10.22376/ijpbs.2019.10.1.p1-12 Volume 3 Issue 2 2012 (April - June) Marine ornamental fishes are remarkably valuable due to their high demand in domestic and international markets. It is a growing global interest to maintain these fishes in captivity. The bacterial and fungal infection is the major drawbacks in captive condition. In the present study, in-vitro screening of organic solvent extracts (methanol and acetone) of green algae lessThan i greaterThan Halimeda micronesia lessThan /i greaterThan were tested against the aquatic pathogens lessThan i greaterThan Providencia rettgeri, Aeromonas hydrophila, Vibrio alginoticus, V. parahaemolyticus, Proteus proteus, Pseudomonas flurescens, Entrobacter lessThan /i greaterThan sp lessThan i greaterThan , Flavobacterium lessThan /i greaterThan sp lessThan i greaterThan , Edwarsiella tarda, lessThan /i greaterThan and lessThan i greaterThan micrococcus lessThan /i greaterThan sp. The antibacterial activity assay was tested using agar well diffusion method and the zone of inhibition was compared with the same produced by the antibiotic (Chloramphenicol) as a positive control. Crude extracts were analyzed with Fourier transform infrared spectroscopy (FT-IR) for identifying functional group of the crude extract. R.Ganeshamurthy , T.T.Ajith Kumar And N.B.Dhayanithi Seaweed, Halimeda micronesia, Fish pathogen, Antibacterial activity, FT-IR 213-220