Detection of sub-lethal concentration (LC50) of Aeromonas hydrophila Against Hybrid Lemon Fin Barb (Hypsibarbus wetmorei ♂ × Barbonymus gonionotus ♀) Early Fry

The common bacterial pathogens of cultured freshwater fish are mostly aeromonads, especially the pathogenic strains of Aeromonas hydrophyla. Early fry stages of fish reared in hatcheries face severe disease outbreaks caused by aeromonads. Disease challenge studies with pathogenic bacteria including Aeromonas sp. have become a more common tool used in the investigation of the effects of micronutrients and other immunomodulatory additives in fish diets. This study examined the sub-lethal concentration (LC₅₀) of A. hydrophila against hybrid lemon fin barb (Barbonymus gonionotus ♀ × Hypsibarbus wetmorei ♂) early fry for 14 days. Three hundred and seventy-five fry (24 days after hatching) averaging 1.8±0.24 mg were randomly distributed in fifteen 2L plastic tanks. Fish fry were submerged in varying concentrations of A. hydrophila (2.5×10⁵, 2.5×10⁶, 2.5×10⁷, 2.5×10⁸ and 1×10⁹ CFU ml^-1). During the trial period, early fry was fed with a formulated diet containing the optimum crude protein and lipid contents. The mortality of fry in each tank was recorded daily. The LC₅₀ of A. hydrophila for early fry of hybrid lemon fin barb by immersion was found at 6.06×10⁸ CFU ml^-1.