摘要Objective: To investigate antibacterial effects of extracts from the seaweed Chondrococcushornemanni (C. hornemanni) on bacterial pathogens of marine ornamental fish. Method: Methanol extract obtained from C. hornemanni showed a broad and high antibacterial activity against four fish pathogens including Providencia rettgeri, Aeromonas hydrophila, Vibrioalginoticus and Vibrio parahaemolyticus. The crude extract obtained from the dried seaweeds was fractionated and purified using column chromatography. Purified extracts were analyzed with Fourier transform infrared spectroscopy (FTIR) for identifying the functional groups. Phytoconstituents of the active fraction were further identified by means of gas chromatography and mass spectrometric (GC-MS) analysis. Result: The first fraction of the extracts showed effective inhibitory activity against Aeromonashydrophila and Vibrio parahaemolyticus at a concentration of 100 μL. However, Vibrio alginolyticus and Providencia rettgeri had shown a moderately lesser inhibitory response to the extract.Conclusion:Hence, it is concluded that extracts of seaweed C. hornemanni, contain potential bioactive compounds with a considerable antibiotic activity.