Bacterial microbiota of cases of necrosis of freshwater shrimp exoskeleton (Macrobrachium rosenbergii) in commercial rearing in the South Litoral of the State of São Paulo, Brazil has been studied. The lesions were presented as dark spots, black spots, varying sizes, in the superfie-cye of the exoskeleton and abdome, in the rostrum, in the urpods, in the pereipods and in the tweezers. In bacteriological culture, Aeromonas, Pseudomonas and Vibrio gêneros, which are commonly associated with this infirmity, have been isolated. These micro-organisms are present in the water and behave as opportunists. Taking advantage of previous lesions of the exoskeleton, they now use it as a substrate, causing necrosis in the affected areas and mutilation, or even death, depending on the extent and compromise of the body superfie-cye affected. In addition to these opportunistic agents, Staphylococcus sp. coagulase negative, Escherichia coli and Proteus sp were also isolated. These injuries were due to failures in food and health management and to the uncontrol of population density in the rearing ponds.