The attempt of the present study is to achieve an approach of the magnitude of parasite induced secondary infection estimation of Vibrio, Salmonella and Pseudomonas loads as well as the total heterotrophic bacteria using a battery of biochemical tests. The parasitic isopod Nerocila phaiopleura was collected from commonly available fish Stolephorus commersonii at Parangipettai, India. Parasites settled on the branchial and external body surface of the fish causes red coloured skin lesions, where secondary bacterial infections were detected. THB and Vibrio counts were higher in the infected hosts than in the healthy fish and it was found to 7.2x105 and 3.5x103 cfu g-1 in branchial regions and 5.4x105 and 2.3x103 cfu g-1 in the body surfaces, respectively. Salmonella counts were found as 6.0x103 and 3.6x101 cfu g-1 in branchial regions of the infected and uninfected fish and in body regions, 3.9x103 and 1.03x102 cfu g-1, respectively. Pseudomonas counts were 7.0x102, 4.9x101 cfu g-1 in branchial regions and 6.2x102, 5.8x101 cfu g-1 in the body surfaces of the infected and uninfected fish. Statistical analysis of the results (t-test) showed high significant value (p<0.05).