Evaluation of experimental infection with Aeromonas hydrophila in pacu (Piaractus mesopotamicus) (Holmberg, 1887)*

Silvia Patrícia Carraschi^1,2*, Claudinei da Cruz², Joaquim Gonçalves Machado Neto³, Flávio Ruas de Moraes⁴,  Oswaldo Durival Rossi Júnior⁵, Antonio Nader Neto² and

Neida Lucas Bortoluzzi⁴

¹Centro de Aquicultura (Aquaculture Center) at Unesp – Jaboticabal Campus – São Paulo – Brazil.

²Núcleo de Estudos e Pesquisas Ambientais em Matologia (NEPEAM) (Weed Science Environmental Research Studies Centre) of the College of Agricultural and Veterinary Sciences at Unesp - Jaboticabal – São Paulo – Brazil.

³Laboratório de Ecotoxicologia dos Agrotóxicos e Saúde Ocupacional (Laborseg) (Pesticides Ecotoxicology and Ocupational Health Lab) of the College of Agricultural and Veterinary Sciences at Unesp - Jaboticabal –

 São Paulo Brazil.

⁴Laboratório de Ictiopatologia (Fish Pathology Lab) of the College of Agricultural and Veterinary Sciences at Unesp - de Jaboticabal – São Paulo – Brazil.

⁵Departamento do Medicina Veterinária Preventiva (Preventive Veterinary Medicine Department) of the College of Agricultural and Veterinary Sciences at Unesp -  Jaboticabal – São Paulo – Brazil.

*Corresponding author. E-mail: pacarraschi@yahoo.com.br. Tel: (+5516) 3209-2630.

Accepted 21 October, 2011

 Abstract

The aim of this work is to determine the concentration of Aeromonas hydrophila to be inoculated in pacu (Piaractus mesopotamicus), so as to induce bacterial infection but not death during a period of at least ten days and, therefore, enable the development of treatment protocols. The tested concentrations were established through the Mac Farland scale and fish were subjected to three A. hydrophila infection concentrations (1.2 × 10⁷, 2.4 × 10⁷ and 1.5 × 10⁸ UFC.mL^-1) through intracoelomic, intramuscular and subcutaneous injections. The clinical exam was done 24 h after inoculation, and the clinical signs suggested aeromonosis in all three groups. In the lowest concentration, animals demonstrated few clinical signs of disease, and in the highest concentration, all animals died within 24 h of aeromonosis induction with acute infection. In the intermediate concentration (2.4 × 10⁷ UFC.mL^-1), all animals presented clinical signs of aeromonosis and kept living at the beginning of the time of treatment. Therefore, 2.4 × 10⁷ UFC mL^-1 concentration was defined as viable for the study of experimental infection in pacu by A. hydrophila, as the fishes were kept alive at the beginning of the time of treatment protocol with pharmochemicals.

Key words: Bacterial infection, fish, disease, antibiotics.