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"Marine bacteria were isolated from seawater, sediment, seaweeds, bivalves and submerged substrates collected from five sampling stations viz. Therespuram, Fishing harbour, Roche park, Thermal beach and Hare island, located along the coast of Tuticorin. Pigmented bacteria were selected for screening of antagonistic activity. Out of the 166 pigmented bacterial strains isolated, 62 showed antibacterial activity against the Gram-positive indicator organisms, Micrococcus, Lactobacillus and Arthrobacter which were isolated from the marine environment. Flavobacterium made uo of 67.74% of isolates followed by Alteromonas (29.03%), Pseudomonas / Alteromonas / Flavobacterium group (1.61%) and Micrococcus (1.61%). Seaweeds and bivalves harboured the highest number of bacteria, while sediment harboured the lowest number. The majority of the antagonistic marine bacteria were recovered from the samples collected from fishing harbour. Alteromonas was the dominant antagonistic marine bacteria. Antagonistic strains of Alteromonas exhibited a wide antibacterial spectrum against fish / shrimp bacterial pathogens viz. Aeromonas hydrophila, A. sobria, Vibrio alginolyticus, V. harveyi and V. fischeri. The crude extracts of the antibacterial substance, produced by Alteromonas strains, prepared using ethyl acetate, displayed inhibitory against Staphylococcus aureus, Bacillus cereus and A. sobria. These results suggested that the antagonistic marine Alteromonas strains could be used as probiotic and biocontrol agents in aquaculture systems to prevent / control bacterial diseases."