Experimental vaccination against Aeromonas hydrophila in Colossoma macropomum: Bacterial characterization, lethal doses, and mortality

J. Coaguila-Dávila, C. Fernandez-Espinel, V. Flores-Dominick, L. Gonzalez-Callirgos, M. Medina-Morillo, J. Yunis-Aguinaga

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Aeromonas hydrophila is one of the most important pathogens affecting Amazonian fish. In recent years, outbreaks in native aquaculture species displaying hemorrhages, epithelial ulcers, and damaged fins, which often lead to fatalities, have been reported. In the current study, we characterized A. hydrophila isolated from an outbreak on a commercial farm of Colossoma macropomum (gamitana), one of the main native species farmed in Peru and South America. Gram-negative, motile, oxidase-, and catalase-positive bacteria were retrieved from diseased C. macropomum. Aeromonas hydrophila was confirmed by biochemical and molecular characterization. Virulence genes detection showed that A. hydrophila (FO129–26) harbors cytotoxic enterotoxin (act), hemolysin (hly), serine protease (ser), lipase (lip), flagellin (fla), and elastase (ahyB) virulence genes. Then, lethal dose tests (LD10, 50, 90, 99) were performed and stablished at 4.6 × 106; 6.4 × 106; 8.9 × 106; and 1.11 × 107 CFU mL−1 confirming the virulence of the bacterial isolate. Finally, there were used three methods of bacteria inactivation to vaccine gamitanas against this bacterium. 180 gamitanas (C: control; FO: formaldehyde-inactivated group; PH: peroxide-inactivated group; CF: chloroform-inactivated group) were challenged with the pathogen. FO and PH groups had better survival rates (∼ 40 %) than the control group. There were no significant differences (p ≥ 0.05) between the FO and PH groups. Fish from CF presented early mortality after vaccination, probably due to irritation caused by chloroform residues. Finally, this study shows the virulence characteristics of A. hydrophila FO129–26 in an important farmed native fish in Peru and broadens the geographic range of the presence of this pathogen worldwide. Vaccines are a good strategy to improve the resistance of C. macropomum against A. hydrophila. However, further research is necessary to expand our comprehension of the efficacy of this protective technique in Amazonian fish.

Original languageEnglish
Article number102118
JournalAquaculture Reports
StatePublished - Jun 2024


  • Amazonian fish
  • Gamitana
  • Pathogen
  • Virulence genes


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