Abstract 

       Herbal plant extracts could be an alternative treatment for diseases. This research was carried out to evaluate the antimicrobial potential of several plant extracts against fish pathogenic bacteriaisolated from diseased or health Nile tilapia. This study selected twenty plant extractsto determine anti-bacterial activity by agar well diffusion method on trypticase soy agar (TSA). Aqueous ethanolic extracts of herbs were tested for activity against three fish pathogenic bacteria, including Aeromonas hydrophila, Streptococcus agalactiae and Edwardsiella ictaluri. Effective herbal plant extractswasselected to investigate the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values against representative bacterial stains by broth dilution method. The results shown that Terminalia chebula,Acacia catechu,Glycyrrhiza glabra, Psidium guajava, Houttuynia cordata, Piper sarmentosumand Garcinia mangostanaextractscould inhibit all strains of the test bacteria. However, inhibitory zone effects of A. catechuextracts showed the best activity against A. hydrophila, S. agalactiae and E. ictaluri of 22.66±0.29 mm, 24.33±0.09mmand 21.33±0.34 mmrespectively when compared with other herb extracts, with the zone of inhibition ranging from 8.33±0.84 to 19.33±0.04 mm. Generally, MIC and MBC concentration values of A. catechuextractsthat ranged between 6.5 and 12.5 mg/ml of aqueous plant extracts for all pathogens tested. The results suggest that herbal plant extracts showing several biological activities may be potent inhibitors as a naturalantibacterial in Nile Tilapia. This property might be useful for application on fish farming.

Keywords:Plant extracts, Antibacterial activity,Nile tilapia, Fish pathogens