The Effectiveness of Halymenia durvillei Extract as Antibacterial Agent Against Fish Pathogenic Bacteria In Vitro

Abstract

The use of antibiotics in aquaculture has raised serious concerns regarding the emergence of bacterial resistance and adverse environmental impacts. Red seaweed (Halymenia durvillei) is known to contain bioactive secondary metabolites with potential antibacterial properties. This study aimed to evaluate the antibacterial efficacy of ethanol extract of H. durvillei against four fish pathogenic bacteria, namely Edwardsiella tarda, Aeromonas hydrophila, Aeromonas salmonicida, and Vibrio parahaemolyticus, using agar well diffusion and broth microdilution assays. The experiment was arranged in a completely randomized design consisting of five extract concentrations (100%, 75%, 50%, 25%, and 12.5%) with five replications. The results showed that E. tarda exhibited the largest inhibition zone (16.2 mm) at 100% extract concentration, followed by A. salmonicida (10.8 mm) and A. hydrophila (10.4 mm). In contrast, V. parahaemolyticus did not produce an inhibition zone in the agar diffusion assay. The broth microdilution test revealed minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 25% and 50%, respectively, for all tested bacteria. The red seaweed extract demonstrated both bacteriostatic and bactericidal activity, indicating its potential as a natural antibacterial alternative for disease control in aquaculture.