Sourabh Kumar Dubey

Median lethal salinity (MLS96 h) of two small indigenous fish species Amblypharyngodon mola and Pethia ticto from Indian Sundarban.

Amblypharyngodon mola and Pethia ticto are small indigenous fish species belonging to family cyprinidae and considered as primary freshwater fish widely distributed in Indian subcontinent including Sundarban region. The 96-h median lethal salinity (MLS96 h) level of these fish was found out by exposing to saline water (0-10 ppt) in direct transfer method. The 96-h median lethal salinity for A. mola was found to be 6.20 ppt with 95% confidence intervals of 4.38-7.09 ppt where as for P. ticto it was 6.12 with 95% confidence intervals of 3.67-7.07 ppt. The Probit showed that at 6.12-6.20 ppt, 50% of the both test species shows sensitivity to salinity that leads to mortality. The regression analysis indicated that the mortality rate is positively correlated with salinity concentration having a regression coefficient close to 1.0 in each case. Various levels of external stress responses were noticed at 8 and 10 ppt salinity. The study suggests that these fish can potentially be used as a candidate species for aquaculture in slight brackishwater areas of Sundarban. However, further studies are required to understand the ecosystem based adaptation processes at higher salinity levels.

Assemblages of Total Mercury in the Tropical Macrotidal Bidyadhari Estuarine Stretches of Indian Sundarban Mangrove Eco-Region

The study was conducted to estimate total mercury in water and sediment of Bidyadhari river of Indian Sundarban delta in pre-monsoon, monsoon and post-monsoon period. Bidyadhari river presently serves as a sewage and excess rainwater outlet from the Kolkata metropolitan and adjacent area which ultimately empties at the Bay of Bengal in the course of the Indian Sundarban delta. Four different study sites situated around the course of the river were selected from the outfall of sewage canals at Kulti-Ghushighata (S1) where metropolitan sewages discharged and mixed up into water of Bidyadhari river which ultimately carried through this river via stations Malancha (S2), Kanmari (S3) to Dhamakhali (S4), just before the river confluences with the larger Raimangal river at northern Sundarban delta. Mean mercury concentration in collected water ranged BDL to 0.014 ± 0.001 μg ml-1 and sediment samples ranged BDL to 0.260 ± 0.014 μg g-1. Highest mercury accumulations in river water both high tide and low tide was found at S4 followed by S3 with pronounced seasonal variation. Mercury present in the sediment (0-5 cm) showed a remarkable site and season specific differences with highest concentration in S4. Box whisker plot revealed that one extreme value was found at the S4 along with one outlier was at S3 and five outliers were at S4 during monsoon period. Regarding total mercury assemblages, PCA analysis showed all the sites except S4 are significantly associated. Based on Effective Range Low (ERL) value it is considered that sediment is still low mercury enrichment with less ecotoxicological risk while level often above the requirement desirable limit of drinking water recommended by WHO.

Significance of Cross-contamination on Bacteriological Quality of Black Tiger Shrimp (Penaeus monodon Fabricius 1798) for Export Trade Produced in Fish Processing Plant

In this study, bacteriological quality of raw and processed Penaeus monodon produced for export trade from preprocessing, processing area and cross-contaminated sample was analysed in terms of total plate count (TPC), Vibrio cholerae, Escherichia coli, Staphylococcus aureus, Salmonella spp and Listeria monocytogenes from a HACCP (Hazard Analysis Critical Control Points) approved processing plant. In all cases bacterial loads were highest in crosscontaminated sample than the pre-processing and processing area. E. coli was present in cross-contaminated raw and processed sample; however V. cholerae, S. aureus, Salmonella spp and L. monocytogenes were not detected in any case. In pre-processing, processing and cross-contaminated samples, the TPC value was not exceeding the standard limits as per ICMSF (International Commission on Microbiological Specifications for Foods Standards) and EIC (Export Inspection Council) standard. Another side of the present work indicated that, microbial analysis of all the samples obtained from processing area were within the permissible limits. This study clearly indicated that maximum microbial load in cross-contaminated condition due to transfer of place, shifting of equipments, products etc. The present microbiological survey revealed that there is an urgent need for considerable improvement in the bacteriological quality of products and it should be free from cross-contamination. Strict observance to CGMPs (Current Good Manufacturing Practice) and HACCP plan can greatly improve the product quality and reduce the risk of cross-contamination.