Influence of nitrogen cycle bacteria on nitrogen mineralisation, water quality and productivity of freshwater fish pond: a review

Nitrogen is one of the prime influential macronutrients which directly stimulate the productivity of pond ecosystems. The steps involving chemical transformations of nitrogen bound in complex organic matters are dominated by a variety of nitrogen cycle bacteria responsible for mineralisation of organic nitrogen into inorganic forms. Application of excess nitrogen in the form of fertiliser may cause deterioration of water quality by accumulation of toxic nitrogenous compounds such as ammonia and nitrite. Over-stimulation of nitrogen beyond a pond’s assimilatory capacity may be detrimental to the aquatic organisms and needs special attention to keep water quality conducive for fish growth. Seasonal variations of physicochemical parameters of water and sediments directly influence the nitrogen cycle through population dynamics of nitrogen cycle bacteria. Potentials of surplus nitrogen deportation by denitrifiers create opportunities for management of nitrogen cycle in ponds. The magnitude of loss of ammonia is proportional to the abundance of the nitrifiers, which is positively correlated with phytoplankton productivity, thereby enhancing fish growth. Organic fish farming is the best way for enumeration of nitrogen cycle bacteria for sustaining the quality of aquatic ecosystems. The present review focused on nitrogen biogeochemistry of aquaculture ponds with issues on use of nitrifiers as bioaugmentors for management of aquatic resources and use of essential micronutrients to a certain limit to enhance the efficacy of nitrifiers for increasing productivity. Further investigations are required to establish region-specific cost-effective methods to monitor the nitrogen cycle, thereby intensify the abundance of nitrifiers for increasing aquaculture production in a sustainable manner.