Bacteria Associated with Biofilms in a Macrobrachium rosenbergii Hatchery

Biofilms are important biological structures formed on most submerged aquatic surfaces. They comprise a unique niche wherein a community of microorganisms co-exist. The study was undertaken to identify the bacterial flora associated with biofilms formed on the surface of larval rearing tanks in a prawn hatchery. Surface swabs of two randomly chosen larval rearing tanks in a hatchery were taken regularly throughout the hatchery cycle and the bacterial loads were estimated. The counts varied from 1.8x103 to 4.3x104 CFU.cm-2 in Tank I and 5.1x103 to 3.5x104 CFU.cm-2 in Tank II. No significant difference was observed between Tank I and Tank II in respect of biofilm bacterial count when enumerated (p<0.05). The common bacterial genera isolated in both tanks comprised gram-negative bacteria including Pseudomonas, Vibrio and Aeromonas. Bacillus and other non-spore formers were the predominant gram-positive bacteria isolated. Bacteria associated with biofilms are more resistant to antibiotics and water sanitizers generally used in tank water treatment. Biofilms can be a reservoir of pathogens and bacteria such as Pseudomonas, Aeromonas and Vibrio isolated from the biofilms in this study may be potential pathogens of prawn larvae in hatcheries.