromonas hydrophila and Edwardsiella tarda made by intraperitoneal inoculation of 7 x 10⁸ CFU/ml and 2 x 10⁸ CFU/ml of A. hydrophila and E. tarda, respectively. From 11 hours infected fish showed paleness, lethargy, gasping, increased respiratory frequency and loss of swim axis. At hematological examination, infected animals showed severe lymphopenia, increased monocytes, hemolysis, increased blastic cells, karyorrhexis, hypochromia and anisocytosis, which is characteristic of a hypochromic anemia and erythroclasia described in fish bacterial infection. At necropsy examination, fish inoculated with bacteria showed: hemorrhages on the base of fins and internal organs, pale and mottled liver, increased abdominal fluid and blood-stained fluid in intestine, unlike control animals that did not show these lesions. Additionally, hepatomegaly was observed in experimental infected animals, even though there were not significance differences in the hepatosomatic index of these animals with respect to control. In treatment of E. tarda, whitish nodules with multifocal distribution were observed in spleen. During the present study, hybrid tilapias infected with E. tarda y A. hydrophila, showed a clinical condition compatible with haemorrhagic septicaemia, possibly associated to extracellular products (ECP), such as hemolysins and aerolisyns, with hemolytic and cytotoxic activity in fish, among other factors. This work is an approximation to a model of study of bacterial disease of tilapia with pathogenic strains isolated in the region.

Keywords : Bacteria; hematology; septicaemia; Oreochromis sp; tilapia hybrid.

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