Abstract: Nemipterids are one of the important commercial and demersal resources of Visakhapatnam coast. Most of the Nemipterus japonicus caught in this coastal area were found to have lesions over the body surface along with a typical mucosal polyp in the buccal cavity, showing clinical signs of exophthalmia, skin discoloration with deep ulcers, frayed fins, damaged gills, distended abdomen with calcified gonads and hemorrhages. Hence, the present study is aimed to know the aetiological agent causing these lesions and polyps. Therefore, the smears were collected in the form of swabs from these lesions. The smear was examined by Grams method and inoculated into selective media. The organisms isolated and identified by biochemical and microbiological studies. Out of 50 Nemipterus japonicus, subjected to the above microbiological studies, Klebsiella pneumoniae were isolated from 40 fishes, Vibrio species from 5 fishes and Enterococci species from the remaining. It is concluded that the disease in these fishes is mainly due to infection by Klebsiella pneumoniae.