Report on high density population of a Cladoceran, Moina macrocopa and their gut microbes in anoxic sewage water: a potential bio-indicator of aquatic pollution

Zooplankton are essential components of the aquatic food chain. Their density and composition are influenced by abundant of particular nutrients which promotes planktonic bloom. Domestic sewage is mostly anoxic to hypoxia in nature that favours largely pollution resistant species of zooplankton. The present study deals with the density, biochemical composition and gut microbes of Cladoceran (Moina macrocopa) from domestic sewage water monthly and seasonally. Hydrological parameters and zooplankton density in sewage water showed much variation in different seasons. The monthly variations of M. macrocopa density showed minimum (766.67 ± 152 Ind./L) during December 2019 and maximum (11,600.00 ± 360 Ind./L) during March 2020. Further, seasonal mean density was minimum during monsoon (1444.44 ± 185 Ind./L) and maximum during post-monsoon (9744.44 ± 725 Ind./L) showed distinct seasonal variations. Untreated sewage water in canal boost up solitary zooplankton M. macrocopa abundantly even in anoxic condition with optimum nutrients during the post-monsoon season. Total proteins and carbohydrates of M. macrocopa were maximum during post-monsoon and minimum during monsoon whereas total lipids were maximum during pre-monsoon and minimum during monsoon season. Present finding reveal that, M. macrocopa was found in untreated domestic sewage waste water solitarily in high density in different seasons. Physico-chemical parameters and availability of rich nutrients were the key factors which favouring high density and biochemical profiles of M. macrocopa. Further, abundant anaerobic coli form bacterial strains viz. Klebsiella pneumonia, Exiguobacterium profundum, Escherichia coli JSG and Escherichia coli JSG2 in gut of M. macrocopa indicates its preferred food in anoxic condition and reflect well adaptation in polluted environment.