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Sampling stages and time: The research was conducted during the period of October 2008 to March 2009 at a processing industry named Sea Resource Limited, Sadarghat, Chittagong. Experimental samples were collected from 5 stages of processing viz., receiving, after primary washing with 5 ppm chlorine, after final washing with 10 ppm chlorine, after blast freezing and after 1 month of frozen storage. Nine fishes were taken from each stage which were divided into 3 groups. Approximately 150g sample was taken randomly from each fish and ground in a previously sterilized grinder. After grinding, 50g sample from each group were taken for determination of total bacterial load, 25 g for Salmonella and 25g for Vibrio cholerae, Fecal coliform and total coliform according to standard laboratory procedure (US food and drug administration bacteriological analytical manual January 2001). Determination of total plate count for hilsa shad: Fifty grams of fish muscle was blended with 0.1% of 450ml peptone water in a sterile blender jar for 5 minutes. To make decimal dilution, 1ml mixture was transferred with the help of sterilized pipette to a test tube containing 9 ml of sterilized peptone water. In this way decimal dilutions of 10^-1, 10^-2, 10^-3, 10^-4, 10^-5were prepared. One ml of sample from 10^-3, 10^-4 and 10^-5 dilution were pipetted into previously prepared agar plates. After mixing and solidification the media, the petri-dishes were incubated at inverted position for 72 hours at 30ºC. After 72 hour of incubation, forming colonies were counted which had a range between 30 and 300. As there is sufficient evidence that 10^-1 and 10^-2 dilution contain more than 300 colonies, these two dilutions were ignored for determining total bacterial load. Determination of total coliform for hilsa shad: Nine test tubes of lauryl sulfate triptose broth (LSTB) with Durham’s tube ware taken to determine total coliform which were grouped into 3 divisions. Tubes were taken for first 3 dilution i.e. dilution no 10^-1, 10^-2, 10^-3., but not for 10^-4, and 10^-5 dilution. First 1 ml of sample was inoculated from 10^-1 dilution by sterile pipette to first test-tube of first group. Again 1 ml of sample was inoculated from 10^-1 dilution by sterile pipette to second test-tube, and lastly it was again repeated for 3 test-tubes of first group. By this way rest of the 6 test-tubes from 10^-2 and dilution10^-3 dilution were inoculated. All nine tubes were incubated at 37 ºC for 48 hours. After incubation, gas producing tubes were marked and recorded. After that, total coliforms were counted from the most probable number (MPN) chart from USFDA, Bacteriological analytical manual 6th edition 1984. Determination of fecal coliform for hilsa shad To determine fecal coliform, 2 test tubes for each gas forming LSTB were taken. Among those two test tubes one contained Brilliant green lactose bile broth (BGLBB) and another test tube contained peptone water/tripton water. Now to identify fecal coliform 1 loop (minimum 3 mm diameter) of sample from every gas forming test-tube was transferred to the test tube of BGLBB and the test-tube containing tripton water. Both two test-tubes were incubated in circulating water bath at 44.5±2 ºC for 48 hours. After incubation period, the gas producing tubes were identified and marked. Then tubes which produced gas on both BGLBB and peptone/tripton water was counted and the fecal coliform from most probable number (MPN) chart was identified. Determination of Salmonella for hilsa shad: At first 25g of raw sample was taken in a sterile bottle with 225ml of buffered peptone water and incubated at 37ºC for 48 hrs. After incubation 1ml of sample was transferred into 10ml of Salenite Cystene Broth (SCB) and 1 ml in Tetra Thionet broth (TTB). Both TTB and SCB bottle were incubated at 37 ºC for another 24 hrs. Then 3mm loopful incubated sample was streaked from SCB and TTB into the sterile petridish containing Xylen deoxycholate agar (XLDA) and Brilliant green agar (BGA). Both petridishes were incubated at 37ºC for another 48 hours. On XLDA petridish, Salmonella will appear pink or yellow colonies with or without black centers. On the other hand on BGA petridish typical Salmonella colonies appears as dark to deep black color. The colonies that were found positive by observing XLDA and BGA petridish were inoculated into Triple Sugar Iron (TSI) agar by streaking the slant and stabbing the butt without flaming the sterile loop. The colony was again touched by serial loop and inoculated into lysine Iron Agar (LIA) by stabbing the butt and streaking the slant. Then the TSI and LIA test-tubes were incubated at 37 ºC for 24 hrs. Salmonella cultures typically produce an alkaline (red) slant and acid (yellow) with or without production of hydrogen sulphides. In TSI and in LIA Salmonella culture typically produce an alkaline (purple) reaction in the butt tube. Only a distinct yellow coloration in the butt of the tube will be considered as an acidic (negative) reaction. All positive presumptive Salmonella culture of TSI and LIA were retained for biochemical characterization. For positive TSI culture, they were streaked on to Macconkey agar and nutrient agar incubated at 37ºC for 24 hrs. Determination of Vibrio cholerae for hilsa shad: At first 25g of sample were taken in a sterile bottle with 225ml of peptone water and incubated at 37ºC for 48 hours. After incubation they were streaked on thiosulphate citrate bile salt sucrose agar (TCBS), and incubated at 37ºc for 24 hrs. If suspected colony was found they were marked. Lightly touched to the center and picked with a sterile needle, and inoculated into TSI test tube and Kiglar iron Agar (KIA) test tube. After inoculating sample into TSI test tube they were incubated overnight at 37ºC. Vibrio cholerae will manifest in TSI as acid slant and acid butt (yellow) and will produce neither gas nor blacking in the butt i.e. hydrogen sulphid negative. In KIA as alkaline slant (red) and acid butt (yellow). To ensure the biochemical identity of Vibrio cholerae the following tests were performed according to standard laboratory procedures as described by US food and drug administration bacteriological analytical manual, January 2001.