Acute toxicity (LC50) of eucalyptus extract on the grass carp (Ctenopharyngodon idella) liver and gill tissues and its antibacterial effect against Aeromonas hydrophila

The purpose of this study was to determine the acute toxicity or 50% lethal concentration within 96 hours (LC50 96 h) of eucalyptus extract on the juvenile grass carp (Ctenopharyngodon idella) and the impact of the extraction on Aeromonas hydrophila. 180 grass carp with an average weight of 5g were distributed randomly in the five treatment groups with eucalyptus concentrations of 2000, 2300, 2600, 3000, 3500 ppm and one control group (with three replications). Lethal concentration of eucalyptus extract using logarithmic was found 2478.56ppm. Histopathological studies of gill and liver that were exposed to lethal concentrations of eucalyptus extracts, showed the lesions consisted of hyperemia and bleeding. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the antimicrobial agent were determined using tube dissolution method. The MIC and MBC of extract of eucalyptus against A. hydrophila were recorded as 0.25mg/mL and 0.5mg/mL, respectively. In conclusion, the extract of eucalyptus can inhibit the growth of A. hydrophila in a culture medium. Due to the adverse effects of antibiotics, they can be used as an alternative to controlling and destroying A. hydrophila.