Bacterial diversity assessment of world's largest sewage-fed fish farms with special reference to water quality: a Ramsar site.

Bacterial community structure is one of the essential components of aquaculture dynamics and plays an important role in maintaining wetland health. The present work is an effort to study the structure of bacterial communities in the world's largest sewage-fed fish farms, the East Kolkata Wetlands (EKWs), along with their predicted functional metabolic pathways and correlation with environmental variables. Sequencing data analysis revealed the abundance of genera such as Arcobacter (0-50%), Pseudomonas (0-15%), Sulfurospirillum (0-9%), Cloacibacterium (0-6%), hgcI clade (7-29%), C39 (0-9%), V6 (3-36%), Fluiivicola (1-6%) and Cyanobium (3-8%) in the EKWs. Further, water quality analysis of three treatment groups, i.e. Sewage, Sewage F-1 and Sewage F-2, revealed that dissolved oxygen (DO), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) differed significantly and violated the standard prescribed norms (Central Pollution Control Board, CPCB, New Delhi) for fishery propagation and irrigation in India. Further, the correlation matrix analysis between the abundance of bacterial genera and environmental variables indicated that DO, BOD and COD were mainly responsible for bacterial community structure and their proliferation in the EKWs. Our results indicated that the abundance of genera such as Arcobacter, Pseudomonas, Sulfurospirillum and Cloacibacterium has an inverse relationship with BOD and COD. Our observations based on the bacterial community structure and deteriorated water quality indicate the ineffective functioning and poor management of this man-made constructed wetland.